Ask Ted!

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!


744 thoughts on “Ask Ted!

  1. Craig, it is always suspicious when homes that formerly had no problems suddenly develop issues. From your description, it sounds like there’s moisture buildup that’s causing the paint to come off and the potential mold growth.
    Typically, adding insulation wouldn’t cause a problem like this because it would help to warm the ceiling which would reduce the chance of moisture buildup. On the other hand, it’s possible that the lack of insulation allowed the ceiling to stay warmer when the sun was out because more of the attic’s heat would radiate downward, heating the ceiling and causing moisture to evaporate more quickly.
    Do you remember when the paint and black dots started appearing? Was it this winter?
    Another question – do you have any moisture sources in your bedroom, like using a humidifier or plants? Or is the problem area near the bathroom where moisture from the shower could be coming into the bedroom?
    The key is to reduce interior moisture and be diligent in flushing out moisture that may accumulate. I always advise people NOT to use humidifiers and to run bathroom vent fans for 20-30 minutes after taking a shower to flush out all the humidity. Also, verify that the bath fan is working by placing a sheet of paper up the the fan grille and seeing if it sucks onto the grill tightly, indicating good air flow.
    If you don’t have a mold sensitivity, you should clean off the black dots from the ceiling using a soap-water solution. Many people will say bleach, but that’s dangerous to inhale and simple soap-water will dissolve mold and wash it right away. Be sure to thoroughly dry the area and monitor it over time to ensure it doesn’t come back.

    • Hi Ted,

      Thanks for the quick response. This started shortly after the insulation went in and it was before winter. I don’t know what else to do. I had a painter friend come out and look at it. He said the paint is old and he would scrape and redo it for me.

      I should mention that it is right above my sliding glass door. I would like to send you some pictures if possible to show you. The humidity does get kind of high in the house so I don’t know if that has something to do with it. Other than tearing out the insulation, I don’t know what else to do.

      • It’s possibly coincidental.
        I wouldn’t do anything drastic like pulling the insulation before doing more observations over time.
        If you friend can scrape and repaint, that will give you an opportunity to see how it progresses over time. In particular, I would look for any signs of condensation at that location.
        You should also consider using a dehumidifier in the room. High humidity is rarely good for homes so if the humidity is noticeably high, dehumidification is called for. You want to keep the humidity between 40%-60%. Above 60% and you have ripe conditions for mold.

  2. Hi Ted,

    I live in San Francisco in a home that was built in 1928 with no insulation. I had the flat roof replaced about a year ago. During that time, I asked the roofer if he could install insulation which he did. There isn’t a lot of room between the ceiling and my roof, but he was able to put rolled in pink insulation R-30 I believe. Now, I am starting to see some black dots along the edge of my bedroom ceiling and the paint is starting to crack and peel where it wasn’t a problem before. I have asked the roofer and contractors and they said it is not from the insulation. They did say to control the humidity which is probably causing the issue. This wasn’t a problem before, but now I’m wondering maybe that’s why these older homes never had insulation so they could breathe.

  3. Hi Ted.

    I have an 1840’s farmhouse in NY that I’ve been working on for the past few years. I’m doing sort of a restore yet modernizing where possible. This year I plan on residing the house. I’ll be using all sides primed western red cedar to match the existing. If the South and West sides weren’t to the point of no return I would be scraping and painting. Anyway, I figured why not insulate the exterior walls while I’m at it and my main question is what to use. The house is timber frame with the studs mortised into the sills/beams, etc. and they are full dimension 2×4’s. There is no sheathing and I’m not going to add any, nor any insulation board as I’m not padding out the window trim, etc. Those have been getting restored and I’m getting pretty good at glazing sashes! My initial thought is to use Roxul batts and then a house wrap, forgoing any vapor retarder completely and letting any cavity moisture dry to the exterior through the wrap and siding since the wood will be sealed on the interior side. At the same time making sure to air seal any gaps, cracks or holes on the interior envelope with canned spray foam to slow down the vapor intrusion. First off, is this a good idea? I restored the plaster walls on the interior so installing a vapor retarder on the interior was never an option.

    The other question would be that if this is a good idea, would the 1/2″ gap between the siding and insulation have a negative effect due to convection? And if this is not a good idea, I’d be grateful for a suggestion! I’ve been trying to really research all of this but cannot seem to find a real answer! Thanks!

    • To make sure I’m understanding what you’re describing – you’re removing and rehabbing the siding. While the siding is off, you’d like to insulate the walls, which are plaster inside. You don’t want to add exterior insulation as that will increase the thickness of the walls, necessitating extending the window jambs.

