If you have any questions you want answered, feel free to drop me a note. If you’ve got a question, chances are, there are lots of others out there with the same question. So ask away!
Note: all comments are moderated unless I’ve approved one of your previous comments. Almost everybody gets thrown off by this, but I moderate comments to avoid spammers. The downside of this is that you won’t see your comments post until I’ve had a chance to review and approve them. Sometimes this can take days (sorry!) Thanks for your patience.
Ted's Energy Tips 
Help! We are in insulation limbo! Our brick veneer, wood frame house (1920s) has plaster walls in pretty good shape. Do we need to tear off the plaster to insulate the outer walls or can we somehow retrofit with closed cell foam or maybe blown in -moisture resistant rock wool? Climate wise, we are in NYC area. Thank you!!
These are very tricky homes to insulate without unintended consequences. The gap between the brick and wall is intended to be there to allow airflow which helps to carry moisture out. Filling in this space can have adverse effects if not done properly.
The space on the inside, between the plaster lath and wall is often very narrow – 1″ making it really difficult to do anything effective. Plus, the plaster seeps through the lath so if you try to blow in foam, it often encounters blocks in walls resulting in very poor cavity fill (i.e. a huge waste of money). With a wood frame wall, you might have enough space between the plaster and wall to insulate, but it’s still challenging.
Here’s a link to a very detailed article on this type of construction.
As you can see towards the end of the article, the successful retrofits involve what you note – tearing out the plaster walls and using a carefully designed structure of semi-permeable foam and internal walls. Personally, this solution only appears feasible if you’re planning a full “gut” of the property.
Another option, which is fairly extreme, but less so than a complete tear out, is to build in the interior walls and insulate those. What I mean is building a 2×4 framed wall inside your exterior walls and insulating those with spray foam between the studs (spraying right to your existing interior walls which are now outside of the new stud wall). you then sheetrock etc. and you have a new, insulated interior wall without messing with all the plaster or exterior brick. You lose a few inches and have to extend all the window jambs. Like I said, it’s fairly extreme, but more doable. The added advantage is that the new stud walls have space in them for running new (up to code) electrical wiring, switches, etc.
Sorry I don’t have an easier solution but there just isn’t one.
Thanks for your very fast reply! We have a 1 1/6″ air gap between sheathing and outer brick (which we don’t intend to touch!), and 3.60″ gap between sheathing and lath.
We have talked to an Air Krete specialist who seems to think it’s possible to insulate between sheathing and lath- but are still mulling taking out wall. Adding a wall is interesting idea (thanks!) but it’s not such a big house so we’ll have to consider our space too!
If you have any injected product like Air Krete, insist on thermal imaging of all affected walls before and after injection and get a written guarantee of full wall fill. I would recommend that you have an independent thermography specialist do the testing.
Cheers
And to clarify the comment these are non-load-bearing brick walls (house is a wood framed house with brick veneer) thanks!
Hi Ted,
We are trying to insulate the finished attic in our 1920’s house. This process is complicated by the presence of kneewalls on both sides. We have soffit vents under the eaves and two ridge vents at the peak of the roof directly across the roofline from one another. We have received conflicting information about the best way to insulate this space. One option is to fill the slopes completely along both sides and then blow insulation into the floor of the unfinished part of the attic. The other option is to fill the sloped sections from the unfinished attic floor to the top of the kneewall space and then insulate the vertical sides and the floor of the kneewall space. To us, the problem with both of these proposals is that the insulation in the sloped section will prevent air flow from the soffit vents to the ridge vents. Should we be concerned about ventilation in either/both of these options? If so, how can we best address this problem?
Thank you for your help!
I’m glad you’re asking these questions now rather than when your roof starts getting moldy and rots out!
Unless you’re going to use closed-cell spray foam sprayed directly to the underside of the roof decking, you’re likely to run into problems. I’ve seen terrible mold and rot problems when people put fiberglass batts or other fluffy insulation into the sloped section. This creates a “perfect storm” of conditions that virtually ensures problems. The insulation allows the roof decking to get cold (the purpose of the insulation). That’s fine. What isn’t fine is that the insulation of that sort, no matter how well installed, allows moisture through. When the warm moisture from the house goes through the insulation, it condenses on the cold roof deck.
When you spray foam directly to the underside of the roof deck, it’s virtually impervious to moisture. The problem there is that often there’s sections of the roof that is hard to spray, hidden by the interior ceiling or otherwise inaccessible.
Keep in mind that you want the insulation only between cold places (i.e. the outside) and warm places (your inside rooms). Typically, the logical (and easy) places to insulate are from the soffit, not blocking the vents, horizontally between the rafters along the floor of the attic knee wall space, which is the ceiling of the room below. Then straight up the back of the knee wall. The space between the rafters where it runs under the knee wall must be sealed air tight, usually with rigid foam board (the blue or pink stuff).
Here’s a website with diagrams that show this better than my words can describe.
If you have a door or hatch leading into the knee wall space, be sure that is well insulated and has a good gasket that seals it tight! The horrible little plywood hatches that most people put in are huge energy holes.
HELP! We built a new home and moved in August 2015. We have an open concept kitchen/living/dining. We keep smelling a wet dog odor but it’s only in the kitchen/living area. Pets are not allowed in our home so I’m assuming the odor is from our heating and cooling unit. The ductwork is all in the attic. I don’t know where to start to pinpoint the problem. This odor is driving me INSANE😩.
Kristie,
Odors can be among the toughest things to track down. You can’t see them and you have to rely on your nose to detect them.
What makes you think that the odor is from your heating system? I want to understand your thinking since you’ve been living with this for a while.
Describe the home so I can get a better mental image.
What’s underneath the area that has the odor? What’s above it?
Where in the room is the odor strongest?
Are the filters for the heating system clean?
Do you have a central humidification system associated with the heating system?
Are there any other sources of water or moisture in that area of the house? Large house plants. Fountains. Etc.
When did the odor start becoming apparent?
Answering these questions will help you pinpoint the problem.
Ted,
Thanks again for helping me with my crawlspace insulation logic. Now that I’m back to using rigid on the floor, do I want the vapor barrier above or below it? If I put the vapor barrier down first, then lay down the rigid, I’m worried that I could get condensation between the two if not perfectly air sealed. I also worry that if I put down the rigid, then vapor barrier over it, I may get moisture that migrates from the ground through the foam, but is trapped by the vapor barrier, and then can not as easily transfer back the other way through the foam. Or does it not really matter the orientation in this specific situation?
Thanks in advance,
-Andy
I’d go with the poly under the rigid. Typically the slab will be a high moisture environment anyway since it’s in direct contact with the ground. Concrete, when not subject to freeze-thaw cycles is moisture tolerant, so there’s little worry of damage or other problems. Unfortunately, most people don’t understand this and get nervous when they see water building up under the poly.
Then, the foam board above the poly also protects the vapor barrier. Invariably, people will go into the crawlspace and walk on the poly, store boxes, etc., creating lots of little holes and tears, reducing the vapor retarder’s effectiveness. So the foam will help to minimize these problems. Additionally, if you tape the seams, even if you get small holes in the poly and some moisture comes through, the foam will help provide slow migration of water vapor up and out.
OTOH, if you put the foam under the poly, I believe the foam would eventually become saturated with moisture and become ineffective as an insulator. And you’d also lose the protection of the poly by the foam. So, slab – poly – foam.
Hi Ted,
Love your site. I’m a 68-year old female who lives in Brooklyn, NY on the top two floors (3 and 4) of an attached (on both sides) brownstone building from the late 1800s. The oil burner is in the cellar. There is a crawl space adjacent to the cellar under a rear one-story extension. A year or so ago, we had the crawl space floor covered with concrete (the rest of the cellar has a sand floor); at the same time the old (hanging) insulation above the crawl space was removed. It was replaced with rigid foam insulation — but on the outside walls of the crawl space; unfortunately there are gaps in it. The downstairs neighbor says her apartment became too cold after that, so she started setting the building’s thermostat, which is in her apartment, higher.
The roof is flat with a bulkhead leading to a recreational roof deck. There are two mushroom vents and two large fans that protrude the roof itself. The roof was redone (just the top layers) about 16 years ago and is still apparently in good shape.
However, our apartment can be chilly, especially around the front windows and sometimes in the top floor hallway (under two skylights). I’ve weatherstripped the windows, doors, etc and that has helped a lot (and perhaps increasing the thermostat setting helped as well).
An energy guy (who mainly works on converting brownstones to passive homes) made some recommendations for comfort and energy savings that we are considering:
Blower test with air sealing.
2, Improving the insulation around the cellar crawl space (“intello densepack. Fix seal rigid along walls.(for thermal performance and air sealing”)),
2, Cellulose insulation blown into the attic including capping the high hats and removing the old messy fiberglass (with vaper barrier) batts.
Sealing the front windows from outside with new caulking and blowing cellulose insulation into them,
He made other recommendations as well, including replacing a metal roof bulkhead door with fiberglass (or insulating it) and caulking and insulating the back wall of the house similar to the front.
This morning I went up the to roof and saw that my roof (even where there is no recreational roof deck) was totally clear of snow while most of neighbors had a few inches left from our 2 + foot storm a week ago.
I want to make sure the fixes I do make sense. I am particularly concerned that the attic insulation recommendation does not include sealing anything besides the high hats. I’m also concerned about creating ventilation problems and about a failure to improve the existing energy issues.
Any thoughts you have would be most welcome!
WordPress.com / Gravatar.com credentials can be used.
Hi Judy, thanks for the clear description of your home and thoughts on the issues.
It sounds like your energy guy is on the right path. I almost always recommend the blower door test and associated air sealing as step one as it allows you to focus on the most important issues first. Hopefully, he has a thermal camera to use in conjunction with the blower test because the camera will show a lot of details that would be lost in just a general inspection. It takes the guesswork out of the inspection. If he doesn’t have a thermal camera, it’s worth looking around for someone who is experienced in their use. In your area, there should be many of those folks. One more word on this – usually people without the thermal cameras will claim that they don’t need one and give a variety of reasons why. That’s like a doctor telling you she doesn’t need an x-ray machine because they can look and see your broken bones. Don’t buy it!
