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Ted's Energy Tips 
Ted,
In the process of insulating my crawlspace. 2″ rigid foam in the rim joists, foamed in place, rigid foam on top of the block and on the inside wall of the the crawlspace walls, all seams taped and foamed. I’ll be installing a vapor barrier on the floor and up the walls slightly. Is there anything I’m missing? Is it advantageous at all to add rigid foam over the vapor barrier on the floor? Should I be introducing conditioned air into the space via a dedicated duct? The crawlspace is only under one 14×14 room.
Many thanks in advance!
Happy Thanksgiving!
-Andy
And a happy Thanksgiving to you!
As with your other projects, it sounds like you’ve been thorough. From what I’ve seen, there’s some debate about airflow in crawlspaces, but I think the building scientists are winning in their call to have insulated crawlspaces treated like little basements – sealed, insulated and ventilated. I personally like the idea of placing just a small supply of conditioned air into the space to pressurize it slightly. Most will leak back into the house through the floor but it will also help offset the air infiltrating around the perimeter and floor. I don’t know if any studies have really shown this to be effective, but it sounds good 🙂
As for floor insulation, the heat loss can be substantial, so laying down a couple inches of board foam can certainly help, especially when including the space in the envelope of the house.
Ted,
In regards to my vapor barrier on the floor: I plan on running it up the block walls a bit, maybe 6-8″. (They poured a footer all the way up to grade and then set two courses of block.) Should I attach this excess vapor barrier directly to the block, and then put my 2″ rigid foam over it, or can I put the foam on the walls and then tape the vapor barrier to it? The two courses of block on the inside are exposed to the outside. The crawlspace is really no deeper than grade.
Thanks again!
Andy
I’d prefer to put the vapor barrier up the wall and the foam over it so that any water vapor that escaped would tend to move through the block and out rather than inside your home. When I did a rental property with a serious crawlspace moisture problem, I sprayed foam over the vapor barrier to seal it to the walls, then kept going up from there to the band joist. In your case, you’d be using the rigid foam, but same effect.
I’ve found conflicting information on covering the block with vapor barrier, as expected. Some run the vapor barrier all the way to the top of the block, not including the rim joist, or you’ll rot it out. Others say not to cover the block with any vapor barrier because it has to dry to the inside. Albeit, slowing through the foam. What’s the verdict when it comes to vapor drive and block or poured concrete walls? Also, the back wall of the crawlspace is the opposite side of the basement wall. If I put foam on both sides, basement and crawlspace, am I asking for trouble with moisture?
Thank you!
Andy
If the block is underground, it’s wet where it meets the dirt and it will always be wet because that’s an infinite supply of moisture. So I’d cover it up without hesitation. The only concern, as I think you may have pointed out from BuildingScience.com was insulating behind brick where the moisture drive needs to be allowed to dry out or you can end up with fractures due to freeze/thaw cycles. If you’ve got a link to a building science article indicating that you shouldn’t trap moisture in an underground block wall, by all means, let me know and I’ll read through it. Ideally, you want to spray or foam board on the outside of a block wall, but that’s not usually an option with retrofits. Rim joists, I wouldn’t mind spray foaming over (I did mine) because in the winter, the air is dry and they’ll dry to the outside. However, this varies with climate and in some locales you have to be very careful about termites, so they want them uncovered for inspection purpose. I’d note that I hate the practice of insulating the inside of rim joists with fiberglass because that’s completely moisture permeable so interior moisture is almost guaranteed to condense on the now cold wood.
As for double insulating the block, it’s not really necessary to insulate either side since that’s just a wall separating two insulated spaces and the insulation on the outer walls is doing all the work. Unless I’m missing something.
-Ted
My crawlspace is only two blocks tall, and both courses are above grade, so I don’t think I need to be too worried about making sure I run my vapor barrier up the wall too high. My plan is to put vapor barrier on the floor, 2″ rigid foam in the rim joists, 2″ rigid foam on the walls, 2″ rigid foam on the floor over the vapor barrier, all sealed with expanding foam. As you suggested, I won’t put any foam on the adjoining basement wall. I have considered putting roxul in the rim joist on top of the rigid foam, but I don’t know if it’s needed. After all the insulating is done, I’ll run a 4″ duct into the space to introduce conditioned air. I do wonder if I should bore a couple 4 inch holes in the rim joist that joins the basement to the crawlspace to allow air exchange with the space hopefully being extremely tight after I’m done.
Also, you’ve been tremendously helpful with many of my posts and I realize your time is worth something. I did see where I can donate per post, but I would assume that would only be going forward. Is there a way I could donate a flat amount to you for all you’ve helped me thus so far?
Thank you,
Andy
Oh, I thought I misread that earlier. How the heck do you work in a crawlspace that tiny?
I’d skip the Roxul – that would insulate the foam, allowing the surface of the foam to drop in temperature and maybe allowing condensation to form and drip down. Not terribly likely but still, probably not worth the risk.
Thanks for your generous offer. I just checked Patreon and it’s not clear how to do a one-time donation. I’m happy to take a Paypal contribution. Here’s a direct link.
Also thanks for all the great discussions. It’s always a pleasure to work with you and others who take a serious interest in their homes.
How do I move around in a 2-course high crawlspace? I slither around on my stomach, much the same way I do in my 4-12 pitch attic! If I’m moving in the same direction as the floor joist I get an extra 9″ of headroom between joists though, lol.
A dilemma I discovered last night while working down there was on my front wall. The rim joist runs parallel to the foundation wall, so I have one big, long rim joist bay essentially. The problem is, the next floor joist is set so close to the outside band board that there’s not more than 1″-1.5″ from the edge of the floor joist to the foundation wall. Needless to say, that’s not enough space for me to get any foam board in there, much less spray foam the perimeter to seal. The only thing I can think of is to seal the small 1″-1.5″ gap so no conditioned air from the crawlspace fills that void and comes in contact with the cold band board.
Can you think of any better solutions, or am I missing an obvious solution?
Thank you!
Andy
I seem to recall having that problem in the crawlspace of the townhouse I sealed up. I think I spray foamed over the wood rather than using board foam. You can fit the nozzle into the gap and “spray and pray” using one of those semi-industrial spray foam kits from Fomo-foam. OTOH, if I were to do it today, I might just do what you said and seal that small gap to minimize moisture movement to that area. You might then want to apply your board foam to the joist since it will get really cold and might be prone to condensation.
Excellent! I appreciate the confirmation. That was my thought: seal the opening and then either on the inside or outside of the floor joist, apply foam board to eliminate condensation and cold transferring through the floor joist. If I were using a commercial foam kit (here we can get something called a Froth-Pak), I would do that: insert the nozzle and spray the best I could. But they’re over $325 for what they claim is 200 board feet of 2-part spray foam. I can buy all the 2″ rigid foam for the rim joists & walls for less than a third of that. It’s more labor intensive, but I don’t mind the work. At times I’ve thought about putting roxul over the foam on the walls and in the rim joists because more insulation is always better, right, but from our previous exchanges it sounds like I only want foam in this space?
Correct on your last point. If you added Roxul that would reduce the amount of heat that can reach the inside surface of the foam so the temperature of the foam would drop creating a condensation hazard. So I would skip that. This is why the so-called flash and method using a thin spray foam layer and then lots of fiberglass insulation is such an utter failure.
I have 2 big trunk lines insulated pipes coming from my cellar to the attic. My problem is that they are enclosed in the house and the enclosure is about 4ft X 6ft, depth maybe 15 ft. Do I have to fill this hole with insulation or can I used Styrofoam board with foam and seal the hole in the attic. I would hate it I had to fill it with insulation.
You can just seal from the attic side. The key thing is to minimize the air movement between the cellar and the attic since the tendency would be for cold winter air to get sucked down the hole and moist warmer air from the attic to go up through the hole. So foam board cut and sealed, maybe with some canned spray foam around the trunk lines, sealing the opening to the foam board. That should make a big difference and potentially save your roof from rotting out.
Hi Ted, we are currently under contract on a house built in 1964. We were told spray foam insulation was applied around 20 years ago. How do we know it was applied properly? What are the signs we should be looking for and the questions we should be asking to ensure it is working properly and not putting us at risk for health problems etc. we are a family with two very young children and scared to run into any problems! Any advice help would be so appreciated!
Some older spray foam did have VOC issues which led to outgassing of unpleasant substances. However, those issues diminish exponentially over time so after 20 years, it’s unlikely that there is anything left in the foam. I still wouldn’t want to eat it, but if you’re not breaking off chunks, it’s highly unlikely to be a hazard, especially in the attic or locked away behind walls.