      My first choice in your situation would be to foam in the walls with closed cell foam, spraying right to the back of the plaster interior and filling in the cavities. That would air seal and the walls, insulate them well and be water resistant.

      You mention using batt insulation, like Roxul, with a layer of house wrap over that. You could certainly do that. The house wrap will be vapor permeable and will shed water that might get in behind the siding. If well taped at the seams, it would also do a pretty good job of minimizing the wind-wash that would compromise the insulation.

      A small gap between the insulation and siding would be recommended to avoid water getting trapped between the insulation and siding which could rot it. If you use the house wrap across the studs, that will lock the Roxul in the cavities, then you’d use nailers to ensure a gap remains between the siding and the house wrap. You could also use a mesh drainage material. Here’s a great article that describes the details of a good rain-screen layer:

      • Thanks Ted,

        Just to have all facts, It will be all brand new cedar siding, sealed on all sides. But the rest you got spot on.

        I love spray foam, did it to my kitchen cathedral ceiling, but for this project it’s not in the budget and doesn’t really work logistically for a spray foam contractor as it’s not like the building will be bare to just come and shoot. I will be doing the project myself over the course of probably many months little by little. So as the less expensive and DIY method I’ve decided on Roxul batts due to it’s moisture forgive ability, and mold resistance. Also it’s higher R-value and work ability than fiberglass.

        Now I’m glad you’re ok on the roxul and housewrap plan but hear me out on the rain screen idea. Even strapping out the studs 1/4″ on top of the house wrap before the siding will again effect the depth of siding vs. the trim. Something I’m really trying to avoid. So, because the Roxul is only 3.5″ thick and therefore leaving a 1/2″ gap to the exterior of the true 2×4″ studs…could I “wrap” and staple the house wrap around each side of the studs by 1/2″, therefore creating a rain screen essentially inside the stud bays? I figure as long as the house wrap at the bottom of the house is then feathered out over the water table drip flashing like normal then all flow ok? I know it won’t be perfect, say at the second floor beams where the house wrap will be back flush with the siding for 8″ or so. But it’s better than no rain screen, right??? It will be a little tedious I’m sure but if I can sort of have my cake and eat it too then I’ll work for it.


    • I get it, that’s a clever idea but sounds like too much work. Plus, all those staples in the house-wrap would provide a lot of opportunities for tears and water to get behind it.
      How about this. Fill up the bays, do the house-wrap flush and use spacers for the siding except just below the trim. The slight difference would be minimally noticeable (probably). You could do a dry-run, just tacking up some of the siding to see how it would look before committing to that method.

  4. HI Minh,
    You definitely want to give each bath a fan and independent duct with as short a run as possible before terminating out a roof vent. The vents are easily installed by a qualified roofer and should last the life of your roof. The problem with sharing ducts is that this necessitates longer runs, which provides more air resistance meaning the fans work less effectively. Also, if you use one bath fan and not the other, there’s the chance of blowing stale air from one bathroom to the other.
    The only time this doesn’t apply is if you have a single in-line fan, with a larger duct running through a single roof vent and a ‘Y’ to combine the inputs from vents in two bathroom ceilings. This can work quite well if properly installed and is much quieter since the fan is mounted in the attic instead of the bathroom ceiling.

    The humidity levels are indeed troublesome. As you noted, you’re in a humid environment and that’s likely the cause of the very high humidity that you’re measuring inside. That can be really tricky because humidity at those levels can really saturate building materials and be a real mold breeding ground.

    I generally wouldn’t recommend attic roof vent fans. I had one or two in my home when I bought it and was shocked by how much it drove up my electric bills. Natural venting should be all that’s necessary.

    Got to run. Post more questions!

    • Ted,
      In regards to bathroom fans, I also do not have one nor do I have any existing ducts running in the attic. My roof has quite a slope, and I think it will be harder to install through the attic, so I was looking into wall vents. Are there any known issues or cons vs. pros you can tell for wall vs. ceiling/attic fan/vent system one? What would prevent outside air from getting into the bathroom if I install a wall unit?
      Thanks as always!

      • Are you thinking about the type of fan mounts right in the bathroom wall and go straight outside? If so that’s actually an ideal situation. Just mount it high up near the ceiling because humid air rises and will accumulate at the ceiling.

  5. Hello Ted! We are going to be replacing radiant heat units that have been extremely expensive to heat our home and do not even keep it warm. We live in Kentucky. We were considering the fujitsu units until we read your article. What would you recommend instead?