Anyway, assuming that they do the test, they’ll know exactly where the cold air is coming in/warm air is escaping. Given you excellent observation about the roof snow, you clearly have some serious heat leaks to your attic space.
The other recommendations appear sound. Once the inspection is done, the report should prioritize the issues so you can focus on the big issues first and work your way through. In medicine, it’s triage. Fix the things that’ll kill you first then move on to less critical areas.
Feel free to ask more once you’ve talked with the energy people more.
Thanks, Ted! Appreciate the knowledgeable advice!
Hi Ted,
I ran across your site while researching information on HVAC condenser/blower operations. I am hoping you can provide guidance regarding my HVAC operating parameters. First, I live in SE AL where the normal winter temp is between 45-65F and the normal summer temp is between 90-100F. This winter, temperatures have been a bit colder and I am not confident my system is operating as it should. Second, I have an American Standard 4T two stage/variable speed outdoor unit, an American Standard 3/4 variable speed air handler, and an American Standard acculink comfort control thermostadt. My concern is the length of time the outdoor unit runs before shutting off. Here are the operating conditions: outdoor temp 33F; overnight indoor set temp: 65F; morning indoor set temp: 73F. System turns on at 0445 and indoor temp of 73F is reached by 0515. The outdoor unit runs for 5-6 hours after the indoor set temp is reached before shutting off. Cycles off for about 3 minutes and then turns on again and continues to run. I had it serviced and refrigerant was added. Here is how the system now operates-operating conditions yesterday: outdoor temp 53F; overnight indoor set temp: 65F; morning indoor set temp: 73F. System turns on at 0445 and indoor temp reached at 0454. System then cycles on and off as indicated: off @ 0522, on @0526; off @ 0542, on @0544; off @0555, on @0559; off @0610, on @0614; off @0625, on @0629. I stopped monitoring it and then started again later in the day because the system was cycling on and off six times in one hour (outside temp is 54F; indoor temp set @73F): on @3:10pm, off @3:14; on @3:20, off @3:25; on @3:31, off @3:35; on @3:41, off @3:45; on @3:51, off @3:55. Continued to operate this way until sleep mode at 10:00 pm. This morning I again monitored the system and here is what it is doing: outdoor temp is 45F; overnight indoor set temp: 65f; morning indoor set temp: 73f. System turned on at 0445 and indoor temp of 73F was reached @0454. System turned off @ 0455 and on again @0500. It is now 0810 and the system has yet to turn off. The blower has cycled through 1st and 2d stage but neither the outdoor unit or the blower have turned off. THIS CAN’T BE NORMAL OPERATING PARAMETERs, right? The service tech was out for 6 hours two days ago and checked everything including duct work, number of vents per room/house sf, ect. Plus, the thermostat was replaced a week ago. Nothing seems to be working.
There seem to be a couple things going on here.
First, the system brings the house up to temperature from 65F to 73F in a short amount of time by cranking out with maximum backup heat (assuming that you’re talking about a heat pump with electric heat strips). When you use a large temperature setback at night, the thermostat will usually force the backup heat to come on. The backup strips cost 3-4x as much to run as the heat pump by itself. A properly set up, modern heat pump will have an outdoor temperature sensor that will try to minimize the use of the backup strips if the temperature outside is about a certain temperature. In your climate, the backup strips should almost never need to come on since the heat pump itself can satisfy the heating requirements. That’s just the basic startup and really shouldn’t matter too much to your question but I add the information to provide some background for people interested in the way things work.
Next, the short-cycling of the system.
Given the times you listed (thanks for that extremely useful information!) – your system is either oversized for your heating requirements or improperly configured. Having a system that cycles on and off for only a few minutes at a time is hard on the equipment. It’s considered better if it comes on and runs for a longer period then turns off for longer, etc. The American Standard thermostats have a configuration setting called “cycles per hour” (Option 5 – see this link for the manual) They say ‘9’ is the recommended value for electric heat pumps which is a lot but if that’s what they recommend, then it seems like your system’s behavior is normal.
Question for you – does it feel like the house gets cold fast? If so, you may have other problems with insulation and air sealing. That would force the system to come back on too quickly. But what you’re experiencing seems extreme. You’d practically have to leave the door open in winter to cause the temperature to drop that quickly at the mild temperatures you have. But given the manual and settings, lots of cycling seems normal enough. Perhaps it’s just because they’re using the first stage and trying to maintain a steady temperature.
You may also want to look at the thermostat’s option 2 for temperature control in heating. They have “more aggressive” or “less aggressive” temperature control. I’d personally set it to “1” for the least aggressive temperature control to get the best efficiency. It’s like using the accelerator in your car. Slam it to the floor if you want to get up to speed fast but waste gas vs. slowly accelerating to speed for most efficiency.
As far as what I think you main question is – the long run time of the outdoor unit. That does sound abnormal. Normally, the compressor would be cycling on and off along with the thermostat. It might run a bit longer to protect it from short-cycling, but staying on continuously for five hours seems odd. However, I can imagine why it might do that. Consider this.
Suppose the compressor stays on for five minutes after the end of a heating cycle so as to protect the compressor from cycling on and off too much. Now, if the thermostat clicks on after only 4 minutes (like in some of your sample times) then the compressor would not turn off between cycles and would stay on continuously as long as you have a call for heat every four minutes or less. That could create exactly the condition you’re describing.
Reducing the heating aggressiveness could fix this problem. With less aggressive heating, the heat cycle would last longer and would take longer between cycles allowing the compressor to turn off normally. Note that the 5 minute number I quote above is a random number I used for example – I don’t know what value American Standard uses. But the theory is the same. Fewer cycles will allow the compressor more time to “rest” between cycles and will be more likely to turn off.
So have your technician check the setup parameters for the heat pump and switch it to the least aggressive heating mode. You should also have backup heat come on at the lowest possible temperature if you have an outdoor temperature sensor. This will make the system operate most efficiently and result in slower temperature swings which should, overall, be more comfortable. The downside is that it will take longer to come to temperature when you have a big temperature difference between the thermostat set point and the current indoor temperature. Same as the car analogy.
Hope that helps.
Hi Ted, thanks for the quick response. I should mention that the thermostat is never “clicking on” and that the indoor temperate gauges (actual temp and set temp) remain constant at 73F even though the outside unit and blower are cycling on and off every few minutes.
To answer your question, no it does not feel like the house gets cold fast; I have a relatively well built house with relatively good window and frame insulation.
I have the acculink comfort control manual in front of me and there are actually five separate CPH categories: 1) 1st stage compressor CPH; 2) 2d stage compressor CPH; 3) 1st stage heater CPH; 4) 2d stage heater CPH; 5) 3d stage heater CPH, so I am not sure which ones the technician should adjust.
Here is what the manual recommends: 1) 1st stage compressor CPH (2-6 avail; 3 recommended; 2) 2d stage compressor CPH (2-6 avail; 3 recommended; 3) 1st stage heater CPH (2-6 avail; 3 recommended; 4) 2d stage heater CPH(2-6 avail; 5 recommended; 5) 3d stage heater CPH (2-6 avail; 5 recommended). what do you recommend?
I can’t find anything in the manual that indicates temperature control in heating (more or less aggressive). Could this be called something else so I can find it in the manual?
thanks, Kim
Just saw this.
Ok, so it’s just cycling quickly to maintain a very stable temperature. My other reply had the specific pages of the manual with the settings including the heating aggressiveness one.
Given that your house temperature is staying very stable, you could probably reduce the CPH. I’m not familiar with your specific unit but you can see what the current values are for those settings and reduce them to a lower number of cycles without hurting anything. But I’d try the aggressiveness first.
Good luck!
Sorry, here is the link for the manual for my thermostat, which is the 900 series not the 802 you were using. http://www.denverwinair.com/literature/american_standard/thermostat/acont900-install_guide.pdf
I am going running; way too stressed.
No problem. That thermostat has the same settings. Just mention to your HVAC person to check those settings to try the least aggressive heating mode (page 14, table 4).
In addition to that, you could have them change the other setting for cycles per hour to see if that helps the problem of the compressor running constantly (page 9, table 4). You could set them to the ‘E’ setting which is supposed to automatically set it. If it’s already set, then you could try a manual override of ‘3’ or whatever.
If your system still misbehaves, you’re going to have to contact the factory rep, not your HVAC installer, who may be in over their head if they haven’t been able to figure it out.
Ted
Great format and information. I searched around and wasn’t able to find my topic so if this question has been asked before I apologize in advance for duplication.
I have a new Studio space above new garage. The Studio space is 784 sq’ (+/-) with a vaulted ceiling about 10′ high. I need to maintain RH to 50% or lower in this space. I am installing a ductless Heat pump system. From my research looks like I may have a serious problem maintaining that RH given the lack of humidification at lower temps. I live in the Pacific NW. The weather is fairly constant 50 and raining. I experience High RH given I am right at the shore of the Puget Sound. Any advice for maintaining RH 50% with ductless given the cooler outside temps with high outside RH ?
Thanks Ray,
I should create an index of topics. Thanks for persevering and posting the question.
Honestly, in your situation, you may be best off with a really good dehumidifier to use in conjunction with a mini-split. There are some really good units that are pretty energy efficient and intended for high use. They cheap units are very inefficient and tend to die if used continuously.
For example, something like this
http://www.sylvane.com/santa-fe-compact-dehumidifier.html
You’d want to Google a bit more for one that’s perhaps a little smaller/cost effective, but that one is a known quantity.
Hope that points you in the right direction.