The other potential issue is flammability. Some foams are extremely flammable and need to be covered by a fire retardant material or sealed inside walls. If the house has exposed foam, like in the attic or basement, it should be covered (there are spray on substances) to reduce the fire risk. In some jurisdictions this is a requirement so you’d want to check with your local code enforcement officer. They may also be able to let you know if anybody in your area has experienced issues with spray foam from the 1990’s when this home was sprayed.
Finally, when in doubt, have a professional indoor air quality professional come in and test the air. They can test for other issues at the same time (mold etc.) and may worth doing for your peace of mind.
Ted
Occasionally one room in my house gets saturated with a fine powder that’s light orange in color. When I clean it up with a wet paper towel it’s more rust colored on the towel. I think it even smells a tad rusty. Every other room in the house has regular looking dust. I’ve had Air duct cleaners look at it and they had no idea what it was. Our house was built in 1981. My concern is vermiculite. Would vermiculite dust look and smell like this.
Ted,
I’m insulating a 2′ cantilever on the rear of my house. It is for the first floor, so I’m overhanging the foundation wall. So far, I have installed blocking at the foundation wall, installed polyiso in the top of the cantilever bays leaving a 1″ air gap between the polyiso and the subfloor, batt insulation and then plywood. From what I can see online, there are lots of recommendations for installing rigid insulation on the top of the cantilever (underneath the subfloor), and at the bottom of the cantilever (just above plywood to enclose). Is this not creating a double vapor barrier?
Also, as it stands, I have been totally segregating the cantilever from the basement space and have filled with R-19. Would I be better off installing R-13 or R-15 on the floor of the cantilever and leaving the top couple of inches under the subfloor open to the basement so any warm or cool air could circulate under the floor?
Thanks in advance! You never steer me wrong!
Andy
Hey Andy,
I wouldn’t want to create the double vapor barrier either. I probably wouldn’t want to have left an air gap between the subfloor – perhaps I’m missing something there.
Typically, we want a continuous thermal and air barrier in close proximity to the inside living space – in this case, the floor that rests above the cantilever. If you leave an air gap there, there’s an opportunity for the cold air to get in between. I would have used construction adhesive around the perimeter and glued the polyiso to the subfloor then put batts under that for added R.
As for the part over the basement, do you have the option of adding insulation on the floor as you say? That would raise the floor up a couple/few inches, wouldn’t it? I’d have to think about this one. Assuming the basement is a cold space in winter, this approach would be beneficial, and at first glance, shouldn’t result in moisture issues. Is there anything more about the basement that might make it a “danger zone” from the moisture/condensation perspective that might affect the approach you take?
Ted,
I believe I did not convey my question properly. When I referenced insulating the “floor”, I was referring to the bottom of the cantilever, but not packing the full depth of the joist bay. I was thinking of rigid on the bottom above plywood, then R13 on top of that, leaving a gap of a couple inches under the subfloor above the cantilever. My thought was that conditioned air in the basement would circulate in the gap affecting the temperature of the floor above. I have one register in my basement and whatever radiates off of the duct work.
In regards to the air gap with the polyiso, I was treating the cantilever like a crawl space floor, and thought I had read on the building science site that polyiso performs best with an air gap to the conditioned side. The edges are sprayed foamed, so there’s no chance of any outside air intrusion.
I see, my mistake. Yes, a gap between the foil face and adjacent surface is recommended for maximum effectiveness of the radiant reflector. And as long as you sealed the edges, you’re good to go.
I’m still not following the basement construction. Why would you want insulation AND air circulation in the gap between the subfloor and insulation? That short-circuits the insulation, rendering it useless. Sorry if I’m being dense, I just don’t see it.
Ted,
My thought process was that the insulation would help to slow the intrusion of the outside temperature from below while allowing the basement air to either heat or cool the underside of the subfloor. But as always, you’re right. If I think about it like an upside down basement, we want the insulation right up tight to the conditioned space. My thought process was that I wanted the conditioned basement air to be in contact with the underside of the subfloor like it does in the rest of the basement. If I sealed up the cantilever from the basement, it’d be a dead zone?
Most cantilevers that I’ve seen are sealed. If there’s a unpenetrated subfloor and the iso boards formed under that, there’s minimal chance of moisture intrusion and condensation. If you leave it open to the basement, you’re providing a big cold air pathway from the bottom of the cantilevers (which are invariably poorly sealed. In fact, during blower door tests, the worst air infiltration I’ve seen has been from exactly this construction.
Ted,
I have some plumbing for an outdoor spigot running through a two foot cantilever. The plumber installed a frost-free sillcock,but obviously I don’t think that’s necessary because it still doesn’t get the valve into the warm basement. My question is how to insulate this bay of the cantilever. Should I air seal the cantilever bay with foam board and then leave open to the basement, or do I treat it as I am the other cantilever bays: foam board at the rim and under the subfloor, air seal and pack the remaining cavity with insulation?
Thanks in advance,
Andy
I think your analysis is correct based upon your description. The rest of the piping would be exposed to the winter cold and subject to freezing. One option would be to install a shut off valve in the basement and then open the spigot outside so that the water would drain out of the pipe and only the warm section of pipe would have water in it. This way you wouldn’t have to worry about how you insulate the cantilever section and could just insulate it the way you do everything else. That’s my first thought so you don’t have to worry about that section of pipe freezing up and having to do something tricky with the insulation.
Ted, you’ve saved the day yet again! On a separate note, but same project: I have ductwork that runs in these cantilevered bays. What is your opinion on insulated flex duct vs. rigid? I’ve heard things about lower velocities and cfm’s from flex based on the interior not being smooth and creating turbulence. I would only have a 30″ piece where it transitions from rigid 6″ round to the register boot through the cantilever.
Thank you!
From my experience I was told you are only allowed a small percentage of the run to be flex . It does cut down the flow . What makes the flow worse is if you do not pull the flex tight , which causes more air swirl which equals more flow loss
Flex is one of those necessary evils. As noted by Blake, it’s preferable to keep it short and tight. I’d add that you want to keep bends well-formed and as gradual as possible – the tighter the bend, the more airflow resistance.
If the duct is exposed to cold, I’d definitely want it well insulated, maybe surrounding it tightly with batts in those spaces. Also consider summer usage where very cold air will flow. Metal duct is highly prone to condensation, so it’s important to install the flex “by the book”, tightly sealing the outer plastic sheathe around the insulation layer to minimize the humid air that can get in there.
I wouldn’t have any turns in my flex. It will be a straight shot into the cantilever and will not be any longer than 3′. And this is an A or B selection. My entire duct system is 6″ round currently. I have runs that pass through the cantilever to registers above and while I’m enclosing the cantilever, I was addressing those duct runs within. If I change to flex, it will only be within the cantilever bay.
In regards to the rigid and sweating, I was considering insulating the whole interior of the cantilever box that the duct passes through with 2″ rigid and spray foaming the seams, essentially making it air tight to preserve the conditioned air inside the duct, whether it be warm or cold, depending on the season. Are there any issues with this that I’m not thinking of?
Ted,
I’m in need of your expertise once again. I’m building a tray ceiling in my bedroom. This afternoon, I just had the idea that I’d like to fill the sunken area in the middle with beadboard to create some visual interest. I cannot go over the drywall as it pretty wavy, plus the tray is not very deep and I would lose the effect. I would like to cut out the drywall and nail the beadboard to the trusses, with some added blocking as they’re 24″ on center. Would I run into any issues with this? Wood being exposed to the attic? I assume I’d want some poly under the beadboard, but would it even be useful with all the nail holes? My second thought was maybe replace the drywall with OSB so I had a solid nailing base, and I seem to remember reading something about it having a pretty low vapor permeance rating. What are your thoughts on this endeavor?
Much thanks, Andy
Sounds like a cool project! I haven’t seen too many ceilings like that so I’m going to have to answer this from theory rather than personal experience.
I’d be a little leery of cutting out the drywall since it forms a continuous air and moisture barrier with the existing ceiling. Any disruption to it would require careful sealing to ensure you didn’t create an undesirable situation.
Assuming that you are diligent in your work, and it sounds like you would be, rather than trying to put plastic under it, which would be difficult to adequately seal around the edges anyway, how about gluing some 2″ rigid XPS or polyiso foam board to it? You would install it from the attic side so that it fits nicely between the joists, and seal it with a complete bead of caulk around the perimeter as well as some zigzags along the center to minimize vibrations and strengthen the structure. For greater air/moisture control around the edges which are the expected weak points, you could caulk or foam the cracks. This composite ceiling should likely be sturdy and air-tight. I would think you could forego the blocking and OSB because there’s minimal load on the ceiling – unless you’re planning on hanging something from it, in which case you might just reinforce that location with a block in the attic, properly affixed to the joists.
