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!

Note: all comments are moderated unless I’ve approved one of your previous comments. Almost everybody gets thrown off by this, but I moderate comments to avoid spammers. The downside of this is that you won’t see your comments post until I’ve had a chance to review and approve them. Sometimes this can take days (sorry!) Thanks for your patience.


1,317 thoughts on “Ask Ted!

  1. Seams like this is the place to ask a question and get an answer that helps!
    I have a home built in 42 in PA I am renovating. The attic was converted to living space and had a few other renovations like 2 renovations small doggy dormers on the south side and i will be adding a small dormer in between the 2 on the backside to expand a bath. The situation is I have 2×6 roof rafters and R19 compressed over a 2” thick rafter vents. I have a roof done in 09, and ridge vent that is maybe 20ft along the roof line that is 35 or so ft long. No soffit vents.
    With the dormers, vaulted ceilings, short ridge vent, compressed fiberglass insulation not properly sealed, no soffit vents, and now adding a new dormer, what are my options to correcting this mess?
    One option is extend ridge vent, add soffit vents, pad out the 2×6 with 1.5” strips, 1” air gap, .5” pollyiso, 5.5” mineral wool, sheet rock. takes me from compressed fiberglass R19 to an R26 sealed, mineral wool, pollyiso foil faced radiant barrier?
    Another is doing soffit vents, ridge vent extension but doing 5” of polly iso and .5” of air gap space and not loosing head height and going to R32?
    Last option remove ridge vent, seal it, not getting soffit vents, mineral wool R23 and before i put up sheetrock another .5” of Pollyiso cross grid over 2×6 then sheet rock?
    Last option is ridge, soffit, only .5” airgap, then 1” polly iso, mineral wool, brings me up to R29.
    Not doing spray foam because cost and not able to find a rep in area that has a removal clause if its not installed properly in contract.
    Any other option?

    • It looks like you’ve come up with some viable options.
      Option 1 I’m not keen on because the 0.5″ polyiso will be a vapor barrier on the cold side of the cavity insulation, so any moisture that gets into the cavity will condense on the inside of the polyiso. Ideally, you’d want the vapor barrier on the warm side. If you increased that to a 2″ thick slab of polyiso, and less cavity insulation, that would provide enough insulation to greatly reduce the chance of condensation on the polyiso.
      So, for that reason, option 2 is preferable. 5″ of polyiso would block moisture migration and provide excellent insulation. It’s a little pricier, but it should work well and have little chance of moisture getting stuck in there. That you can DIY and it would be as close to doing spray foam without the concern about improper installation/outgassing etc.

      • Wow fast reply! Thank you! So to make sure my homework was going on the right track and I understand this,

        is keeping a 1” air gap better than shrinking that to .5” or is the actual dimension of the air gap that important? What about the 2” tall styrofoam or plastic pre made vents they sell? Why 2” tall?

        In reading the part 2 of the insulation post you said sometimes ridge vents are worse. So if i am adding another doggy dormer to the cathedral ceiling and basically removing more rafter vents from the cathedral roof, would it be smarter to remove the ridge vent entirely, not install soffits and insulate entire cavity? Or am i correct in saying even a few properly vented rafter bays are better then none?

        Lastly is about my middle cost option of polly against the cold side and rest of cavity with mineral wool? That goes with the first part of either a 1” air gap or a .5”. Lumber dimensions playing into it, the max I feel comfortable furring out the rafters is dimensionally 1.5”. So with mineral wool being 5.5” i have that 1.5 to make air gap with the pollyiso board. So if .5” air gap is acceptable then I would use the 1” polly board, then 5.5 of mineral wool to get me to R29 at a reasonable cost compared to all polly board. If a 1” air gap is minimum size and my rafter bays are not 16” center more like 18. But if I need a 1” air gap minimum, then that only leaves me .5 pollyiso, then 5.5” mineral wool. Still way better than Fiberglass r19 compressed over a 2” tall rafter vent in there now. But the best performing option and less work but more $ is the full pollyiso board stacking i have come up with?