After taking a closer look the Gap is in one location only. it’s located by the attic stairs and for ventilation with the gable windows the rest of the roof look sealed. so with that said should i put down a vapor barrier and insulate above the floorboards leaving the space between ceiling of 2nd floor and the floor boards or should i insulate on top of the plaster and lathe?
again thank you for your advice.
Matt,
If you’re going to put down a vapor barrier, you should go right on top of the plaster and lathe ceiling. In most climates (that aren’t extremely cold), typical practice is to skip the vapor retarder and just go with insulation. Pulling up the floorboards is a pain but it’s worth it because even that little gap can really diminish the effectiveness of the insulation. To the sweater analogy – imagine if you had an inch gap between your body and the sweater – you’d freeze! So insulate away.
Ideally, if you pull up the floorboards, you would best off having closed-cell foam (this is the really hard foam) sprayed right to the top of the plaster/lathe. This allows a good level of R-value and maintains the usability of the attic for storage etc. Loose fill or batts typically renders the attic useless for storage if you want a good level of R-value.
my “new to me” house is 140 years old and has no insulation in the attic, the house is plaster and Lathe with Oak beams. the attic has 1″ floorboards that I can pull up if needed. the issue I’m having is there is a small gap between the roof and the walls in the attic under the floorboards. (I can see the daylight) so if I just insulated the attic floor I’d get little benefit due to this gap between living space and insulation. the attic has gable venting too 2 windows one side and one on the other. What would you suggest?
That vintage can be truly challenging to make more energy efficient without creating “unintended consequences.”
I’m having trouble visualizing what you’re describing. “there is a small gap between the roof and the walls in the attic under the floorboards”
As a general rule, you do want the insulation right up against the surface shared with the inside of the house. They like to say “it should fit like a sweater.”
Could you describe your situation a bit more and I’ll do my best to answer.
Ted,
You’re totally right! That’s why I check with you. I didn’t even think about the vapor barrier being on the wrong side. I think my best bet is to stick with the rigid so I can spray foam & glue all the seams and help to eliminate any moisture from getting under the foam and condensing on the plastic. I’ll pump a little bit of conditioned air in there to pressure the space and take the edge off the temperature and I think I’ll be good. It is just a crawlspace after all.
sounds good. glad to be able to logic through this with you.
Ted,
If my crawlspace is air-sealed from moisture, would it be safe to put fiberglass on the floor instead of Roxul? Obviously Roxul is only 3.5″. If I used fiberglass I could use something like an R30 or R38 to really increase my insulation, or am I flirting with disaster?
I feel like there is a really good reason not to do that, having seen so many rotten batts that have fallen out from between the joists. I know rodents love nesting in insulation.
Here’s something – if you insulate, then the vapor barrier is on the “wrong” side so condensation would tend to form on the plastic under the insulation even if you sealed it well since there could be enough ambient moisture in the crawl space itself.
Bother! WordPress ate my last post, I think! So here goes again.
I have a brand new house and your advice here has been invaluable, Thank you.
I have an unused basement with three Gree mini splits rated at 16 SEER each. Then my main level has a standard split system rated at 12 SEER.
Is the difference in efficiency enough for me to ponder turning up the heat on the basement mini-splits to help supplement the upstairs unit? Or should I leave those units off unless I’m using the basement?
In short, is there a way to calculate the most efficient balance between the mini-splits downstairs and standard unit upstairs? Or is the difference in SEER rating not enough to matter?
Thanks Jim.
I have a similar inner debate with my systems and have come to the conclusion that I shouldn’t run the downstairs systems hoping that they’ll reduce the heating upstairs enough to warrant it. Here’s why:
Heat loss is proportional to the temperature difference between the inside and outside. So if you turn up the downstairs systems and the basement isn’t perfectly insulated, then you’ll lose more heat to the ground /walls /floors. It is likely that the amount of heat loss exceeds the increased efficiency of those systems so it’s a net loss of efficiency to run them more and the upstairs system less.
In my own home, I do sometimes run the downstairs systems warmer than I might otherwise just to keep the floors warmer, but that a comfort issue. Normally, I turn the heat off or way down in the basement.
Good thoughts. Yes, I think it’s 75% loss through the roof (or ceilings) and 25% through the walls so, yeah, the difference in SEER ratings could not make up for that. That seems obvious now. Thanks for pointing that out.
We have heat pump we live in mo. When the temp get below 32, it will run and won’t turn off, at time will still run after it is turned off! Sometimes it does cold air and will drop the temp in the house, we have different hvac people work on it, it still does it the last guy said to run a humidifier, and see if that helps, it doesn’t matter if we run it on emergency, it still does the same thing
Heat pumps can be confusing and temperamental beasts! When it gets cold out, the coils will freeze up. This is normal. So, what they have to do is run in air conditioning mode periodically, which makes it colder in the house but melts the ice off the coils outside. They’re supposed to minimize the amount of air flow in the house so as to reduce the amount of chilling. This is called the “defrost cycle.”
If the system is running properly, there should be heating coils in the air handler, or you should have another backup heating system, but I’m guessing yours should have electric backup heat. It sounds like your backup heat isn’t functioning properly because that’s supposed to run when you put it on emergency.
Here’s an easy test – switch to emergency heat and let the system run for maybe 20 minutes. The heat should come out noticeably warmer after a bit. If it doesn’t, then your HVAC company should check out the electric backup heat strips. There’s a chance that the big switch (called a “contactor”) is malfunctioning. This would prevent the electric heat strips from coming on. There should also be a big circuit breaker, maybe 40 to 60 Amps, that might be flipped either on the side of the air handler or in your main circuit box (or at both locations). Make sure those are switched on. Your HVAC company should have checked all these things first off but it may also be that they’re simply not very good with heat pumps and you should look for a different company! Anybody familiar with heat pumps should have told you at least these few things.
If you still can’t figure it out, feel free to drop another note. We’ve got some really sharp readers who might have other ideas for you.
We get popping and cracking in our ceiling or upper wall during sunrise and sunset. Our house is brick and the sound comes near where a fireplace is located. The ceiling is a cathedral ceiling. In the attic, the are before the roof slopes is filled with 18 inches of blown in insulation. The cathedral ceiling has rolled insulation. I noticed at the end of the ceiling the air deflectors are laying on top of the insulation and it appears the insulation is humped up partially blocking the airflow. The truss system is laid 24 inches apart and there is no air vent above the section where we hear the noise (between the wall and the 2nd trust). The decking is plywood and they used clips when it was installed. Do you think I need to add more vents or do you have other suggestions.
Sorry, just saw your question.
The popping and cracking sounds are typically associated with different rates of expansion/contraction of the building elements as the house warms/cools, particularly at sunrise and sunset. Imagine the roof heating up at sunrise. It quickly warms and expands. But there’s some resistance so it’s not a smooth process. Then, at some point, the forces are great enough and “POP” it lets go and moves. Just like the way an earthquake happens.
If it’s happening around the chimney, it might be that the builder or someone tried to firmly attach the roof to the chimney (which expands and contracts slowly with temperature changes). So you can imagine the roofing material trying to move and the fireplace trying to hold it in place. Just a guess, but worth looking into.
If you can, I’d inspect the chimney and the roof around the chimney from both the inside and outside of the house. Probably best done by a professional. I’d want them to make sure the flashing and connection between the two are done properly. It could also be interior, such as where the cathedral ceiling meets the chimney. Same thing could happen. You’d be looking for any signs of cracking or other things indicating a stress point. That will help you determine the seriousness of the issue. It might be just scary and nothing to worry about or it could be something worse. But definitely worth knowing what’s going on.
Thanks for your reply. I was able to isolate where the “pop” occurs which is the roof area by a vent that covers a rafter. The noise you hear downstairs from the pop sounds like it’s from the ceiling or wall 5 feet from a fireplace flu and 10 feet down from where it actually is popping. I’m guessing the pressure is pushing decking closer to area near the fireplace flu. When you hear the noise it sounds like it coming from the ceiling or possibly the wall. There are no cracks in the ceiling or walls. I’m thinking that it might be best to remove that vent and cover the opening and add more vents to balance the air flow. Do you think the vent opening over the rafter is causing the problem?
These issues are really tough. You may be on to something with the vent. Perhaps the air flow, which you generally want, is aiding a rapid heating and cooling of that area.
Before doing anything permanent, I would try possibly blocking the vent in that area just to reduce the air flow and see if that makes any difference. That way if it doesn’t, then you haven’t change the house in a way that could be negative.
That’s a great idea. I’ll let you know what happens. I noticed the airflow at the end of the rafter is mostly blocked by the insulation.
Hi Ted,
I am struggling with understanding the best way to insulate our “new-to-us house” in Northern California (Marin County). We have from bottom to top (or inside to out): a tongue and groove vaulted ceiling, feltex, a batten system that consists of “vertical 1×4’s and horizontal 2×2’s, nailed into the frame work of the house (apparently this creates a 2 ¼ inch above deck air space) and then steel rock coated panels (Steel Rock Roof Product) attached to the batten system. The tongue and groove is gapping in parts and where the “rib” beams exit the walls I can see daylight shining though (the original owner had caulked these exits years ago but it has shriveled away). The roof is fairly new (no insulation other than the “air space”) so we have to insulate from the inside. We were considering rigid or blown (open or closed?) insulation above sheet rock. The sheet rock would sit below the beams (so completely hiding all the beams and T&G). We also need lighting and had thought of recessed LED cans. Below is a link to a photo of the ceiling (before the wall to the kitchen and dining room came out, it looks like that through the entire upstairs) and a link to the roof specs. Thank you for any advice!!
http://www.steelroofingsystems.com/srs/specs-on-steel-roofing-systems
Thanks for the detailed explanation, photo, and spec sheet – that really helps me to better understand your construction.
Your climate there is wonderful, so at least you won’t be battling frigid winter weather and hot summers. In spite of that, I’m surprised that they still build with no insulation.