How’s that sound?
Ted,
So to clarify your suggestion: you would have me remove the drywall, nail the beadboard directly to the trusses, and then from the attic side, install 2″ rigid foam in between the trusses and spray foam/air seal them in place?
-Andy
Andy, it’s not so much that I recommend cutting out the sheetrock and putting in the bead board, but it sounds like you want to go that route. If you do want to do it for aesthetic reasons, then I’d try it that way with foam and sealing. Personally, I would want to leave the sheetrock intact and would go another route for aesthetics 🙂
Ted,
Still working in my crawlspace, and while slithering around there today, I had an idea. I originally bought a bunch of sheets of 2″ rigid to put on the floor over the vapor barrier. Since my floor is not completely level, I wondered if Roxul would suit me better as it would easily flow with the terrain, so to speak. It is unaffected by moisture, and at R15, it’s slightly better than the R10 of the 2″ rigid, not to mention cost wise, it works out to be a better deal. I realize it doesn’t have the vapor impermanence of the rigid, but I will already have a continuous vapor barrier taped & sealed directly over the ground.
I feel like I may be missing something though. Do you see any inconsistencies with this approach?
Thank you,
-Andy
That is unusual, and I’ve never heard of it being done, but off hand I can’t see why that wouldn’t at least reduce the heat loss through the floor. I guess the advantage of board foam when it is possible to use is that you can still use it as a floor whereas the rock wool doesn’t.
Ted,
Not so much of a want as a need. My home was built in the early 70’s, hence 1/2″ drywall on 24″ oc trusses. It was also a foreclosure prior to me purchasing it, which means the bank turned off the power and flooded the basement due to no sump pump and high water table. The home was so wrought with moisture that you could see old water stains on the ceiling and where it had run down the walls. The ceiling absorbed so much moisture that the ceiling in the entire house sagged between the trusses, in some locations as much as an inch. With lots of mud, sanding, and flat paint, you no longer notice the discrepancies. The problem is, if you want to install anything on the ceiling, it is no longer flat. I can press it back into place with 2×4’s, construction adhesive and screws where I need framing, around the perimeter of the tray ceiling, but in the center, it’s still wavy, and there’s no way to lay any sheet good or flat stock. If I need a smooth surface, I either need to cut out and replace the offending drywall, or find a way to take the sags out of the drywall so I can go over it with wainscotting, bead board, panels, beams, etc.
I’m building a coffered ceiling in my living room and would like to bead board the ceiling in the kitchen too, with a small tray above the dining area, but am running in to the same sagged ceiling. At this point, I’m considered just ripping down all the ceiling in the offending areas and reinstalling. But I really hate mudding, taping, and sanding. Not to mention the fact that you lose the continual air & vapor barrier patching drywall in.
-Andy
Wow, that sounds like it was a real mess! I don’t envy your job.
thank you for a great site. do you have any info on why some HVAC units have a covered top
while some have mesh top , can the top be covered as long as it does as long asthe air is not
restriced, tokeep outthe leaves
Interesting – I’ve never seen a unit with a covered top because they want as much airflow as possible to efficiently transfer heat/cold from the coils. You can cover the unit when not in use, for example an air conditioner during the winter. Otherwise, if it has an open top, I wouldn’t do anything to affect the air flow (as you noted).
I’m actually dealing with this exact issue now with my mini-split outdoor units which have horizontal fans that tend to get covered with snow and leaves. I’m having a roof built above the units to protect them from debris without changing air flow.
My Trane unit has a covered top with side vents on the top instead. In my particular design i think it’s because it boosts efficiency in the winter not allowing snow and ice to get in and around the compressor/coil surface.
I have an early 50’s brick ranch and am looking for more ways to seal it and make it more efficient. It has about 8″ of blow in insulation in the attic. It has a decent amount vents on the eaves, a power vent on the roof and many other vents. The walls have had a hole cut and had blow in insulation stuffed in between every stud. It has new efficient windows through the entire house. The front door was replaced with a fiberglass one with a high R value. The storm door seals well. I installed a high efficiency heat pump, 97% furnace (dual fuel) for the backup heat being in Iowa and a new heat pump water heater (my old gas one was 25 years old anyway). The only issue I have is my floors are cold all around the edges of my house, especially when it’s really cold and i’m wondering if there is any remedy for that? Are there any other items you could recomend doing? I don’t tend to have any humidity issues in winter or summer. It can get a bit dry in the winter but not like my old leaky house. I’ve thought about radiant heat barrier but I kind of like being able to see the underside of my roof in case I want to spot any potential leaks or issues.
Matt,
Looks like you’ve done a lot of energy upgrades! Well done.
Regarding the cold floors around the edge of the house – I’ve seen that phenomenon before when the floor joists aren’t properly sealed where they meet the walls. This can allow a cold breeze to pass through the floor cavities from one side of the house to the other. Since the cold air warms up as it moves through the cavities by robbing the floors of heat, you get cold floors mostly near the edges, closest to the outside walls. A thermal scan with an infrared camera will clearly show this type of problem. You might also have the type of issue shown in this article. It’s the same idea.
If you did a thermal scan, you’d see exactly which spots were worst, allowing you to focus your remediation efforts. You could do it with a spot IR thermometer (for about $30) but it wouldn’t be as clear. The trick is fixing it. If it’s in the rooms with knee walls like the linked article, it’s easy. If it’s main floor and the floor abuts a normal outside wall, then it’s harder unless you have access in the basement below and you can inspect exactly what’s going on.
As for other things, the best way I’ve found is to simply walk room to room on a cold, windy day, and note the cold spots. This allows you to focus your efforts on the areas that actually cause problems. I would also turn off the heat pump when doing this test and feel each heating register (with no air blowing). This can reveal big problems, showing you where your ducts are leaking, allowing you go straight to the problem area. I’ve found some nasty issues this way. It doesn’t seem like your home suffers from bad ducts, but it can’t hurt to check.
The radiant barrier can make a big difference but with good attic floor insulation, I’d only go with a radiant barrier if you really wanted the attic space to be more comfortable. Like you said though, it would block visibility to the roof deck, so I probably wouldn’t bother.
Hope that gives you some ideas.
-Ted
Thanks for the insight. I’ve thought about checking it with thermal imaging. My issue is isolated to the floor only around the perimeter and my house is only one story. I do have a basement and the ceilings are not insulated which contributes to cold wood floors, but that is expected. My issue is just the very cold floors around the edges. These edges sit directly on the block foundation and I”ve just wondered if it’s just a bad connection between the initial wall beam and block that it sits on. I have access to most of the area in the basement. I have poked around but it just is hard to tell where it’s coming from. When you hold your hand up and feel around it, there really isn’t a breeze, it’s just radiating cold. That 2×6 that lays flat on top of the concrete block foundation is what my floor sits on where I have the cold spots so it may just be radiating from that. As the article said, wood is a poor insulator and well, concrete is worse. My basement walls are pretty darn cold in the winter.
On another subject, I read your article about the geospring water heater, which is what I purchased, and for anyone else looking, they have significantly improved their energy factor and made them more efficient in colder climates. They also fixed the issue that caused most of their problems initially, which was a cross threaded anode rod, leading to water leakage and leading to other issues. I also bought the ducting kit for it and have been trying to figure out a way to duct in warm garage air in the summer to boost the efficiency and provide fresh, cool, dry air for my basement. Routing the ducting is what has held me back from getting it done. I’ve done some measurements and you get about a 23-25 degree drop in temp from the input and output air however it could backfire on me because the unit will run the fan for quite a long time before and after the compressor has run to control the state of the refrigerant at shutoff and startup. This might cancel out any gains I got from using warm humid garage air initially. If i didn’t have a nice old brick house (that has too many holes already), i’d consider ducting it in and out in the summer.