    • Frankly, given the lousy support Fujitsu has given, I can’t recommend them to anybody any more.
      At the current time, Mitsubishi is the vendor of choice. However, Mitsubishi has the same type of warranty – if it breaks, even under warranty, you pay the labor, which is often much more expensive than the parts.

      Based on this, I would talk to your local certified installer and mention that you’re concerned about this warranty policy and see if they have any coverage that would pay for labor if the system goes down. Even if it’s a service contract, it would be worth it because it can cost $1000-$2000 to repair the units under warranty due to the labor intensive nature.

      • Ted, what is your overall opinion about radiant heating? I was actually researching it as a secondary source of heating for my house, but stumble across this comment. The primary source of my house heating is by steam radiators powered by heating oil, which is quite expensive 😦 I was surprised to read that WC Townsend said it was extremely expensive. Are there different types of radiant heating, maybe more modern ones that do not consume as much energy? Anyway, your thoughts on this matter are highly appreciated as always.

      • The trick is there are multiple types of radiant heating. One refers to those free-standing radiators that plug in your wall or are wired in to run totally by electricity. Those are efficient in the sense that they convert 100% of the electrical power into heat. However this is not cost effective in most places. The other type of radiant heat is the type where you have tubes under your floor that heat up the flooring. That provides a very comfortable Heat but it’s efficiency depends on the heat source for the water that circulates in the tubes. This can be from oil, gas, electricity Etc. So you have to research this specific details.

        I hope that helps

      • We had a very slow leak in one of our mini-splits which resulted in a loss of cooling almost 2 years after the installation and well past their warranty. Our installer diagnosed the problem, repaired the leak and recharged the system at no charge to us, stating their installation was at fault. I was shocked and very thankful for the honesty. The moral here is check out your business and reviews before spending a chunk of money. Great service is priceless.

  6. Ted, your website is incredible and scary in the way that good information can be.
    My family just bought our first house after 30yrs in the US and so I’m admittedly not the smartest house owner around. I’m trying to learn though.
    To the point: the top story of our home was cold compared to the rest, we consulted HVAC specialist; they used an infrared temp sensor-device and saw that the ceiling was very cold relative to the rest of the house. Peaking in the attic he discovered that the insulation was r15 where our region needs r37. Trying to save money, I bought put in atticat fiberglass insulation; around r37 worth. The problem is that I most likely blocked the soffit rafter vents. There weren’t any covers there, but I could see light from the outside coming in before I put the insulation in. I tried to put in some foam vent covers but the tight was so tight I couldn’t squeeze in. So I skipped that step. That was just this last week, so no mold yet. I’m just afraid of what I’ve done…
    Should I get a pro and have them put in the rafter vents covers, or can I compensate somehow? Powered attic ventilator?
    I appreciate your time.
    -Minh Nguyen

    • Thanks!
      It is indeed intimidating. When I bought my first house, I really knew nothing, and suffered because of it. It wasn’t until well into renovating our second home that I decided that it was necessary to become well educated in how homes and their mechanical systems “work.” It was shocking just how much misinformation our contractors gave us, and how authoritatively they spoke!

      To make sure I understand, you added some fiberglass and probably covered some of the soffit air vents?

      How else is the attic vented? Is there a ridge vent or vents at the gable ends of the attic?
      Also, are there recessed lights or other holes in the ceiling of the upstairs rooms that would allow lots of moisture to move from the living space up to the attic?
      Most importantly, are all the upstairs bathroom fans vented properly? Meaning, is there a sealed duct running from the bath fan to a vent on the roof?
      You can double check to see if there’s moisture problems during the winter because they become very evident due to water condensing on the underside of the roof or even freezing on nails poking through (from shingles). If you don’t see any indication of moisture buildup, you’re probably safe for now. But I would suggest paying close attention to the situation for the next few weeks.

      If you really filled in the area by the soffits with insulation and the insulation is tight against the underside of the roof, then I would suggest removing it from those areas because that can trap moisture against the roof and lead to wood rot. I understand what you mean by tight spaces because mine is like that too and it’s very difficult to get in those areas. Here’s a tip – get a small rake with a long handle. Then you can reach way down to where the soffits are and push the insulation away from those areas. Something like this could work well if you attached and extended handle to the existing one.You might be able to use a pool pole and just duct-tape the handle of the rake to it to give you a long reach.

      • Ted, I am incredibly appreciative. Thank you very much. Whenever the complexity of a house becomes headache inducing, I just try to be grateful to have a house at all. But anyways, thank you for your kindness and your time.