Those exposed beams, while beautiful, can be a construction and energy efficiency nightmare. My folks home has those and the first thing I did was fill the gaps with foam and sealed it up to stop the drafts. The low expansion foam used for tight spots like around windows and doors works quite well in this type of space and remains stable over time except where exposed to direct sunlight which destroys it. But at the inside junction of the beam and wall, it should work fine.
The easiest and most cost effective solution to insulating the ceiling would most likely be rigid foam board, installed between nailers which would be used to support the internal sheetrock. With poly-isocyanurate foam board, you get about R-5.6 per inch. Browsing through building requirements in your area indicates that they want R-30 or greater to be Title 24 compliant. I’m not sure if that applies to you, but best to double check everything with your local building officials.
Using that as a reference figure, you’d need 6″ of poly-iso foam board. With multiple layers of foam, installed with staggered seams, that would form a very tight air seal. And using one of the low-profile LED pseudo-recessed light fixtures, you’d have no problem with compromising the insulation.
Sounds like a very doable project that should have some good, tangible benefits for your comfort and energy efficiency.
I ran across the Marin County Energy Upgrade California program which looks like you might be able to get some of these renovations funded if you have a certified contractor do the work.
Ted,
Thank you so much for your response and the link to the upgrade program. It seems you prefer the rigid foam board, is that because of cost or is there another reason to stay away from the blown open or close cell insulation?
for a ceiling like that, a flat surface would be nice because you could layer the sheet rock right over it. The spray foam is lumpy but it really doesn’t matter in the long run. Foam has an easier installation so that is a plus. Closed cell is my preference due to much higher R-value per inch.
The ‘Ask Ted’ page doesn’t have a space to ask a question. So, I’ll ask it here and hope it gets the the right place.
I’ve tried to read through the huge amount of information you have on your amazing site, but I’m under the gun timewise to get Specification of Repairs in to the lender on an FHA 203K loan. I’m still fighting to get details from the contractor on re-roofing the first floor of the house I’m buying. The house has an existing gable metal roof, but will be replaced with shingles. The contractor, so far, has only specified: GAF asphalt shingles over CDX plywood with peel & stick waterproof membrane on plywood joints, and #30 felt, with an aluminum drip edge and a ridge vent. But reading some of your articles, I don’t know if that should be done without adding soffit vents?
I’ve asked him to estimate adding insulation to the first floor attic space while the roof is off. The house is in Florida. I have no idea what to accept or request in his proposal.
I wish I could send a picture of the house, because I can’t even tell where insulation can/should go on the first floor. It’s a 1945 one-story with a one-room 2nd story addition in the center with an open (steep) stairway from the first floor and a hatch from that upper room into the upper attic. The upper attic houses the A/C handler and has what looks to me like a spaghetti arrangement of flexible ducting and has blown insulation on the floor. I can see that part, but have no idea where space will be for insulation on the first level, so I wish I could send you a photo.
Any suggestions you have that I can ask the contractor to estimate will be greatly appreciated. Unfortunately, the lender is asking that we have the specification of repairs to them by this week. We’re already almost 2 weeks late already. I’m so afraid this is going to end up a botched job!
Thanks so much for your wonderful, informative site. I just wish I had discovered it before tonight at the 11th hour!
It’s always tough when time is limited. I would definitely recommend multiple quotes on the job. As you pointed out, you do want to ensure that matching soffit vents are installed with the ridge vent or the air flow will be minimal.
The insulation contractor should be able to tell you where insulation should go above the first level. If they can’t, find another company. Sorry that I can’t advise you more specifically but really you need someone there you can trust to advise you on the details.
Concerning SPF application on walls, is there any consensus on guidelines or good articles or advice on deciding on ccSPF vs. ocSPF? (seen articles pointing both ways without a satisfying answer)
I was considering doing closed cell on a wood frame extension with vinyl siding over wood (looks like panelboards), but was wondering if open cell might be smarter/less risky, and how to check to be sure ccSPF would not create a double vapor barrier first. In my wall’s case there appears to be no insulation at all, or inconsistently installed fiberglass, which would be removed first. I was leaning towards going ccSPF for a one job application (same truck as the roof deck) with fewer inches, but then was concerned if blocking moisture would be bad for the wood for some reason I haven’t considered.
I’d go closed-cell all around, unless I’m missing something special about your construction. Where are you concerned about the double vapor barrier?
To remind others, open cell foam is much more vapor permeable and has about half the R-value per inch as closed cell.
I’m trying to get ready to do a closed/unvented roof assembly/cathedralized ceiling/conditioned attic with cell foam retro install with polyiso boards below the rafters. This is in zone 5. Starting with no insulation apart from the structure/roof/wood itself.
Is there any reason to be concerned with having 1-2 inches of airspace between the closed cell foam and the bottom level of rafters? Would it be less risky or better to fill the last bit with either all closed cell down to the rafter level or use another insulation like open cell to fill the last inch of space, because it would be impossible to get flat or push the boards flat over bumpy closed cell? I understand the cured spay foam surface won’t be perfectly flat, and won’t be able to coordinate applying the boards first and spraying full area in between. I would prefer to know that the air gap won’t hurt anything, and can’t think if any reason for moisture or other issues, but it would sort of be a double vapor barrier with air in the middle of the closed cell and the polyiso boards.
Layers:
roofing shingles [existing/in place]
black roofing fabric/membrane [existing/in place]
modern plywood sheeting [existing/in place]
irregular old wood planks with ~3/4 thickness and 1/2 gaps between 4-5 inch wide pieces. [existing/in place]
6”x2” (actual) deep rafters, irregular spacing [existing/in place]
closed cell foam (4-6 inches tbd) [new / plan to add]
air gap possible (0-2 inches) [?depends on advice, new]
polyiso (2″ thick foil towards roof?) [new / plan to add]
polyiso (2″ thick foil side down) [new / plan to add]
strapping/furring strips (16inches on center air gap between) [new / plan to add]
fire rated drywall [new / plan to add]
paint on drywall [new / plan to add]
my calculations:
Minimum R Value at Rafters: 0.5 + 6 + 213 + 0.5 = 33
Maximum R Value between Rafters: 0.5 + 56.7 + 2*13 + 0.5 = 60
Here’s a good overview for those coming to this discussion late:
http://buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting/view
I strongly recommend downloading the PDF and reading carefully if you’re considering roof/attic insulation.
Back to your question.
Overall, I think your reasoning is sound. You’ll have good insulation above and a tight layer below the rafters. Minimal air should get into the small cavity between the layers of insulation so moisture concerns are minimized. There are a couple possible concerns. One is that thermal bridging at the wooden members could cause them to be cold enough for some condensation. For this reason, if you’re going to spray foam, I’d cover those as well so there is no exposed wood. If any gets on the face of the rafters, that can be scraped off so that the polyiso can be attached flush.
The second concern is raised in the attached link – potential ice dam issues of the totally unvented roof assembly. Buildingscience.com prefers under-shingle venting to keep the roof cold when you’ve got high snow-load climates. It’s something worth considering if you’re in that type of climate. For safety’s sake/peace of mind, even in a more moderate climate, I might want to implement a scheme like that. This could also save you some required spray foam thickness. So ideally, under your layer of irregular old wood planks, you’d attach nailers to the rafters, then install a layer of polyiso (between the rafters). This would form an air channel between the roof wood and the insulation layer. You’d then vent this from the bottom at the soffits and up to the ridge.
Under this layer of polyiso, you could spray foam as much as you could get in, then continue with the construction as you described. You’d still have a small air gap between the bottom of the foam and the polyiso as you noted because of the irregular surface of the foam, but now you’d have as much insulation as possible above so the chance of temperatures falling below the dew point are low.
Previously, I was feeling reassured by BA-1312: Application of Spray Foam Insulation Under Plywood and OSB Roof Sheathing and BSI-063. I had been planning to have the install go ahead with ccSPF directly against the lower roof deck surface filling the entire space. The foam installer I am most likely planning to contract with would be using Gaco 183M ccSPF.
My building has no soffit or other lower level vents- the gutters and roof edge are directly against the wall, only a ridge vent which was perhaps arbitrarily installed by roofers the previous owner hired. Side note: had been wondering if the ridge vent, even with ccSPF directly below, might help any vapor/moisture to diffuse out, like a Vapor Diffusion Vent in BSI-088: Venting Vapor, (although BSI-088 mainly pertained to roofs with insulation boards on the top side). And generally if the plywood would have some ability to dry outward/upward if moisture does come past the shingles or black roofing paper/fabric?
If I should I be concerned with keeping the airgap, it sounds like trying to keep/make a vented roof instead of going unvented. I’m a bit surprised and confused by this suggestion. If there were an airgap between the space below the wood and above the insulation board, adding shingle vents and the potential cold air seems like me to be a higher risk than the direct closed roof approach that building science seems to have tested. Joe L. did his roof this way according to BSI-063. One concern would be high snow loads on cold days where the snow doesn’t melt fast enough, but hopefully it would fall on it’s own due to steep enough pitch since I think I have a “simple roof” with enough pitch.
Also, as I head towards hopefully finally setting a date, and prepping, I was hoping to review some advice/articles on how to deal with irregular areas like chimneys, doors, the edges, etc. in prepping for a SPF job. Seen some advice on using rockwool and sheetmetal around flues, etc. But, as I try google and building science, still have questions on whether I’ve considered everything correctly.
For example, I’m planning to switch a water heater that was in the attic to a direct vent water heater. Almost overlooked that and not one of 3 well-reviewed insulation installers that I received estimates from pointed this out, although atmospherically vented heaters were mentioned in the contractor’s contract boilerplate for the one I plan to use. Their rep would have advised ocSPF on a roof deck though…
As I head to finally getting something done, I need to decide:
Am I forgetting anything important details to address first, or do I need to make a major change to the plan?
Should I insulate to ~ R-35 skip the polyiso and allow thermal bridging, then maybe install polyiso in 15-30 years with a new roof, or give up 4 inches of attic space and insulate to ~ R-61 now?