Ted,
Great site – I just found it today. I have a 1960s ranch house (brick veneer) in western North Carolina (not in the mountains, in the foothills). Although we are not likely to be staying in this house, I would like to try and make it more comfortable. We just went through our first summer in this house and the air conditioner cycled on and off both day and night. I’m not sure about any insulation in the walls, but I do know that there is virtually no insulation in the attic. I believe that air sealing the attic and related prep work should be done first. I’ve done a lot of reading over the years at the Building Science site and it has great information, but in many cases the ideas presented are much easier to implement when you can start from scratch with new construction and apply a consistent approach to treating the home as an integrated system, say when insulating. It seems harder with an older home because when insulating one part of the house, such as an attic, it may not be practical or possible to insulate the whole house. I understand that insulating the attic alone needs to be done carefully in order to not create more problems than it solves. Our house has a fairly low-pitched roof, ridge vent and soffit vents I believe. The house is built on a crawl space that is quite dry for a mixed/humid location. AC/heat pump ductwork is in the crawl space. Your thoughts/suggestions would be greatly appreciated. Thanks.
I agree with everything you say, you’ve clearly been studying in the right places.
It is true that retrofits can be much more challenging than new construction. My roof is 4:12 and is a real pain to work in. I’ve spiked my head on roofing nails more than once so I now wear a hard-hat when I’m crawling around up there!
Since there’s little insulation up there, the task of looking for and sealing air leaks will be easier. Most weatherization people agree that the most practical method is to go after the easy fixes that make the biggest improvements and not sweat the small stuff which can take forever and yield minimal results.
Here’s some of the big things that come to mind:
Once you’re done sealing the big leaks, then insulate it as well as possible. You’ve done your research so I won’t belabor the details. But for others, here’s a couple options:
Hope that helps you get started. Cheers!
Ted,
Thanks for the quick reply. I’m not very familiar with the vent chutes. What size, what shape, made from what material? If I understand correctly, the vent chutes are parallel to the roof rafters, and as you said, their job is to keep from clogging the soffits with insulation. Technically speaking, the soffit vents are a series of vents running parallel to the gutter, eave, etc., but do we assume one soffit vent per EVERY pair of roof rafters? Just trying to figure out how many chutes are needed. Thanks again.
Here’s a link to one on Home Depot’s website. You’ll see exactly what they are in the photo on that page.
A good soffit vent will be a continuous opening along the length of the eaves so you would want the chutes/baffles between every pair of rafters. It’s a pain to install, especially with a low slope roof, but necessary to keep the air flowing unimpeded and reduce the risk of ice dams and moisture damage.
I have a vaulted ceiling in a 600sqft family room.We have had no problem in the 20 years of living here.However last year we noticed droplets on the ceiling but only in a small area.When I climbed up to the ceiling to wipe the moisture I noticed a small area of the wood ceiling was very warm.There is no electrical or water pipes anywhere near the problem.My homeowners insurance company sent a multitude of “experts” to find the answer and none of them could.So they threw $7500 at me to go away.Any ideas?
Here’s a bunch of follow-up questions that will help diagnose the issue:
What time of year did you see the moisture?
What was the outdoor temperature (approximately) when the moisture appears?
What time of day did you notice the warm spot on the ceiling?
Was it a sunny day?
Does the roof above the warm spot face the sun?
Is there staining on the ceiling at that area?
Were the droplets on the flat surfaces of the wood ceiling or at the joints? That is, did it look like the water is condensing on the ceiling or dripping from above?
Did you change anything else about the house between when things were “normal” and when you started seeing condensation. For example:
– Different heating system
– Added a humidifier
– New windows
– Other weather sealing
– Added lots of indoor plants?
– Added any other source of water inside the house, like a fountain etc.
– Any potential source of high moisture near that area of the family room?
We’ll figure this out!
We have a finished attic living space (steep roof). This is a “hot roof” no vents. The roof has older 1×4 ?? boards (not 4×8 sheets) under the shingles. I believe an ice dam barrier was put on when we put new shingles on ten years ago. We have never had ice problems. Fiberglass Insulation is directly under the roof not in the knee walls. There is an open spot in the peek of the roof where one would put gable vents but we do not have them.
We have recessed lighting and there is some condensation around the lights. Hot air gets trapped in the open peek.
Should we remove the recessed lighting and patch up the ceiling or replace them with led fixtures and seal them up tight?
Would gable vents help as I read that many older homes without soffit vents have gable vents.
This living area costs a lot to cool in the summer and heat in the winter (Minnesota climate). Any tips on keeping moisture out, venting and saving money on heating and cooling would be welcome!
Thanks, Beth
Converted attic spaces are often problematic for the reasons you mention. Unless they’re done really well, they are often plagued by hot summers, cold winters and moisture problems.
Based on your question about the possible gable vents, I’m guessing that part of the ceiling of the living space is flat, so that there’s a small attic above the living space where the gables are accessible? If so, then in your situation, having gable vents, one at each end, could help flush some of the hot air and moisture from that small attic space.
Now to the recessed lights. If you’re getting condensation around the lights, then I’m guessing the insulation was pulled back around the lights so that the fixtures are getting cold enough for condensation to occur. As you noted, the options are replacing the fixtures with LED recessed which are now available in very low profile, allowing you to insulate above them and seal them to the ceiling. Or, you could insulate and patch the ceiling and use a different lighting system.
Here’s a link to an example of low-profile LED lighting that might work. Note that I’m not endorsing this particular company or product, it just came up in a Google search. I haven’t used any of these so you’ll have to do some research to determine the best unit for your home.
I have a second home in Maine. I am looking at replacing my old oil furnace with an inverter-driven variable-flow heat pump system. I have no question about the ability of the heat pump system to provide the heat I need at low outdoor temperatures (with the use of supplemental electric heat at the lowest temps). However, since it is a second home, I am not there most of the time. When I am not there during the winter, I want to keep the thermostat setting down to the low 40’s – enough to keep the pipes from freezing but also minimizing as much as possible energy usage. I am finding systems that have great specs but which will not allow me to turn the thermostat down that low in the heating mode. Can you explain why the design of a heat pump system would not allow thermostat settings as low as I’m seeking? If this is beyond he capability of a heat pump system, then I’m going to have to forego the whole idea of a heat pump system in the first place. Setting the temp down to these low levels when I am not there is an absolute must.
That’s an interesting question. Maintaining temperature is simply a matter of providing enough heat to offset the heat loss, so maintaining a low temperature is physically possible using any system just by running it less. It sounds like more of a limit to the thermostat than a fundamental limit of the unit itself. You might see if they’d be willing to set up the system using a different thermostat that would allow you to reach the desired temperatures.
I will note however that it’s usually not recommended to turn it down that much for at least a couple of reasons.
First, the heating throughout the home isn’t uniform and some areas are likely to be in the 30’s, so freezing is still possible.
Related to that, if the pipes are inside any walls, the temperatures inside the walls may be much colder than the room temperature, freezing the pipes. I had exactly this situation in a property I own. The pipes went up through an interior wall, and the house was kept warm enough, but there was enough cold getting into the wall from the attic that the pipes froze solid during a cold snap. Keeping the house colder would almost guarantee frozen pipes somewhere.
Given the risk of water damage from frozen pipes (I’ve seen homes that had to be gutted after wintertime pipe freeze-ups) I would personally prefer to winterize a home – draining the pipes and turning off the supply, when away. If you can’t, then I’d keep the house at a higher temperature, maybe 55F.
We’ve hade good luck keeping the temp that low for several years now. I always shut the water supply and the water pump off in the basement anyway when we leave and the inside temp as gotten down to 40. Have had no burst pipes yet. I could always drain the water in the first and second floor pipes if I had to and put some antifreeze compound in the toilets. But there are a couple of water purification tanks in the basement that would be a real pain to winterize, and we are usually there for a few days each month to ski. Just not there most of the time. I have read today about some intelligent recovery heat pump thermostats. But I would need the lower temp setback to be able to be in effect for more than a week at a time. There is a nice Mitsubishi multizone system, but the minimum thermostat setting is 61F in heating mode. That is a non starter. I want to go down to at least 45F.
Glad it’s worked out for you. I try to be conservative in my advice since others may try to apply suggestions to their own homes, but you know what works for your place.
Depending on the specific heat pump you use, you may or may not be able to use an aftermarket thermostat. The mini-split heat pumps like the Mitsubishi tend to have proprietary thermostats so you’re stuck with what you have. Most central systems use standard wiring which would allow you to use a different thermostat with the controls you need. From your requirements, you’d need to make it clear to the contractor that you need the system to be able to be set down to 45F and write that into the contract so you don’t end up with nasty surprises.
Sorry I can’t provide more guidance, but it’s very system dependent so you’d be best off working with the HVAC companies to get what you need.
I am interested in using VB latex paint/primer or Foil under the underside of the metal.