      • I’d keep the ridge vent, ideally extending it to full roof width and add soffit vents. That Cor-a-vent product is excellent and one of the few that provides enough airflow.
        The case where the ridge vent makes things worse is typically with an open attic space and no place for air to come in other than getting sucked from the house. This doesn’t apply in your situation if you add soffit vents. If you don’t have vents, then there’s no physical mechanism for the air to enter the cavity and flow out, so moisture would have to move out via diffusion rather than air flow. Not desirable.
        The size of the gap is important. When it gets too small, the air flow through the cavity is restricted as the aerodynamics start getting unfavorable for smooth flow. 0.5″ is pushing it. 1″ is minimal. 2″ is “the standard” though 1.5″ is fine.
        It’s best to do things “by the book.” Even though this space will be hidden from view, building inspectors can be very picky, since they are literally “going by the book.” They’re also a good resource and befriending the local inspector can be helpful during a project as they can give you tips and keep you out of trouble with your local jurisdiction.
        Those foam vent inserts work, sort of, but they’re very flimsy and the cost adds up. My preference would be to use 1×2’s, tacked along the roof joists/rafters (tall direction for larger gap) then insert the foam board to those spacers. You could cut strips of foam board also and just use construction adhesive to attach them to the rafters. The problem with the foam board is that it gets crumbly when cut into thin strips. But whatever method works for you that provides a backing for the larger foam board inserts is good.
        On the last option, I’d really stick with a full 2″ of foam board on the roof side of the insulation. The “rule of thumb” is that you want as much R-value of foam board as you’re putting loose insulation in so as to avoid that interface being a cold surface which can form condensation. But the specifics of course depend on how cold it gets. You don’t have to worry about a little insulation compression as the R-value per inch actually increases with compression, so the total R-value doesn’t drop too much. The rules about compressing insulation are mostly about using it in other types of spaces where the compression leaves gaps and voids. I wouldn’t sweat that. You can also buy “high density” batts which are higher r-value per inch because they are already compressed!
        Hope all this helps. good luck with the work.

  2. Hi Ted…

    We just purchased an old house (we think it was built in the 1940’s, but maybe later), but also looks like it may have been through some kinda of remodel later – we’re just not sure. Anyway, we would like to insulate this house – and I’m reading horror stories about insulating an old house. I put pictures for you to see here….

    Have any words of wisdom insulating? The siding seems tight, has an asbestos siding and that has been covered with vinyl siding. Reading the horror stories, I’m thinking I just live with it, tear down these “cardboard” type walls and replace with a bathroom type moisture resistance drywall and leaving the wall cavities alone.


    • If you’re going to replace the existing wall material, that’s a great opportunity to really work on the interior insulation, wire running and so forth. Most standard walls like those just use normal insulation products without problems but YMMV.
      If I were doing that for my own house, I’d spray in high density foam insulation (if I had the budget) which would be the safest bet as it’s extremely tight and minimizes moisture movement.
      If you’re going for a more DIY solution, many are now opting for Rockwool insulation, but standard fiberglass is fine. Not my preference, but when installed properly, it works. As an added layer of protection, a 1/2″ foil-faced poly-iso foam-board installed over the studs, before the drywall. This might require re-mounting outlets and extending window jambs, but it seems like you’re doing an extensive remodel so this might be feasible. Putting the interior foam board has multiple advantages of further reducing moisture migration and reducing thermal bridging at the wall studs.

  3. Ted,
    I have an interesting project that I could use your insight on. I’m building a tray ceiling in my bedroom. I’m doing that by essentially building a 2×4 frame around the perimeter of the room. It will only end up being 3.5″ thick with drywall. My initially thought was to put pink rigid foam in the top of the perimeter build up, up against the existing drywalled ceiling, but then I got to wondering if I would be creating a double vapor barrier, even though rigid isn’t fully vapor impermeable. From the attic down the layers would be: fiberglass insulation with paper vapor barrier, painted ceiling drywall, rigid foam, 2″ air space created by empty framing cavity, drywall on bottom of tray framing, room space.

    Do you think I would create an issue lining the tray with rigid foam up against the existing drywall ceiling, or is there not going to be enough moisture going either way to cause a problem?

    Much thanks as always!

    • Hey Andy, happy New Year!
      Another great question. I would think there’s a slight chance of that issue, especially at the seams of the new insulation, but if you’re meticulous about sealing joints, there probability of problems with this construction would be minimal. The rate of moisture transfer is very slow. The moisture would pass the board-foam, go through the painted sheetrock and into the space under the fiberglass facing and get trapped. But, since the fiberglass facing is a poorly sealed system, it seems like any moisture would be able to slowly diffuse into the attic and out.

      of course, YMMV, and you’d want to be doubly careful around any penetrations through the ceiling, but generally, this doesn’t sound very risky.