Thanks for the references for the Buildingscience.com articles.
I used to always recommend the direct spray foam-wood treatment but got so much pushback from builders, code officials and even foam installers, that I’ve grown conservative and now recommend a more conservative approach with the air-gap and soffit-to-ridge ventilation. That said, there’s more than enough evidence to prove that the direct-spray application is fine.
I would advise talking with your contractor and the local code enforcement officer to ensure that they’re on board with that. It couldn’t hurt to have printouts of the BSI articles supporting this application that you can leave with them.
I should note for others – BSI-063, shows that the straight application of foam under the roof was inadequate due to thermal bridging and low total R-value. Lstiburek went back and added 4″ of polyiso board foam on top of his roof. I tried to get my roofer to do this and they refused, claiming there was no way to attach the foam and roofing material. Unfortunately, I didn’t have BSI-063 at the time to show them how it’s done!
Your specific case is complicated due to the difficulty in venting under the deck. But there are solutions. And with the application of spray foam under the foam board creating the ventilation channel, you remove the concern of air getting into the living space since you’re sealing it all on the outside. As noted above, you can get away without the air gap but you really want to do something about thermal bridging, whether it’s foam board across the entire interior or exterior.
Here’s some of the arguments that I’ve heard from contractors against direct foam application to the underside of the roof sheathing:
Personally, I don’t subscribe to these opinions. While it is true that the sheathing will be glued to the foam, the point of the foam is greatly reduce the risk of having to replace the roof in the first place. Quoting Lstiburek “The old board sheathing was in great shape. I had all that closed-cell spray polyurethane foam underneath the deck for 17 years and nothing rotted. No surprise there. No roof leaks, no problems. No air leaks from underneath, no problems.”
Regarding chimneys etc, the consensus that I’ve heard is sheet metal and rockwool. This is another area you’ll want to consult your building official. If you don’t do it “by the book” and you have a fire, the insurance company could deny your claim if you do anything that can be shown to go against building code. If you consult with your code officer as you go, then the final approval will be much easier because, in essence, they will have had a stake in the project. It would be hard for them to deny your permits and approvals if they themself told you how to do it.
If you go direct vent with the water heater, if it’s condensing and uses plastic vent pipe, that’s a low-temperature application and they should be able to spray foam around it. But again, consult the building official. If they say you need a metal collar and air gap, then do it their way. Air sealing then becomes a bit harder since you’ll need fire-rated caulk between the flue and the collar, but it’s certainly not insurmountable. Just requires more care than just spraying the foam and letting it fill all the gaps.
As to your final question – if it were my home and I had the option of doing it now or later, I’d do it now because I’d want to enjoy the benefits of the added insulation, improved comfort and lower utility bills. If you don’t do it and you have problems, you’re going to kick yourself.
I have a completely different question now (multiple projects going on in this house). I am going to be installing a folding attic staircase. The instructions are to mount it so that the underside (room) face of the staircase door is flush with the finished ceiling. The stair case is going to be well insulated on the attic side with a Battic Door cover. But I’m thinking about offsetting the staircase deeper within the joist framing just enough so that a piece of foam board could be attached to the underside (ceiling side) of the door to provide some extra insulation and to improve the appearance of that plywood surface? It could be argued that this is unnecessary if the staircase is well insulated above in the attic. It could also be argued that whatever is attached to the underside of that door would have to be beveled at the hinged end in order not to interfere with the hinge when the door is in the down position. Are there other reasons besides these two why I never see anyone suggest or report on trying this? It is probably the sheer cosmetics of that plywood surface (and the rounded bolt heads that show on its surface) compared to the texture of the rest of the ceiling that has me thinking about this in the first place.
While you didn’t ask, I’m partial to other insulation kits for pull down stairs. I use the Essnrg.con setup. Best I’ve seen by a mile.
Second, while expensive, the Rainbow attic stairs are the only one I found that has a positive seal and looks great so you wouldn’t have to muss around with the other things that you mention. It is worth looking into.
The more I think about it, it seems that I’m probably overthinking on that question of recessing the staircase frame so that it is not flush with the rest of the finished ceiling. The rest of the ceiling in the rom has a swirl style finish coating. I can probably coat the underside of the staircase to look something like that. I’d have to recess by at least an inch to get any significant R factor from a foam board on the underside of the staircase door. Then I would have he hinge issue and that probably wouldn’t help the cosmetics either. Looks like you heavily favor, though, the essnrg insulation kits. I came across the Rainbow staircase once, but didn’t look at it closely. I will go back and look at it again to find out about their positive seal. I have already bought the staircase and the Battic insulation kit; they’re going to be installed in a couple o days. Do you have any experience with the Battic insulation kit in particular?
I had some clients who used the Battic system a long time ago so I’m not sure if it’s representative of their current offerings. At that time they were fairly flimsy more like a fabric cover with a zipper and some insulation but not terribly sturdy.
I’ll see after the Battic hatch is installed whether I want to reinforce the box on the attic side with something a little more solid. What attracted me to it is that they spec it to have an effective insulation level inside of R50. The question will be, though, how well it seals around the edges.
Sounds good, they must be improving it. Please post your experiences with it after you’ve had it in for a bit.
Thanks. I’ve never had occasion to try it myself, so I wasn’t sure about how careful you had to be when pulling the two sides apart to make sure up get a split down the middle. Sounds like if you’re a little careful about how you start it, the split should remain fairly true.
I see all the videos and advice about splitting fiberglass batting when you have electrical wires to go around in a wall. My question is: are standard fiberglass batts made to split in the middle by just pulling the two sides apart (without cutting), or is there a danger of not getting an even split in the middle.
Usually the splitting is through the batt – parallel with the face. In that direction, it pulls apart really easily. I think the strands must be oriented so that the batt almost forms many sheets because it comes apart so easily in that direction. In the other direction, you need good shears or razor-knife.
Thank you for all of the advice! It’s been quite a process with this house. Sometimes we get quite discouraged and other times it seems almost worth it 🙂
Hi Ted –
First of all, awesome site. I’m really grateful to you and some of the other high-quality building science blogs for the information you provide.
I own a 2800+ sq. foot ranch home in eastern PA. It was built in 1950 and has a slab foundation (no basement, no crawlspace). Last winter was very cold, both outside and inside. After reading a lot, speaking to multiple contractors, and having an energy audit, I decided that the 2 big items to get taken care of would be the HVAC system and the attic rework. The HVAC is taken care of (that’s a whole other entertaining saga), and now it’s time to deal with the attic. The attic itself is pretty accessible — there’s room to work and there are floor boards running down the middle portion (where it’s actually high enough to stand). There are a few layers of attempted insulation up there including very old batts, some old blown cellulose, and some less-old blown fiberglass. However, judging by the many cracks and holes I’ve found, no attempt was ever made at air sealing. This is issue #1. Issue #2 is, I suspect, airflow. There are 2 fairly large gable vents at either end of the main portion of the attic. There are, however, 2 smaller sections of attic that extend beyond. These sections sit above the (unventilated — that’s also on my to-do list) bathrooms. There are no gable vents in these areas; I don’t believe there are ridge vents either and there are definitely no soffit vents.
This brings me to my ultimate question of… what the heck do I do? Given the size of the footprint of the attic, the fact that there is pre-existing insulation to work around, and the floorboards, I have real concerns about a contractor’s ability to do a sufficiently thorough job sealing up the attic. It would seem, then, that the only viable solution would be to encapsulate the attic with closed-cell foam. Do you have any other suggestions? Are there potential issues that I’m not considering with spray foam in this style of house?
Thanks again.
Hi Ted,
I found your website while desperately searching reasons why it is raining in our attic. We seem to be getting conflicting advice, so I’d appreciate an unbiased opinion.
We live in the Boston area, and we purchased a 1970s hip roof brick front colonial. There was mold in the attic that the sellers had remediated. After we purchased the home (about 3 months ago), we had an energy assessment done. Per the recommendations, we put on a new roof and installed a new ridge vent and numerous soffit vents and proper vents, and had cellulose insulation blown into the attic (we were told that the attic floor would be air sealed prior to the cellulose blown in).
There is a persistent smell of mold on the first floor toward the front of the house, so I had a mold inspector come in. He immediately went to the attic and showed me that the underside of the sheathing was wet, and the roof nails had water dripping off! He explained that the cellulose insulation wasn’t working, and that the attic ventilation created negative air pressure inside the home. The attic sucked up all the moisture from the house; in turn, the house was sucking up air from outside, and moisture was getting into the walls as a result, and creating the musty smell. He recommended taking out the cellulose, sealing the entire attic, including all the vents, with spray foam, and said that this would take care of the odor issues downstairs.
Up to now, everyone we talked to stressed the importance of attic ventilation (which in our case isn’t working right now). This inspector recommends the opposite – sealing all the vents in the attic – which on some, probably irrational, level, scares me. What if some moisture gets in – how would it get out?
Do you have an opinion whether this could work? Or whether the idea that an attic is creating negative pressure and sucking air and moisture into the house and creating smells is sound science?
Thank you so very much!
Glad you have the presence of mind to be doing your research because if you don’t deal with the serious moisture problem, you’ll be due for another expensive roof replacement before long!
Here’s the way I would approach the problem.
First, like the mold guy did, I’d go up to the attic and see where the moisture was accumulating. Is it everywhere or restricted to some location? In almost every situation I’ve seen like this, there’s a bathroom/shower underneath the area of worst moisture in the attic. Then, when I look closer, I find that the ceiling above the bathroom wasn’t sealed properly or worse, the bath fan is leaking/blowing humid air directly into the attic. The other culprit could be recessed lights in the bathroom ceiling. They almost always cause attic problems because all the super-humid air from the bathroom just moves up through their housing and into the attic. No matter how much ventilation you have, you’ll get moisture problems from this type of construction.