Oh yeah. The metal shed has a Gable Style roof. If that means anything…
Ted oh my gosh I really really need your help man! Here’s the specs of the situation I’m facing: I have a metal shed that I am trying to convert into a tiny house it has 2×4 trusses. 24″ apart. The metal roof directly contacts the trusses. No decking or sheeting. Is air space required underneath the metal roof or can I have direct contact with a vapor barrier / radiant barrier and roll insulation underneath that . On the interior I plan on putting 4×8 sheets of double sided foil/foam board insulation. I would like to have a dead air space so that I do not have to mess with venting but I do not know if that is possible. The building is located in Missouri zone 5. I know that with 2x4s, there will be very little R rating but that is ok. Next year I plan on removing the roof and laying down some sort of decking to help with that. Can you please tell me what the air flow/material contact requirements are. Note: I am outside city limits with no rules to follow. Thanks Tedd. I hope to hear from you before my girlfriend loses faith in me! ;-).
Hmm, that’s a toughie. While you don’t have to worry about codes, you want to keep it safe. Shed’s usually aren’t built to the greatest standards of safety, so I personally wouldn’t live in it myself. That said, it’s your decision and I’ll try to answer your questions the best I can…
Regarding direct contact with the metal roof – metal is really prone to attracting condensation due to the heat conduction. It cools fast at night and heat hot in the day. Under normal circumstances, that daytime heat evaporates the condensation quickly. Doing anything that reduces that ability to eliminate water could create a real opportunity for a rotten roof. As such, the only insulation I would consider in direct contact with that surface is closed cell spray foam which would stop any moisture on the inside from coming in contact with the roof. It would essentially seal the bottom surface, pretty much eliminating the opportunity for rot unless there was a leak.
That said, you could also try foam board which would act as a vapor retarder. But in that case I would be very careful to leave a little air gap between the foam and the roof. I’d also seal the foam board against the support 2×4’s, caulking all gaps to minimize the chance of water vapor creeping into the gap. Even so, you’re likely to have some water vapor get in there, so I would still recommend allowing it to vent freely between the roof and foam board, allowing moisture to escape up and out at the ridge. Trapping moisture in there is a disaster waiting to happen.
You can certainly paint the underside of the metal to help reduce the risk of corrosion, but I’d still worry about it. That moisture can be a real bear to deal with in a completely trouble-free manner.
Hi Ted, just found your site after seemingly endless insulation research. I have very little insulation in an old 3-flat (3 apartments, 3 levels + attic) old brick building originally built around the 1900s and updated at various unknown times.
Currently there is no insulation under the roof rafters or the top ceiling/attic floor. There is significant ice damming in winter and I’m sure a bit too much heat is transferring through the ceiling and roof too quickly easily.
I would like to add insulation in an effective way to make the top floor apartment more comfortable in the winter and more efficient without creating mold and moisture problems. After reading a lot of articles on Building Science Corporation and GBI, it can seem like everything is either risky or asking for trouble, or so expensive that it wouldn’t be worth doing.
The walls are structural brick walls (exposed brick on interior except in parts where drywall and studs with no insulation) and there is a gable wall at each end of the building. The back brick wall is actually no longer the exterior, as there is a framed in enclosed porch and stairway off the back of the building.
The forced air furnace and ductwork for the top floor apartment unit is located in the attic. So are the water heaters. It would be way too complicated and labor intensive and sacrifice too much space to move any of these things. Also my family wants to be able to use part of the attic as usable livable space.
My original plan after getting a bunch of quotes for cellulose and spray foam options, was to have an insulation company spray-in dense packed cellulose, making the roof deck or attic interior basically an insulated unvented cathedral ceiling. The insulation company also proposed installing a perforated radiant barrier (R+HEATSHIELD Perforated: Aluminum Foil/LDPE Scrim/Aluminum Foil) below the cellulose insulated roof deck/ at the attic ceiling. And adding cellulose insulation into the attic floor to slow heat transfer from the top floor apartment to the attic. The rafters are 2x6s, which means the R-value of the roof would not be as much R-value as recommend for the region. I’m in Region 5, but not too far away from Region 6. All the cellulose would be installed at close to the usual 3.5 lb/ft3 [56 kg/m3] density.
I later learned that “air/moisture permeable” insulation is not recommended without also adding the recommending R-value of exterior foam board insulation too. The roof is a recent ~3 year old tear off, shingles over new plywood roof, so it would be hard to justify tearing off the roof just to add exterior insulation.
I also later learned that I actually have a ridge vent, which led to more research. The building has no eaves or soffits, the gutters are very close to the walls. So the ridge vent is probably not doing anything good, and possibly should be sealed. Alternatively, the insulation company offered the alternative of adding baffles below the insulation, just under the roof deck. This would reduce the insulation thickness and R-value, and I’m not sure if it would be safer or less safe from a moisture issue perspective.
If keeping the roof ventilated “correctly” I would need to add shingle vents, which adds another unwanted cost. I’m not sure if the ridge vent would still work by allowing moisture to diffuse out without lower level inlets and no other venting.
So I’m wondering if it is still a good idea (and not as risky as some would say) to add cellulose as planned, and whether to go vented, leave ridge vent as-is with no new vents and add baffles, or unvented with no baffles and seal the ridge vent. I don’t think I want to add new under shingle vents, but that is another option.
Plan B is probably to do nothing and just use more gas everything winter, as doing everything 100% to code will close cell foam , or tearing off the roof again, (I looked at IRC 806.5 and the Building Science articles) looks more expensive than remaining extremely inefficient and using more natural gas.
You’re doing your homework and your assessments sound on-target. That vintage is always tough. As you noted, the ice damming is certainly a sign of excess heat loss in the winter. It’s likely the lack of insulation but could also be made worse if there’s heat loss up through the wall cavities that’s heating the underside of the roof. A careful visual inspection could help you track that down. You always want to deal with air flow issues if they exist before adding insulation.
In that vintage, I’ve seen the cavities behind brick walls that run straight up from the basement to the attic so all that warm air has a clear path right up the inside of the walls. The problem is, you can create unintended consequences by “fixing” this air flow. For example, this air flow, if it exists, would dry out the interior of the wall behind the brick. If stopped, moisture could build up. This is just an example since you didn’t mention anything like this, but I mention it just to bring up some of the more subtle side-effects that can arise.
To your specific question about cellulose in the attic – I’d be hesitant to do the double layer (under the roof and on the attic floor) because that could create a cold dead-air space that could be prone to moisture buildup. You want one or the other, not both.
You mentioned that you want to keep the attic potentially livable. If that’s the case, then, IMHO, the logical choice would be to take the unvented cathedral ceiling approach and allow the attic space to be conditioned with the HVAC, keeping air flowing through the space to flush out moisture and eventually to keep it at living temperature. You could do cellulose with an air barrier under it, but it can’t be less than 100%. For example, just stapling up radiant barrier under it wouldn’t help eliminate moisture migration up through the cellulose and onto your new roof. I’d be really worried about inducing a rot problem that way. The most sure-fire approach would be close-cell spray foam encapsulating the attic, sprayed from the inside up to the underside of the roof deck. While the $/sf cost is high, when you start adding up the material and labor costs of doing it other ways, you may find that the other approaches are even more expenses if they’re done right. If not done right, you run the risk of a rotten roof in a few years.
This approach of course makes the question of the ridge vent moot as it would be sealed up from the inside by the foam, so you would just ignore that.
Cheers!
Ted thank you so much, for your first reply. I cancelled plans to use cellulose shortly after, but have since been stuck for months on deciding on the best approach considering costs, risks, and benefits.
I’ve been reluctantly settling towards the conclusion that the only good solution for my non-insulated attic with poorly sealed and poorly insulated ductwork and a new roof is to install closed cell foam and possibly foam board below it and finish with drywall get some more usable living space. I would have professionals spray closed cell foam working from inside the attic to apply under the roof deck to 4.25 inches to 6 inches of thickness, between the rafters and after or partly before and complete after, attach a double layer (with edges/seams offset) foil faced poly iso boards below the rafters. The rafters are 6 inches deep, but there would be various areas that prevent the full depth of the space between all rafters from being entirely filled with closed cell foam, due to the wood being in the space. The main downsides to this approach that I realized so far are the expense of closed cell foam and that adding poly iso board will make the not that spacious, but still large and tall enough to be comfortable to walk in attic a bit smaller.
I’m not sure if 2″, 3/4″, or 1.5″ for the poly iso board thickness makes sense.