      • Hi Ted,
        I see 3-4 ridge vents. No gable vents. I see 2 small grilled openings at the top of the roof.

        No recessed lights.

        There are no bathroom fans. We open the windows. The humidity in the room still rises 10% to about 75% after showers. I’m about to install bathroom exhaust fans and will vent them into the duct system. Regarding this matter; i’m confused on whether I should get an inline system or just the typical ceiling mounted one…
        But no, there is not a sealed duct running from the bath fan to a vent on the roof. I take it this is far more desirable than running that bath fan to another duct which leads outside?

        No mold or freezing in the attic but the humdity sensor is about 85% now; this is probably affected by recent rains and the fact that we’re 5minutes from the ocean. But still, 85% does not seem healthy.

        I installed the soffit vents covers as per your instrucitons.

        Still, regarding the high humidity, do you think it’s a wise choise to get a powered attic ventilator? And if so, can I just attach it to the grilled openings at the top of the roof?

        Any suggestions you have on this matter would be much appreciated.
        Thank you for your help.

        Minh Nguyen

  7. Hi, Ted,
    I need an unbiased opinion. We have received 5 bids from contractors to replace our hvac heat pump system. We currently have 25 year old Trane 2.5 ton and 3 ton heat pumps and two air handlers heating a 1990, 4600sf, 2 story home. Our pumps are dying and our electrical bills are gigantic in the winter…$600 for December and January. We live in Washington State. We wanted to replace our 2 heat pump systems with one high quality heat pump, a 5 ton Bryant Evolution Extreme, with upstairs and downstairs zoning. It is not too difficult to combine the ductwork into one system, because our system has the air handlers with supply and return ducting all in one closet. It turns out that before the home was added on at both ends, the system had only one heat pump and air handler and the ductwork would have been one system. All of the load calculations have come in between 57,000 and 60,000 btuh which seems to lend itself well to a single 5 ton heat pump. Two contractors seem to think it would work well, one says he thinks it will work well, but we need to have a backup plan if it can’t meet our heating needs. Two others say that it needs to stay as 2 systems and would only bid it that way. One of the contractors (who didn’t supply heat load calculations but who has many great references) sells American Standard heat pumps and would not bid it as one system. He is adamant that two systems is the way it should be done. His cost is only $2,000 more for 2 systems than one of the 5 ton Bryant Evolution Extreme heat pumps. We’re looking down the road though and thinking we like the idea of one system when it comes to maintenance and repairs. We were thinking that if we seal our ductwork we could gain enough to give us the assurance that one 5 ton system would work here. Please share your opinion when you get a chance.

    • If it were my home, I would stick with two systems. Zoning with a large system would lead it to be massively oversized when only one of the zones is operating, possibly causing significant comfort issues and poor dehumidification ability. Two, smaller systems would be more efficient and more comfortable, as well as better able to handle humidity. In addition, I prefer multiple smaller systems because if one does break down, at least you’ve got some heating/cooling ability.
      Ultimately, when you make your choice, go with the contractor who comes with the best references and gives you the most confidence in their abilities to troubleshoot and support the system. In the long run, you’ll be happiest with a quality install and great service.

  8. Ted
    I love your web site. I’ve read almost everything you write. I have some questions regarding insulating cathedral ceilings in a rehab located located near Atlanta, GA. I have spent hours researching the best way to insulate my cathedral ceiling (to R30 or better). Almost all of the information that I can find deals with the wintertime issue of preventing warm, moist interior air from condensing somewhere in the roof system and causing damage and/or reducing energy efficiency. I can’t find anything that discusses what happens in the summer when the hot/humid air on the outside meets the colder air (from AC) on the inside. Do you know of any information that discusses roof insulation systems for hot/humid climates? I want to design an insulation system without using spray foam. Mostly because I’m wary of health issues. I am thinking of using one of the healthier materials like wool or denim along with some rigid foam to get the R value that I need. I like the idea of using rigid foam on the underside of the joists prior to drywall as part of the system. The project is a rehab with all old drywall and insulation removed back to the studs/rafters. Rafters are both 2×8 and 2×10 (in different rooms). The house has a metal roof with a ridge vent, but very poor (or non existent) soffit vents since the house has no eaves. Can you think of a way to insulate the ceiling that would use the ‘hot roof’ system using foam boards (XPS?) and/or wool batt insulation? If not a ‘hot roof’ system, do you have other suggestions or ideas for a design?
    Thanks and Best Regards