So, assuming the moisture is located in a certain place of the roof, I’d have someone go up there, probably with a leaf blower, and clear off the cellulose (temporarily) from the area under the moisture problem. Then I’d look at the floor (i.e. ceiling of the room below) and look for holes, light fixtures poking through, anything where air could move from your home up to the attic.
I would not do any sort of remediation work until I discovered exactly how the moisture is getting up there. From what you tell me, your intuition is correct – you want to keep the ventilation. It sounds like your mold guy might want to find a new line of work. In order solve mold problems, you have to know the science of moisture movement and be methodical in finding the source of moisture. Moisture, as you may have gleaned from what I’ve written, is the source of most evil in homes 🙂
Once you find the source of moisture moving up to the attic, the solution is easy – plug up the holes in an approved manner. If you have recessed lights, one can make air-tight boxes out of sheet rock that are sealed above the fixtures. Or, you can replace the fixture with a super-efficient LED fixture that looks like a recessed light but seals air-tight to the ceiling. That’s my preference since the entire fixture will cost less than having someone build a box around the existing recessed lights. Plus, they’ll pay for themselves in no time because they’re so much more efficient than standard flood lamps.
If the problem is a bath fan, that’s easily solved by proper ventilation and air sealing around the fan where it goes through the bathroom ceiling. For some reason, I’ve never seen a bath fan properly installed where it’s air sealed to the sheetrock ceiling. It’s a trivial matter to air seal it and it reduces one of the biggest air leaks from the bathroom to the attic.
Sometimes the problems aren’t quite as obvious. You might have a vent pipe going up through the wall from the bathroom and out your roof. This can be a source of moisture so it should be foam sealed.
An even more tricky problem are the bathroom wall framing members. With the cellulose moved, you might see the outline of the bathroom where the 2×4’s protrude into the attic. Between the 2×4’s and the sheetrock of the walls, there are almost always gaps, sometimes substantial. These can be sealed with foam. I fixed the exact problem you described with just a few hours of sleuthing and a couple cans of spray foam. It’s not rocket science but it does require some good reasoning/sleuthing skills.
Thank you so much for responding Ted.
I’m curious: as I was reading your articles, I thought you would agree with the approach of spray foaming the entire attic floor, thus air sealing and insulating in one step – or even insulating by spray foaming the eaves and sealing off the vents – why not in our case? I totally came around to the idea of sealing off the vents after reading 🙂 now I’m all confused again.
Our bathrooms have no exhaust vents at all right now – we do plan on changing that eventually, but right now I think whatever moisture is coming into the attic, it’s doing so through the ceiling or around the framing there. We don’t have any ductwork or recessed lighting either.
What do you think about the idea of the attic sucking air and drawing moisture into the house? I’m a little bummed because I was hoping we’d find the source of the moldy smell in our main living space, but the mold inspector thought the odor was a result of the attic issues. Is that total B.S. or do you think there’s something to that?
Finally – whom should we be working with on these issues? I think you wrote you’re in the mid-Atlantic region, but do you know of any reputable consultants/engineers/companies who do this type of work in Massachusetts? I just want to get this house working!
Thank you very much for your time. It’s really invaluable to hear an unbiased opinion from someone who has no agenda.
If I were starting from scratch, I would go the foam approach, probably on the attic floor and leaving the attic itself ventilated.
As to tracking down the moisture problem – now we’re getting somewhere! If you have no exhaust vents in the bathroom, all that moisture has to go somewhere. Humid air is lighter than dry air, so it float up. Plus, it’s a very tiny molecule so it easily moves through the tiniest cracks.
During the winter, think of your house like a big chimney. Warm air moves up from the lowest levels, like the basement, up through the house, into the attic, and hopefully out. You’re probably thinking: “if air is moving out, there must be some coming in” – this gets to the observations about the attic sucking air. So there’s some validity to that argument. However, that still doesn’t explain why your house has odors. Pretty much every house has this type of air movement. The taller the house, the more this occurs. But not every house smells, so you still have to discover why. Nor does every house have attic moisture problems.
Based on what you observed in your first note, it seems like there’s two issues, at least. If ducts don’t go through the attic, which might suck in odors and distribute them throughout your home, then I have to surmise the odors on your first floor come from something else. What’s under the area that smells the most? Is it definitely a musty/moldy odor or could it be something else. Another reader reported a nasty odor in their home and that reminded me of the mice problems I have every winter. That’s a pretty distinctive, nasty, odor. I mention it in case your odor isn’t just a simple mold-like odor. It’s something to think about.
Regardless, I think you should look below the room where the smell is the worst. Or into air ducts (do you have air ducts/furnace?) There’s got to be a logical explanation.
In the worst case, you may have a water leak in the wall where you’re smelling mold. I’m think this is unlikely because usually smells don’t come through walls – you generally need air movement to carry the odors. For example, when I bought my house, I learned the hard way that my sunroom wall was totally rotted out. I never smelled anything until I poked my finger through the wall and found the entire framing rotted out!
So let me know what’s going on under the smelly room and we’ll see if we can track this down.
By the way – did anybody who came in have a thermal imaging camera? Most energy auditors these days travel with one as it’s an essential tool for finding air and water leaks. I would have felt blind without mine when I did inspections. In MA, you should have no problem finding a good building science person if you need to have someone come in. Your area has some of the best in the world. I’d ask around to see if trade professional (insulation contractors, builders, township inspectors) can tell you who the best trouble shooter is in your area. You’re looking for an energy auditor or building science person who specializes in tracking down moisture/mold issues.
There are also some trade organizations. The Building Performance Institute is one place to start. Try this link. Honestly though, so many people are BPI certified these days, that the certification is no guarantee. Your best bet is really to ask around.
By the way, I Googled the Boston area for thermal imaging professionals and this guy came up:
http://www.sawyerinfrared.com/welcome/residential_ir_boston.html
He’s the type of guy you’re probably looking for.
Thank you for explaining everything. I’m not in the building trade, but this stuff is truly fascinating!
We’re having a supervisor in the company who blew in the insulation come in tomorrow to see if they had air sealed the attic floor under the blown in insulation, as they were supposed to per our contract. I wish I had done this research before we had the cellulose put in, as I would have probably gone the foam route!
So the odor issue: it’s definitely musty/moldy. It’s strong enough that when I’m coming down the stairs from the 2nd floor, as soon as I get past the first floor ceiling line, I can smell it. Not at all a dead mouse smell. No duct work in the house – no A/C; and the heat is baseboard.
The smelly rooms are in the front of a very typical 1970s brick front colonial – there is a foyer with a slate floor and two coat closets (the coats in the closets definitely take on the smell too) and two rooms on either side with hardwood floors that we put in (flooring contractor didn’t see any issues with the subfloor). There is an unfinished cement basement underneath the entire house that has a bit of a musty funk – it was awful in the summer but we stuck a dehumidifier down there and are constantly running it. It’s still not ideal down there, but the smell is a lot better. The strange thing is, both the kitchen, which is in the back of the house, and the family room, which is on the side of the house, also sit on top of this basement, and there’s no odor at all in either of those rooms.
The house sat unoccupied or barely occupied for a couple of years, and it was owned by an older couple who didn’t do anything to upkeep it. It’s completely possible that there may have been leaky windows. We did switch out most of the windows in the house, but we used replacement windows, so the contractor didn’t open up the walls – just popped the new windows inside the existing framework. When we did the roof we installed new gutters that are getting water away from the house.
We do plan on ripping out the slate floor in the foyer and replacing it this winter, so I’m hoping we’ll come across whatever is causing the problem then. I am hoping we can do without opening up all the walls, but I am getting pretty desperate to fix the smell, so if changing the floor and subfloor doesn’t fix it, I might just take a saw to the drywall 🙂 I know it’s impossible to diagnose the issue remotely, but if you have any guesses I’d love to hear them. And I will definitely check out the links that you had sent, thank you!
Great discussion. Troubleshooting from a distance like this is tough but it does help others learn from the discussion as we work through the possibilities.
You’re not the only one learning after the fact. It seems like every time I’ve had a project/renovation done by a contractor, when it’s complete, I regret not having taken a different approach. I did the same thing with my attic and wish I’d done foam instead. No I have 16″ of cellulose and every time I have to crawl around the attic to fix something, I’m cursing!
Glad you’re not suffering from the dreaded dead mouse. That can be unbearable. But musty/moldy isn’t much fun either.
A damp basement definitely doesn’t help things. Glad you put in a dehumidifier. It’s also very possible that the moisture from the basement is working its way up through the house to the attic causing the condensation problems. When the insulation contractor comes out, have them check for any places air might be coming up from the basement to the attic. In many homes, there are various chases through the walls or around chimneys which run the full distance from basement to attic. These should be sealed at their entry point in the basement and at the attic if possible.
Is it possible that the rooms that don’t smell have better ventilation so the musty air gets flushed out more often? For example, something as simple as using the kitchen entrance to go out to the car can be enough. And, if the rooms up front rarely get fresh air, smells can build up. It could also be floor construction – one area could be leakier than the other, allowing more basement air up. It’s also feasible for some areas of the basement to be damper than others, leading to different levels.
Since the basement is clearly one issue introducing unwanted moisture – you shouldn’t have to run a dehumidifier constantly, I’d want to determine why it’s so damp. There are a few common issues leading to wet basements:
1 – high ground water levels. Water or water vapor literally seeps in through the floor and walls
2 – Inadequate gutter/downspout/roof drainage – downspouts should direct rainwater quite far from the foundation – the further the better.
3 – Improper grading around the perimeter of the house – water should drain away from the foundation
Items 2-3 are the easiest to analyze and deal with. When it’s raining out, walk around the house and check to see if the gutters and downspouts are doing their jobs. You shouldn’t have any water near the foundation because that will percolate down through the soil and saturate your foundation walls. Most foundation walls are very porous, allowing lots of moisture into the house.