An issue I’m stuck on is: How good/bad is it to insulate below current code, but way more R-value than currently and stop there? Will I be better off with only approximately R24 and closed cell foam in an area where code calls for R49, compared to the R value of plywood and asphalt shingles by themselves? Or would it be worth the trouble and cost to at around the same time, add an additonal R18.5 or R26 and lose 3 or 4 inches of space by adding a double layer of thicker poly iso boards, which I think should also greatly reduce the effect of thermal bridging through the rafter wood. Using closed cell foam alone will only get an R value of R42 at best to as low as R24, (assuming R7 or R6 per inch of thickness, and 4-6 inches of thickness) and by itself would still allow thermal bridging at the rafters.
I am still also considering insulating the attic floor to slow down heat transfer from the apartment below, such that the attic might hopefully stay around the same temperature as the apartment, instead of far warmer than the apartment,… given that the ductwork is running partially open in the attic with R-4 marked duct insulation above the attic floor and can lights in the ceiling below are leaky enough to heat the attic space below the cathedral ceiling/roof deck of the attic.I’m second guessing whether this is fallacy (am I not thinking enough like a ‘child that listens’), but my thought was that due to furnace and ductwork leaks and inefficiency should be enough to keep the attic as conditioned as the main apartment, even if the floor/ceiling is well air sealed and somewhat insulated – in reality the floor/ceiling is still very leaky, but air flow might be reduced by better sealing in obvious areas at some point. I was considering DIY attic floor/apartment ceiling insulation with mineral/rockwool batts, not intended to perfectly insulate, just to slow down transfer of heat into the attic and reduce sound transmission. There are a lot of light cans and junction boxes, as well as gaps around the edges of the walls which might be somewhat better sealed at some point.
Also, any thoughts on these:
“cut and cobble” http://www.greenbuildingadvisor.com/blogs/dept/musings/cut-and-cobble-insulation
Adding natural light via skylights or light tubes, I was reading BSI-063: Overroofing by Joseph Lsitburek at Building Science. Once the attic becomes insulated it would be nice to have natural light in the added livable space, but obviously skylights or light tubes would create relatively poorly insulated spots.
Regarding other background info: Enough brick is visible (fully exposed from interior) that i am fairly sure it is solid brick (no spaces running vertically) with some wood pieces on the interior long since removed by previous owners plaster/lathe. The lower level walls are thicker (more layers of same type/age brick) than the upper level, and the transition i thickness between floors can be observed in a few locations. The brick walls are exposed on both the interior and exterior walls, except walls in bedrooms and baths, kitchens where there is modern drywall over studs and no insulation. I read the article BSI-047: Thick as a Brick, and concluded it is best to leave the brick walls uninsulated to prevent freeze thaw damage, by allowing the building to continue to warm the walls, for this reason I was planning to also leave the brick gable walls in the attic uninsulated – better to lose heat/efficiency than potentially risk of having the walls disintegrate.
Basically I feel any efficiency/insulation improvements other than the attic will need to be limited reducing leaks around windows and doors.
Last winter the apartment may have been kept around 55-60 F, but the attic would be around 75-80 F and the roof deck would even be warm to the tough if i recall correctly. I just realized i have old infrared photos to reference and on a day in December between 28-31 F outside temperature, roof deck and joists were 60-70F, Temperatures on Furnace and ductwork were visible, mostly in 70-90 F range, but as high as 130 F in a few spots on furnace.
The radiant barrier proposed by the cellulose company, was perforated to avoid creating a vapor barrier as the insulation company did say that the cellulose should be installed without a vapor barrier.
Wow, that’s a detailed question. Looks like something I might write 🙂
Let’s take this question by question.
Regarding R-value below code
Two answers – first, you need to talk to your local building official to ensure you won’t get dinged at some later time, such as when you sell your house. That would be really painful. When in doubt, go by the book.
Switching hats…You, I, and every building scientist knows that foaming then adding iso-board to reduce thermal bridging will result in a much better insulated and tighter home than would blowing in code level insulation. It’s well known that thermal bridging dramatically reduces the effective R-value of normal cavity-only insulation. If I had my spreadsheet handy, I’d run the numbers for you, but I think you can look it up or figure it out.
But code enforcement officers look at their little chart, pull out their ruler, and say “nope, code says R-49, yours is substandard.” So just make sure whatever you do is allowable for your jurisdiction.
Regarding insulating the attic floor
Am I reading this correctly that you want to insulate the attic floor (for a variety of reasons) in addition to the attic ceiling/underside of the roof? Or are you saying floor instead of roof?
If the former, then it would very well be that the heat loss from the ducts and from the house/cans/etc. is enough to heat the space. But you just won’t know until you try it. You could run heat-loss/gain calculations and try to compute the heating requirements for the space and see if the numbers make sense. If I were in your shoes, I’d probably insulate the roof like you suggest and see what it’s like in there. But I also wouldn’t count on unintentional heat loss for heating the space. I’d rather seal everything up proper, then intentionally heat/cool the attic space, probably using a mini-split heat pump, so it has it’s own dedicated zone and doesn’t adversely effect the rest of your home’s heating/cooling.
Regarding cut-and-cobble
If you’ve got time, why not? DIY solutions like this can certainly work well if you do them since you’re in control of your own QC. I wouldn’t trust anybody else to do it since they’re bound to take short cuts and take a lot of time so the ultimate cost would be less if you just had everything spray foamed.
Light tubes
I love light tubes in normal living spaces. I installed a few in my home and have recommended them to others. In an attic ceiling, it could be tough because you’ve got a small working distance. But it’s probably possible. As for energy loss, you’re right, you’re creating a low-R hole in your ceiling. I wouldn’t install skylights which are 5-10 sq. ft of low-R. A sun tube is going to be about 1 sq. ft., so the loss/gain would be much less.
Brick gable walls
Well, if you’re going to leave that uninsulated, that’s orders of magnitude more heat loss than sun tubes vs. skylights vs. being a few points below code R-value. I just read BSI-047 and it is a bit scary. You have to do what you think is best!
We live in Florida, Cocoa Beach/Merritt Island area. Do you have a name of someone who is an independent energy consultant to diagnose our problem? Thank you!
I’m not really familiar with the contractors in that area. You might contact your local building code enforcement officer. They often have a line on the professionals in the area.
Hi Ted,
Your article on sealing a loose attic duct boot from ceiling side was helpful
http://www.etccreations.com/retrofit/sealing-ducts
If weatherstripping is used to seal the gaps near boot, do the screws go through ceiling then just into the weather strip at four corners? Since the boot is not attached now, I dont see how I could screw through metal boot. Also, my ceilings are plaster, so any related tips for securing the boot after sealing gaps?
Thank you,
Peter
I’ve got a fair amount of plaster in my home as well. It’s definitely a challenge since it’s so hard and flakes/cracks.
You could try pre-drilling with a relatively small drill, maybe 1/8″. I think that would go through the plaster without too much damage if you’re careful to keep the bit straight as you drill. Any sideways pressure and you’re going to risk cracking the plaster.
Usually you can reach into the sheet metal boot and get a grip enough to drill through like this. I’d do four screws – one centered on each edge of the boot. Then, when tightening, tighten just enough to compress the weatherstrip. This helps reduce the risk of cracking the plaster.
A final suggestion – get a roll of “foil mastic” tape. This has an amazing adhesive that is really strong. Clean the inside of the boot where you’ll tape it, so that it’s free of oils and dust – plain baby wipes work great for this. Dry it thoroughly with paper towel. Then run strips of tape along each edge of the boot, leaving enough to bring the tape around and onto your ceiling for about 1/2″ – 3/4″. Trim the tape so it doesn’t show around the grill/register. If you do this, you can get by with 2 screws because the tape holds so securely. You can even tape the boot first, then add the screws for extra security. I’ve even skipped the screws because the tape holds so well. In your case with the plaster ceiling, you might try this.
Note – make sure to get the right tape. The cheap foil tape sold at big-box stores doesn’t have the rubber adhesive strip and won’t stick well to the plaster. The Foil Mastic tape will hold for the lifetime of your home.
Wow, quick and thorough reply, thank you again,
Peter
Ted,
I live in the mountains of Colorado, 80s in the summer and -30 from time to time in the winter. Fairly low humidity most of the time here at 7400 feet. I’ve got a 40 year old house with R37 Fiberglass in half the attic and R14 in the 8×32 foot walk space used for storage. The R14 fiberglass is under 2×8 boards. My rafters are 6 inches so I can’t really pack more under the 2x8s. It has been suggested that I just stack 4 inches of interlocking blueboard on top of my 2x8s and then put particle board over top of that to form a new attic floor for storage. I’ve already torn up the 2x8s once and used Greatstuff on every crack and gap I found, as well as latex caulk on the inside wherever I found cracks on the drywall seams. Am I in danger of moisture issues? If I can put the blueboard in, can I glue it together with Greatstuff?