  9. Hello,
    Do you have any ideas on why new upvc double glazed windows (argon filled, with warm edge spacer and thicker profile than old ones) are giving off so much convection draught. The windows are definitely sealed up and close tightly. Of course I’ve done all the usual things like install blinds and long thermal curtains, but in my previous house with basic double glazing I had no need to go to extremes, in fact I just used lightweight curtains for privacy and there was no draught at all. Since moving to this new house, it’s been an absolute misery; not because it’s cold; British houses generally are, but the constant draughts make it difficult to be comfortable even with the heat blasting. I have done everything I can regarding draught proofing and insulation and have realised it is probably the constant waves of convection from the windows which is making the whole house draughty. I have never known this even in an old Victorian house with wooden windows and single glazing, so it is really strange as to what is going on with this house; the contant ‘moving air’ means it’s just like trying to heat a house with all the windows ajar! Any sort of feedback would be most welcome!

  10. I have a 35 year old post & Beam home with a vaulted ceiling, at times I do have a moisture problem. I have about 14″ of cavity wth 2-6″ fiberglass bats. I’ve been told to add ventilation (there is none now) – I’ve been told not to ventilate but dense pack with cellulose- I was told to install rigid foam board on top of the existing decking & add new decking & shingles ( which I lean towards because the shingles need replacing anyway). The ceiling is 1×6 t&g so there is plenty of air leakage. I would appreciate your input. John

    • The critical component with a tongue-and-groove ceiling is to make sure there is a air / moisture barrier directly behind the boards so that moisture is prevented from entering the cavity. Without that barrier the moisture will pass up through the insulation whether it is cellulose or fiberglass and then come in contact with the cold roof deck where it will condense into liquid water and that’s where the problems really begin.
      Rigid foam board on the top of the roof deck can help keep the roof deck slightly warmer reducing the chance for condensation however I would consider it a risky solution with the insulation inside the cavity as well because so little heat will get through that layer of insulation that the roof deck will still get very cold and you risk the same condensation problems.

  11. hey ted , you have helped me in the past with heating / cooling questions and would like to pick your brain again. we had installed a central air system with heat pump for a vacation cottage to eliminate my antiquated oil burner system. so we have forced hot air that i leave on about 53 to prevent pipe freezing over winter . not sure if you remember the case. anyway, that is doing fine for doing the job but just recently had leak from water pump coupling that failed as far as i can tell. my questions are about radiant floor heating. we are on a slab and the way it looks my 3 bedrooms will need all new carpeting and my living room with laminate flooring looks to be ruined as well from about at least an inch or water on it for i dont know how long. i was planning to redo all flooring with tile to avoid ripping up wet carpet ever again . i thought this could also provide opportunity for nice radiant floor heating in winter weekends when i am there because the forced air heat in overhead registars makes me miss radiators . the air is clearly cooler down on the floor. not a disaster but maybe spend a little more now to make the home more comfortable and as you get older easier then constantly feeding my wood burning stove for heat on those cold weekends. is this a big job to put is 3 bedrooms and living room to use as needed, not main heat source or is it probably not worth it? kitchen /hallway is already tiled so have some concerns abouts it also raising height of floor in those rooms, possible tripping hazard? any thought . thanks again hope holidays went well bruce

  12. Hey Ted,
    First off – great info on the site! I live in a 1950’s townhouse that has a brick exterior and plaster walls with an air gap in between (as described in point #4 in your “How NOT to insulate your house” post). I’m working on adding some extra insulation to the attic and noticed that this gap extends all the way up, where I thought there would be a top plate.

    Currently, there’s loose-fill insulation that covers the air gap along the outer walls of the house. Can this gap be left covered with insulation, should it be uncovered and open to the attic, or should I follow a different approach?

    • That’s always a tricky one. Often, these gaps run all the way down to the basement which is a problem because that draws relatively warm, moisture laden air from the basement and dumps that moisture onto the underside of the roof sheathing. This can then condense and rot out the roof. It can also cause ice dams by melting the snow on the roof above. In those cases, I usually like to see the gaps sealed in the basement but left open at the top which allows some “air flushing” but draws the air from the outside which poses less moisture/heat risks than basement air.

      To answer your question – best to leave these gaps uncovered in the attic. For the most part, I don’t like messing with original construction techniques from that vintage if there haven’t been problems.

      The one thing you could do is install vent chutes under the roof deck and blocking to prevent insulation from getting out to the soffit area and minimize the chance of the insulation trapping moisture against the roof. Here’s a great article covering this in detail.

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