The first item is hard/expensive to deal with. If you’ve ruled out items 2-3 and water just seems to seep into the basement due to a high ground water content, you may want to have the basement waterproofed. In the long run, this can be less expensive than running the dehumidifier constantly and dealing with mold and rotten roofs!
Hopefully, the basement is not finished (i.e. no sheetrocked walls etc. along the foundation). If the foundation walls are easily accessed, then waterproofing can be done in a variety of ways. Anything from waterproofing paint to spray foaming the entire perimeter walls and coating the floor with a sealant. There are also systems where they cut out a trench around the perimeter of the floor and install drainage channels. Personally, I’m not a huge fan of that approach because anything that lets water drain down also lets water vapor come up. It also provides an easier path for radon to come up from the ground and into the house.
One of my clients had a similar dank basement issue and went the route of the spray foam and loved it. It went from being a cold, damp space that they hated to a warm, dry space. It’s one of those things that you put off for years because of inconvenience and expense, then after you do it you kick yourself because it’s so much better! The nice thing about spray foam is that it’s much more foolproof than other methods. Waterproofing paint can literally blow off the walls, having to be redone every few years. With foam, they spray it on, it locks into all the nooks and crannies. It insulates really well. It pretty much prevents moisture from getting in. But, you do have to follow local building codes since it’s considered a fire hazard. Some codes allow coating the surface with a fire retardant. Others require adding a sheetrock wall, so it becomes a bigger project. Since you’ve just moved in your home, if you plan on being there for many years, it might make sense to go all the way, insulate and finish the basement like this.
This is getting a bit afield of the original discussion but I’d be remiss in any discussion of basement finishing to not mention what not to do. Do not, ever, insulate a basement the way many contractors do – they frame out a wall with 2×4’s, filling the wall with fiberglass, then staple plastic to the inside of the wall framing, then add sheetrock. This traps the moisture inside the plastic and rots out the wall framing. It’s virtually guaranteed to rot out and it will have to be completely redone. Especially if you already have a damp basement situation.
One more thing – since you’ve got a fairly serious moisture problem in the attic, and the show has to be contributing to it, I strongly recommend opening the window for 15-20 minutes after every shower to flush out excess moisture. I’d say to crack it open during your shower, but that would get mighty cold this time of year.
I own a two story home in Maine (I am the second owner). The outside walls of the second floor are not at full room height, so the first few feet of the ceiling around the perimeter of the second floor rooms follows the roofline before the attic space above the center of the rooms begins. A cement block chimney is located a couple of inches inside one of the outside walls. On the second floor, a closet space was created around the space occupied by this chimney and a metal heat duct that comes up right alongside the chimney from the basement furnace. The interior of this closet was never finished off, so I can see and touch the chimney from inside the closet. Since the chimney is right next to the outside wall and outside walls of the second floor are not at full room height, the chimney is actually going through the roof in this general closet space. The closet space is wide enough to include a couple of feet of flat ceiling to the right of where the chimney is going through the roof next to the outside wall. As I stand inside the closet and look towards the outside wall, I can not only see where the chimney is going through the roof, but I an also look straight out and see the top plate of the outside wall and the underside of the roof under the eave beyond the outside wall.
In general there is insulation in the walls of the house, in the attic, and even between rafters in the attic since this is not a very old house. However, in this particular closet area, I don’t think the insulation and weather sealing is as tight as it should be. I would like to have this general area inside the closet properly weather sealed and insulated so that the interior of the closet is part of the interior heated envelope of the house. I want to seal the inside of the closet from the roofline, the outside wall, and the chimney itself. I can put up a partition wall inside the closet to separate the weather sealed parts surrounding the chimney from the usable closet space. Whether the latter portion wall is put up or not, I want the weather sealing to be done because I intend to have a heat pump air handler installed in this general closet area on the side that has the flat ceiling and which is next to the wall on the interior side of the house.
I am trying to get an insulation contractor in to do this job, and am assuming that they will have to use foam to get to the spaces on the outside perimeter of this closet space (outside wall, eave, roof line). I am looking for advice about proper treatment of vapor issues that could arise when trying to weather seal and insulate this peculiar spacial situation and given Maine climate. What type of foam, does there need to be a vapor barrier, on both sides, on one side, on which side of the foam? Besides the wall and roof surfaces on the outside of this closet area, what should be on/in the interior wall partitions that separate the usable closet space that is inside the heating envelope of the house from this chimney cavity? What else should I be looking for?
I know this may be hard to answer without seeing the space first hand, but I am hoping that there is some wisdom from your experience that can nonetheless be applied. I have an opportunity to do things right that I don’t want to pass up here. That new air handler has to go in that closet, but I want its heat to stay in the house.
Well, you do win the award for most complex question 🙂
I would probably frame out a wall around the chimney to create distinct interior/exterior areas of the closet, fireproofed and insulated on the chimney side with something like mineral wool. On the inside, make it a normal wall with sheet rock, perhaps a little thicker than normal. Your local fire codes should be consulted to ensure everything you do around the chimney is “to code.”
Once you’ve dealt with the fire safety issues and created an air sealed and insulated, interior space for the closet, your moisture concerns would be the same as for any construction in your area. Mainly – you want to keep warm, humid air inside your house away from cold spaces, like the attic or the now hidden space behind your closet, so construction details are the key thing. Air carries far more moisture than goes through the wall materials, so ensuring an air-tight seal is your key concern, but you want to consult your local with your local building official and do what he/she says as far as vapor barriers.
Thanks for the award and the advice. You have confirmed my intuition about separating the interior usable closet space from the chimney cavity itself by interior wall partitions. So regardless of what is done to insulate or weather seal the outside of the chimney cavity (the outside wall and roof line), it would be mineral wool rather than foam that should be used inside those interior partition walls inside the closet. I assume that the vapor barrier (plastic sheeting) should go on the inside of those interior partition walls (on the face the partition stud framing – between the mineral wool and the sheet rock). I’ll rely on the insulation contractor to advise me on what would be best thing to do on the outside wall and roof line of this chimney cavity, and the fire codes. There is no possibility of doing anything from the outside of the house (except the chimney flashing on the roof). This is a tight area to work in inside this closet. It is tough to retrofit now. Would have been better if it was done right when the house was built.
Vapor barrier, when used, is typically as you note.
As long as the area around the chimney aren’t leaking now, I wouldn’t mess much with them. If they leak air but not water, which it sounds like the way you’ve described, you may want to leave it as-is and just consider the area well ventilated. I say this because if you try to air seal this space too, you’ll create a “dead air space” – meaning the air can’t go anywhere. The problem with that is that the roof and exterior walls will be very cold in the winter and the moisture trapped in the space will condense on those cold surfaces. So, other than ensuring that the exterior is water tight, I wouldn’t play with it or you might have an unintended consequence.
Thank you again. I think that makes a whole lot of sense. I will be interesting to see if the insulation company evaluator advises the same thing. At least the interior partition walls would be a little easier to deal with and get to.
A little pushback here may be needed here to clarify something. You are worried that moist air in a well sealed dead air space would have no where to go and might condense on cold outside walls. But if the outside wall was foam insulated (as opposed to some sort of fiber insulation), why would the inside surface of that outside wall (that is the foam surface facing the interior of the house) be cold? Isn’t the whole point of the insulation on the outside wall to prevent that? If the outside wall is foam insulated and the inside wall partitions on the other side of the chimney cavity have a vapor barrier as well, then I agree that moist air in the dead air space would have nowhere to go. So there are a number of factors going into the decision I have to make. Leaving the outside wall alone all together if I am going to insulate and seal the inside partitions is one approach which as you suggested avoids creating a dead air space that cannot breathe in any direction. With the opposite approach – sealing the outside wall with foam, it could be argued that no insulation or vapor barrier is need at all on the inside wall partitions that separate the closet space from the chimney cavity. I want to make sure, though, that none of the rationales that I have to consider are contradictory. In any option that involves foam on the outside wall and roof surface, the notion that moisture could condense on those outside surfaces – even if I also sealed the interior wall partitions (which admittedly may at that point be overkill), seems to contradict the premise of why the foam would be applied in the first place. Can you further clarify this point? I thank you for your input.
Thanks for asking for clarification, I may have misunderstood.
If you only air seal and insulate the exterior walls, then that inner space will be warmer and condensation is less of a concern as long as you don’t further close off the space with the walls making an enclosed closet space. The concern is how much of your inside warmth can reach those exterior walls to keep them above the dew point temperature where condensation would form.
During the winter, I would often get calls from folks who had cold walk-in closets – sometimes cold enough for condensation to form on the drywall. These were usually inside well insulated walls. Since they were cold, the homeowners would close the door to the closet so that their bedrooms wouldn’t get cold. So the closets got even colder. The reason is probably obvious to you – no heat supply for the closet. Without an active heat source, the space would only get a trickle of heat from the bedroom, and, even though insulated, would lose more heat through the exterior walls. I’m concerned that your closet/chimney/attic space, even if insulated, would fall into this same category of problem. Yes, it would be inside the insulated envelope of the house but it would likely get cold due to lack of active heating. Depending on the humidity level inside your home and the outside temperatures, it could get cold enough to create a condensation problem. That’s the basis of my concerns.
For this reason, any time there’s a dead air space adjoining exterior walls that appears to lack active heating/conditioning, I get concerned.
I’ve seen several homes that ended up with fairly ugly moisture and/or mold problems where they did the “right” thing by foaming the back side of short walls like this (between roof spaces of the sort you describe and living spaces) but then the insulator, thinking they were doing the right thing, foam sealed all the air entry/exit points in the now dead air space. Having seen these issues, I’m very conservative in my recommendations and avoid dead air spaces whenever possible.