Andrew,
The moisture would be coming from the interior of the house, so if you put blueboard above the insulation/floor boards, there is a chance that you’d trap moisture as you suggest. It all depends upon the temperature of the bottom of the blueboard (that faces the existing insulation). Basically, you want to let any water vapor that gets to the top of the existing insulation/floorboards to escape and flush out of the attic. I also would not use particle board as flooring since that can deteriorate over time and become hazardous. Over blueboard it would be ok since that provides a stable surface, but since I’m suggesting a different approach, I’d do something different than the particle board also.
I’m actually in a similar situation with my house, with a long central walkway over small rafters. But I don’t store stuff up there, so I just laid thick batts over the floorboards in the less used areas and allowed the compromise of low insulation in the small section between my access and the air handler which is up there.
Since you want to use it for storage, how about setting up 2×8’s perpendicular to the existing rafters, with some cross braces (picture a ladder built of 2×8’s) then adding unfaced batt insulation, or loose fill, inside the new boxed out area. Then you could make a floor on top of that, using loosely fitting 1×8’s or whatever. This would allow water vapor to escape between the cracks, minimizing the chance of moisture issues.
hey ted had a question about my water heater that has been diagnosed as stage four /terminal. i am looking at a sears electric installed 55 gallon with 12 year warranty including expansion tank and protection plus for about 1350.00 . my oil company quoted me for a 50 gallon jp hwp 1640. upon questioning the difference, my old 18 year old water heatwr was connected to my oil burner and is a very different animal as per the heating company rep. so do i stick with the oil fired unit for about 300 more or move to electric to early savings. will that be a regrettable move? thanks bruce (you were very helpful with my heating dillemna last year with my summer cottage , so i am taking a shot before i purchase)
Hmm, I replied to your water heater a while back but don’t see my reply in the discussion thread. Let me know if you got my comments.
2nd story addition, non-vented cathedral ceiling question.
Southern California ~ 15 miles from coast. Summer highs ~100, Winter lows ~ 25 (at the extremes)
The cathedral ceiling is a double stack – exposed beams, 2×6” T&G, 2×10 rafters, roof sheathing, asphalt shingle. High fire zone so attic vents are not permitted. Lots of can lights and fire sprinklers penetrating the T&G. The roof sheathing has not yet been installed, ready for insulation then we will sheath and roof.
Plan A was to smoosh R-30 bats into the rafter space (measures 11” tall) but after a bit of research I’ve become quite concerned about condensation. Is condensation even an issue in Southern California roofs? Plenty of ways for moist air to enter the insulation void from the house, but no venting for it to escape or “draw”.
Plan B is to spray in 11“ of open cell foam. An expensive option (4K vs 1K) and open cell foam isn’t a vapor barrier.
Plan C has me even more confused – Flash and Bat. I can spray 1-2” of closed cell on the top of the T&G, providing a good vapor barrier and sealing all the can light and fire sprinkler “leaks” then place R-19 and sheath the roof. But, I thought flash and bat was intended for the “flash” to be directly on the underside of the roof sheathing. An article I read of yours stated the opposite? Also getting really $$ now…
Hopefully you can point me in the correct direction. Running out of money at this stage of the project and don’t want to throw $$ at a non-problem. But definitely don’t want to create a “sick” roof.
Thank you!
Matt
Good questions Matt. Typically I’m not a fan of flash-and-batt but it does depend on the location of the vapor drive. In the case you’re describing, the worst vapor problems are most likely going to come from the house, so you would want to use the thin layer of foam as you described – directly against the T&G, giving you an air and moisture barrier. Then the batts between that and the roof sheathing. I’d leave a little gap between the batts and the roof since most of the moisture problems occur when the batts act like a sponge and hold the moisture against the roof sheathing.
The biggest concern with T&G ceilings is the house air/moisture moving through them and into that roof cavity so I’d definitely go with a foam solution.
Thank you Ted! I hadn’t budget foam for insulation but you definitely confirmed my belief that it is money well spent. I’m having 11″ of open cell sprayed this Tuesday, filling the rafter bays.
Have a great weekend!
Matt
Hi Ted,
instead of flimsy vents chutes in my attic that will not be finished, would it be ok to use wood or thin foam board attached perpendicular to the roof rafters and then foamed to another piece of foam on the ceiling plates??? Very low roof lines in my 1.5 story home and difficult to try and seal around a chute to stop wind washing.
thank you
Ted! Thanks for your comprehensive review on heat pump learned so much and frankly your article summed it up very nicely for me to make this decision simpler.
I’ve pulled the trigger on 2 – 25VN024A (3T) and 2 – 59MN7A (60K 2nd fl and 80K 1st fl btus) as backup heat propane. Based of Man J it’s requiring total net ton required is 1st Fl 2.38T NetGain 28,580 SenLoss 52,700 – 2650Sf 10ft ceiling and 2nd 2.01Ton NetGain 24,125 SenLoss 44,250 2375sf. Contractor recommended 3Ton for each fl. I have plans on finishing the basement in the future (1200-1600sf more) so may require more heat and therefore bumped up to 80K for the backup – why not same for HP not sure – hence this post.
Based on what I read, I’m sold on increasing the 1st fl to 4T but my contractor seems against it because it will require 400cfm addition of return air which he thinks is hard to do. My thought is that if I have 4T HP it would work more efficiently in those low temp (am in PA bucks county New Hope, PA) and it wouldn’t have need to tap into backup as propane is much more expensive. Also for cooling side it’s my understanding that it can operate at lower cooling capacity eg set unit to run at 50% capacity at cooling so it’s not a huge concern. For cooling i can understand as basement will not require increase in capacity. 400cfm can come from basement if required so am not understanding his rational of not bumping it up. It’s a new construction and price difference is very small for going with 4T HP on 1st fl as well as return ducts can be added if req.
Your thoughts and suggestions would be greatly appreciated on weather to bump it up or not.
So happy to help. I hope it works like a charm!
You’re in New Hope? Me too! Small world indeed.
I tried looking up those model numbers but nothing’s coming up on Google. Can you give me the generic product names. I’m trying to double check some specs. because something doesn’t add up. You said the 25VN024A is 3T. By most standard conventions, the 024 identifies it as a 24kBTU = 2 tons.
Also, what temperatures are they using as reference for the loss/gain calculations? Usually it’s standardized but I try not to assume too much.
Typically, in our area, I like to look at the output curves for the units and compare that to the demand curves for the house. Depending on the technology (single stage, two-stage, inverter drive), I recommend more or less conservative approaches. With a central system and a two-stage compressor, you usually don’t get 50% output on “low”. It’s actually significantly higher. This can be problematic if you upsize the unit because so much of our summer heat is high humidity, moderate temperature – where you want to run “low and slow”. I wouldn’t want you to end up in a situation where the humidity remains oppressive just so you can squeeze out a bit more efficiency during the winter.
To your point – I don’t really know why he thinks the additional 400cfm would be difficult in a new construction. A lot of people are hung up on returns, but honestly, You don’t often find a home that is so tight that the returns make a big difference. Remember the old days – central systems only had one huge return in the hall below the air handler (like in my house). You just left a little room under the doors for the air to flow and everything was fine. In a new construction, it’s even less of a concern. Maybe they run an extra couple of ducts through the walls, say to the master suite, great room and kitchen.
Hope that helps. If you have more information on the units, shoot it over and I’ll see if I can dig up some tech info.
Small World Indeed 🙂
So it’s the Infinity greenspeed 25VNA0 3T Variable Speed – have a query out to him for exact model# details. Daily temp says Medium on load J – See below may i’m not reading correctly. I thought that greenspeed can adjust to run at low capacity so humidity issue would be taken care of from an oversize perspective.
Daily Temperature Range: Medium
OD=Out Door/ ID = Indoor
OD DryBulb OD WetBulb OD Rel.Hum ID Rel.Hum ID DryBulb Grain Difference
Winter: 14 12.83 n/a n/a 70 n/a
Summer: 88 74 52% 50% 75 39
59MN7A080-17-14-Heater 1st fl backup
59MN7A060-17-14-Heater 2nd fl
CNPVP4217ALA-Coils
25VNA036A003-HPumps s
SYSTXCCITC01A-Stats
Aprilaire Model 700M
Oh, I am so jealous. Those Greenspeed systems are amazing.
Here’s the tech manual if you’re interested
Click to access 00022.PDF
The 3-ton units have great performance curves at various temperatures. See page 11. You’ve still got over 30,000 BTUs/h at 20F so your propane shouldn’t have to turn on until quite a low temperature. Make sure that they show you how to program the thermostat switch-over point because that will make all the difference. And, while the calculations will get you close, nothing like living with the system will tell you exactly where you want the propane to turn on. It might be 15F. It might be 30F.
If you do go with the 4-ton unit, that gives a full 4-ton output at 20F and still over 3-tons at 10F so you’d probably never need to use the propane in our climate. That would be pretty tempting. However, as I suspected, even the low speed cooling output would probably be too high. The 4-ton unit puts out 34,800 BTU/h of cooling at low speed, which would not be good for dehumidification in our climate.
Based on these things, I would stick with the 3-ton. You’ll be substantially more comfortable in the summer. Yes, you’ll have to use some propane in the winter, but overall, the compromises between operational cost and comfort would lead me to prioritize comfort higher. In the long run, I think you’ll be happier.
Perfect, will go with 3T based on your take. It’s 1/2T more than required so should be fine. Was very tempted to oversize – to gain more heating efficiency & very small price difference upfront.
Thank you for your prompt response and honest opinion. Email me – I would be glad to take you out for a beer or two as you’re in the area. Otherwise will donate!
Ted,
It would have been nice if I would have seen you blog BEFORE I replaced my roof. Can you address proper roof ventilation for steep pitch roofs, 12/12 or steeper? Should an owner in your opinion, use ridge vent with edge vent? Or is edge vent simply another form of air chutes, i.e. a band aide for fixing the air circulation problem. Gable vents are not an option due to the design of the roof, and a chimney in the middle of the ridge line.
Just heading out the door so I’ll give you a quick answer. A proper venting system needs an air inlet and an air outlet. Therefore you need vents at the soffits and the ridge vent. The air will travel into the soffits up the underside of the roof and out the ridge vent.
I highly recommend reviewing the literature on cor – a – vent. their website has excellent information showing exactly how this should work. and, their product, is superior to the cheaper ones on the market.
If I think of more I’ll add to the comments later. Good luck.
Hi Ted,
I was looking through your site and came across your articles on air filters. Thanks for such informative content! I also wanted to let you know about a related resource that you and your readers might be interested in (we’ll let you be the judge of course).
It’s all about MERV Ratings: https://airfilterbuy.com/all-about-merv-ratings
You’re more than welcome to include it on your site if you think your readers would find it valuable and helpful. We might be open to paying a fee if the price makes sense.
Thanks!
Jeff Oxford
(760) 522-2097
Jeff.AirFilterBuy@gmail.com
Air Filter Buy
Hi Ted,
I wrote twice before. Your comments were very helpful! The first time was to ask whether it would be contra-indicated to have blown-in cellulose put into my vaulted ceiling in my 1969 raised ranch home. You said, go for it, as long as they do it right and snake a hose down into the cavity, and etc. They did not, and I wrote again asking how much of a problem this might pose. You said basically I’d probably be OK, particularly as paint can help form a vapor retardant barrier, and I have painted sheetrock ceilings. In that I am about to have my ceilings repainted, I spoke to Benjamin Moore, and they said their latex paints are probably not much of a vapor barrier, but that I could use a vapor-proof primer they make.
My current question: should I do this? On the one hand, this sounds great. I could prevent further migration of vapor into the cavities in the winter and thus reduce the chances of condensation. On the other hand, I have this fear that if I do it over the summer, I am somehow sealing in whatever vapor is in there now (which could be a lot as we enter the humid months) and that it would then be “stuck” in there as colder months come upon us.
What do you think? Is the latter a legitimate concern or will the humidity slowly dissipate from the cavities as the air becomes cooler and less humid, and thus it would then mainly be protective against new vapor travelling in during winter as hot air rises upward from my heated home?
Thanks!
Nate
Latex paint is a class 3 vapor retarder but keep in mind that each coat adds to the retardance, so a couple coats is pretty good. It’s not like adding plastic to the cavity but unless you’re in an extreme climate, that’s not necessary.
As for trapped moisture, that’s not likely a concern. The amount of moisture that goes through the sealed drywall is very low to start with. The cellulose has the ability to distribute the moisture allowing the cavity to hold more moisture before doing damage. This allows the cavity to dry over a period. Having a moderate perm rating lets the moisture slowly get out. All in all, the risk is low unless conditions are extremely wet.
There have been a lot of interesting comments about the Fujitsu mini-splits but what about other brands such as Mitsubishi? We’re remodeling what has been a three season cabin in the upper Midwest and converting it to four season so we’re leaning toward the Mitsubishi min-spit as the best option since most of our time there will be during the summer months anyway. I’m planning to use spray foam to insulate (again, mostly to keep the cool air in) and hopefully condition the air so it’s not so humid.
Also, It’s been suggested that we use radian cove heating panels for the winter months to supplement if using it then. Do you have any thoughts about this option as well? Thanks.
Mike
Generally speaking, the Mitsubishi units are considered the workhorses of the industry. Almost every installer I know that isn’t looking for the cheapest unit on the market, uses Mitsubishi because they’re reliable and appear to last for many years.
Like all products, you will find some horror stories, but generally, I’ve heard only good about them.
As with any HVAC system, the real key is going to be getting a great installer who has years of experience installing systems and will go to bat for you if there is any problem.
I do recommend some form of backup heating for winter use. Especially if you’re in a climate that frequently gets down below 20 degrees Fahrenheit. while these mini splits do an admirable job, physics dictates that their output will drop so having a cheap electric panel / radiator is a good idea. plus, if you get a heavy snows, those can prove problematic. I had to turn one of my units off for most of the winter because it clogged with ice from the big snows we had. I was very glad we had backup heating sources at that point!
An additional note – you asked specifically about Radiant Cove heating panels – I’m a little dubious about mounting convection heaters on the ceiling. As it is, I tend to see quite a big difference between floor and ceiling temperatures using baseboard heaters, and I can’t imagine ceiling mount would be better. In addition, you’re paying more money from a product from a single source, whereas you can get standard electric baseboard heaters from many companies, in different sizes and power levels.
Thank you for the responses. I’m glad I read about the issues with the Fujitsu as that was the other option my installer offered but as with most things, the life cycle costs often include a larger investment for quality up front. I also appreciate the information on insulating a ceiling with a pitch on it. This cabin we’re remodeling to four season has only a 5 to 1 slope on the roof. It’s 20 ft wide by 27 ft long so to save some money, I was going to spray foam about 2.5 inches in the ceiling and put batting in the rest of the space. I hadn’t thought of the moisture issue that could arise. I’m not sure if the denim or wool batting is any different, but it seems that paying the extra money for the spray foam is the best route.
Regarding the cove heaters, for a 540 sq ft structure which includes two bedrooms, kitchen and small living room, this seemed like a good option due to limitations of space and walls. Radiant floor heating isn’t a very good option (I think), though doable, since the slab floor is already existing and it would mean taking out a sizable area unless we went on top. I’m not sure how thin the electric floor heat could be. Although it’d feel the best. Are there any other electric options we could consider? There is an existing 35K BTU LP free standing furnace (Empire) but it takes floor space and does not have a thermostat but only a fan speed from 1 to 7. At 45 degrees latitude, we get our share of below zero nights (25 on average to be exact) so backup heat would be essential. Thanks!
Actually, I was thinking of just plain electric baseboards, but with space considerations, maybe the cove heaters would do the trick. Hopefully, someone else has had some experience with these and can give an opinion.
It’s a pretty small space, and if you’re doing good insulation and a tight structure, there will be less to worry about, though it depends on how high your ceilings are. My main room has pretty high ceilings so the heat tends to pool at the ceiling. Turning on the ceiling fan raises the room temperature 3-4 degrees but the draft is annoying. If you’ve got a normal 8′ ceiling, the stratification problems would be much less.
Be really careful with the spray foam since a tight house is much more prone to moisture problems. Dead air spaces, in particular, are prone to moisture build-up. By dead air space, I mean like an unvented attic space that has had the ceiling (underside of the roof) sprayed. You also want to ensure that any bathrooms with showers are very well vented with fans strong enough to flush out the moisture. I just was on a troubleshooting job where bathroom venting appears to be too weak and the moisture buildup was so bad it was raining in the house as the water dripped off the foam.