I think I see what you are saying now and what I was unconsciously overlooking in my original thinking. I’m going to paraphrase to see if I’m understanding it. I subconsciously presumed that a real good foam insulation on that outside wall would all by itself guarantee that the inside surface could not get cold enough for condensation no matter how cold the outside air was. The flaw in that logic is that the insulation does not guarantee an absolute temperature on one side; it really is only creating a greater differential between one side and the other. The other thing I evidently was overlooking is that having a heat source matters. If you turn off all heat sources inside a house and walk away forever, that house is eventually going to cool down and maybe even get cold on the inside in the winter (depending on just how leaky it is, how long the outdoor air stays cold, and what you define as “cold”, and solar insolation). – even if it has good insulation. The insulation R factor affects how cold the house will get or how long it takes to get cold, but it doesn’t guarantee that it will never get cold. And if it is super cold outside, even though there is a big R differential between the two sides of the insulated wall, the “warmer” side could potentially come close to dew point. If you have a big differential between inside and outside just on the basis of insulation R factor and you keep providing some heat on the inside, you can actually increase the net differential between outside and inside temperature and stay away from reaching the dew point on the inside surface. The better the foam insulation R factor, the less heat it will take to keep the inside surface above dew point. And this comes to your point about the closet getting cold because it is cut of from the heat source, even though the outside walls were insulated.
Now for the sake of argument, does it logically follow that If the envelope of the house is well insulated and sealed, and I keep all interior spaces of the house well heated, that I wouldn’t need a vapor barrier inside the house to prevent structural from water vapor even if the air inside the house is humid? I know that statement was presumed a lot, and that we put in vapor barriers because you can’t always be so presumptuous. In the north, that is why we put the vapor barrier behind the sheet rock and on the interior face of the wall studding so that the moisture doesn’t go any further behind it and into the wall structure – especially if there is an insufficient heat source inside. As you point out, even that doesn’t protect the sheet rock itself if the air is moist and the sheet rock is cold.
To restate your position, my best choices are either to seal and insulate that outside wall while leaving any interior partitions uninsulated, or to leave the outside wall uninsulated and seal the inside partitions around the chimney cavity and ceiling extremely well instead. The usable interior space of the closet will definitely have a heat source even with the closet door closed because that is where the air handler supplying that second floor with heat. I just wanted to make sure that there was not a significant loss of heat to the outside of the house right at its very source point. Even if just the outside wall and ceiling is foamed, does the cement block in the chimney itself not present a thermal bridge to the outside as it goes though the roof? That almost makes me prefer the choice of insulating the interior wall partitions that separate the closet interior and the air handler from the chimney cavity.
Thanks again for your clarification. Correct me if I’m still misstating anything.
It looks like you’ve got it.
On your final comment – yes, I’d put the insulated partition wall in such a way as to keep the chimney outside the insulated area for exactly the reason you mention. Plus, in the unlikely event of a fire or crack in the chimney, the wall provides an additional safety barrier.
Ted,
I recently purchased an 1887 home with lathe and plaster walls. You probably know where this question is going, and have probably answer it before. The walls aren’t insulated. I know enough to know I can’t just haphazardly blow in insulation because of moisture issues. Is closed-cell spray foam okay, since it seals against moisture infiltration?
Thanks in advance,
Chase.
The details depend upon the actual construction. Usually when it’s that old, there’s a very small cavity between the exterior wall and the inside wall. But, if you are lucky enough to have space to fill with insulation, then the question is – which side are you going to come from (outside or inside).
For example, my 1950’s home has plaster-lath walls and simple 2×4 wall construction with siding. When we decided to renovate and redo the siding, I decided that would be the perfect time to deal with the insulation. We first had cellulose blown into the walls, mostly through the exterior. Then we applied 1 1/2″ foam board and then the new siding. For my climate, this was pretty safe because the exterior foam board had about the same R-value as the insulation blown into the walls, so any moisture that got into the walls would be unlikely to cause condensation issues. In a colder climate, I would have wanted to add more exterior insulation. However, I would have been nervous to simply blow cellulose into the exterior walls without that additional layer of insulation.
You ask about spray foam – how would you have that installed? You’d pretty much have to rip off the siding and any exterior sheathing, then spray the foam to the back of your plaster-lath walls. Then reinstall the sheathing and siding. If so, that’s likely to be the best approach for most climates.
Tiger Foam has a slow-rise formula that you inject in through 3/8″ holes in the interior or exterior wall. I’ve read about “ballooning” when you inject a pressurized media into the wall cavity, but their website assures this won’t happen if you follow their instructions.
I tried that product a few years ago and it was a complete waste of money. Without a thermal imaging camera (which I DO have) it’s important to tell anything about the fill. Even with the right equipment, when I opened the wall during renovations, the fill was poor and incomplete. I’ve also seen professional injected foam jobs that were totally botched. The worst was in the wall of a friend who himself was an insulation contractor. He hired a specialist to do the job and even they didn’t do it right.
Thanks for the quick reply and the info. I was planning on rehabbing the exterior of the house next summer anyway, so coming in with insulation from the exterior sounds like the way to go. I know it’s a shot in the dark, but do you have any idea what kind of sheathing (if any) might possibly be under my siding? It’s aluminum siding so I assume it’s not original.
On that old house, it’s impossible to say since it must have been renovated since original construction. Could be wood planks if really old, or plywood if rehabbed before everybody got cheap and switched to flake board. You could carefully pry up a piece of aluminum siding to see what’s underneath.
Okay so since you do not recommend injecting spray foam, and since I don’t want to disturb the existing walls, my only option for adding insulation is from the exterior. Assuming it’s in decent shape, I don’t think it would be financially viable to demo and replace all the decking just for the sake of adding insulation, so if I do pull the decking, I would try to reuse it. Would you even bother doing all that, or would you just add a couple layers of foam board and be done with it? Also, should I add home wrap before new siding? What about the foil faced wrap, or a product like Silvercote Solarguard? I’m wondering if just doing foam board + foil would be adequate. I’m an HVAC engineer so I can run the heat load calcs and do comparisons, but I know nothing about wall construction and don’t want to do something that will cause moisture problems. Thanks again.
If your walls are 2×4 constructed or something comparable, you could do what I did which is have cellulose blown in at high density then use board foam. You’d have to install nailers to attach the foam and siding to but I’m assuming that whomever does the work can worry about the structural details. That’s worked quite well.
I wouldn’t add anything that’s moisture impermeable, like foil, out there because that can lock in moisture. You typically want something that will allow moisture to slowly dissipate. Always assume that some moisture will get into the wall cavities so it needs to be constructed such that it can get out. For the record, we’re talking minute amounts of moisture, not water leaks.
So, from the inside towards outside, you’d have:
Plaster -> lath -> cellulose or empty wall cavity -> exterior sheathing -> board foam -> Tyvek/construction paper -> siding
When done properly, injected high-density cellulose will make your walls much more air tight and sound proofed as well as insulating. Look up “dense packed cellulose” if you want to go this route because it’s hard to find an insulation contractor who does dense packed properly. Here’s a nice article describing the pros/cons of dense packing.
I read this article yesterday that gave me the impression blown in cellulose was a bad idea since there is no vapor barrier on the plaster-lath walls. http://bobyapp.com/blog/2009/06/myths-about-insulating-old-house-walls
But you say “Properly done high-density cellulose”, so I guess there is a big difference between that and regular blown-in cellulose?
I did a quick read of the linked article and it appears that the author, while well intentioned, does not have the depth of knowledge needed to comment about vapor barriers and dense packed cellulose.
Do a quick read of the building science article I linked to. the TL;DR version is: dense packed cellulose is great in walls because there isn’t a vapor barrier so any small amounts of moisture getting in can escape out through the outer walls but not good in roofs which usually have vapor barriers blocking that moisture escape.
Note however that vapor barrier usage and location varies depending on your local weather conditions. In warm, humid climates (like Florida), you can have considerable moisture drive from the outside and then the drying is to the inside because the “cold wall” is the air conditioned interior wall. In cooler climates, the cold wall is the exterior wall and moisture moves towards the cold, lower moisture area.
I should have warned however that in older homes, if your wiring wasn’t upgraded, there may still be bare or poorly insulated old wires running through the walls (so-called knob and tube). These walls should not be insulated with dense pack. The Applegate site has some great resources. Quoting from this site: “Building cavities are dense packed by inserting a pipe, tube, or hose down the entire
length of the passage. A powerful insulation blower delivers a lean mixture of cellulose
and air at about a hundred feet per second. Initially the cavity is pressurized with a cloud
of insulation. The air flows out through every crack and pinhole carrying fine particles of
insulation. The holes are clogged with insulation until they stop flowing and the cavity
fills with a loose pile. Then the cellulose chunks charging down the tube start to slam into
the loose pile and pack it. When it becomes very tight, it plugs the end of tube and stalls
the insulation blower. The tube is quickly pulled back until the tip finds more loose
insulation. The flow and packing process starts again and this continues until the entire
cavity is solid. ”
Many contractors use a different method and claim to be dense packing but this is the only approved method for retrofit installations of dense packed cellulose. Trust me, I’ve analyzed homes done by contractors who claimed their method was better.
ultimately though, if there are any concerns about cavity fill, then just do exterior board foam. That will insulate pretty well and do a lot to keep water out of the walls.
Thanks for all your great input. If I do ultimately end up pulling the exterior sheathing, what type of cavity insulation would you recommend at that point?
If it were my home, I’d spray foam it. In fact, in those places I was able to, I did foam. In the other places, I blew it full of cellulose which is the best bang for the buck.
Ted,
You answered a few questions for me last week regarding insulation and we spoke about foam board. Just to make sure I buy what you recommend, are you speaking of “Unfaced Polystyrene Foam Board Insulation”? Thanks again. http://www.lowes.com/pd_304087-210-100000050511_1z0uh9aZ1z11pq2__?productId=999973072&pl=1
Usually which used externally is what’s called Blue Board or pink board. It’s denser than the normal styrofoam that coolers are made out of. I think that’s what the link you posted is. But I’m on my phone right now and I can’t quite tell.