      • Hello Ted,
        I hope this is the proper way to post a question / ask for your advice. I have a 16’x 16’ enclosed, uninsulated, walkout patio that I’m looking to use as a three / four season room. It has a 4/12 pitch 2×8 cathedral cieling,( about 12’ from concrete slab floor to ridge). The house side gable end will be a three panel, double pane patio door, the other 3 sides have a brick knee wall with large single pane patio enclosure type sliding window / screen units, and an entry door. I am currently installing a very small wood burning stove to take the edge off during late fall and perhaps favorable winter days. It is being piped through the ceiling with a rafter mounted support box.
        The room is soffited, fully on one side, and 3/4 of the other side wall. It also has a ridge vent. I am going to install cedar t & g as a ceiling and was wondering if it would be better to not insulate at all, leaving the vented air space between sheathing and t&g? I suspect condensation could become an issue if the stove really heats up the room with a cold roof. I’m not against doing a full and proper ceiling insulation job if that is the best practice, even though the rest of the room is uninsulated. I would appreciate your thoughts, thank you!

      • Hi Mark, these types of rooms are really challenging. With all the glass area, the heat loss is incredibly high. You might consider an infrared radiant type heater. The wood stove will serve that purpose to some extent, but if that’s insufficient, ceiling mounted radiant systems are so convenient and deliver heat right to your body. Just a thought – I see a lot of those in al-fresco dining places and they’re highly effective.
        So, back to the insulation. you might consider shiny, foil faced polyiso board foam under the rafters, with an empty cavity above – foil facing up to the empty cavity. This won’t do much in the winter because of all the other heat loss, but in the summer, it can help considerably to avoid baking you from a hot roof. Plus, if you tape the seams carefully, it will greatly reduce moisture getting up into the cavity. Over the foam (under, from the perspective of the room) you would install nailers across the rafters (mark the position of the rafters on the foam so you know where the centerlines are. Studfinders may not work through the foil) and then install the T&G cedar to those.

      • Ted, Thank you for your thoughts. I will look into the infrared heater option. I did want to ask your opinion on the aluminum foil type heat reflecting materials, especially the non perforated varieties. They claim to reflect 97% of the heat and are also a vapor barrier. As the material is double sided would this work “both ways” applied between the rafters and t&g ?

      • Radiant barriers are only effective with an air gap of at least 1-2″. Closer and you get more conductive heat transfer so they lose effectiveness. I put it under my garage roof and it keeps the garage attic space much cooler. Still quite warm, but much less than without.

    • That’s a good insight, Andy.
      While I wouldn’t guarantee anything, I think you’re safe doing what you’re talking about because the inner surface of the foam will be warm which should greatly reduce the condensation potential for the cavity between the new inner ceiling and the foam. The painted sheetrock should allow a very small amount of moisture transfer into the cavity and then the moisture level should reach something of an equilibrium at about the average humidity of the interior of the house. Unless you have extremely high moisture levels in the house (high enough that condensation forms on the ceilings), the condensation shouldn’t form on the foam.

      • Ted,
        I hope this email finds you well and you’re staying safe and healthy! I’m working on air-sealing and insulating my attic, still. Original R19 insulation from construction in the early 70’s. I’ve been pulling out the old R19, air-sealing and reinstalling new R19, then a layer of R30 on top. It would be much easier to blow in fiberglass loose fill and then go over that with batts of R30 but I wonder about a vapor barrier? Also, I believe that I read that loose fill has a lower R value per inch than batts? My mom’s condo (built in the early 2000’s) has all blown in fiberglass and no vapor barrier. Blown in right on top of the drywall ceiling. Is this a big no no? We’re in Michigan.
        Thanks in advance!

      • Vapor barriers are a topic of much debate. In colder climates, they’re usually proscribed because of the greater chance of moisture getting into the attic and rotting out the roof.
        The first thing I would do is contact your local township office and find out if your building code calls for it. Always follow local code because if you don’t go “by the book”, you can have trouble when you sell your home. Inspectors look for code violations.
        Generally speaking, if you do a good job sealing air leaks, and the attic is well ventilated, you don’t need vapor barriers in any but very cold climates. The trick is proper air sealing. The easiest way is to have a thin coat of spray foam applied before any insulation. This seals everything better than you can by fixing them one by one. Then you can blow in lots of insulation on top of that. Blown in can be very effective because it settles down and fills in all the nooks and crannies around odd shapes much better than batts. Batts can work well but can be labor intensive to do well.

      • Ted,
        I hope you and your family are staying safe and are well! I’m currently working on insulating the walls of my basement with either 1.5 or 2” rigid insulation. One entire wall of the basement has my garage on the other side, and half of another wall has an addition on the other side. My question is, with the other side of the foundation in these areas having a structure over them to protect them from rain, snow, exposure to the elements, etc., is it even beneficial to insulate these areas?

      • Thank you Andy, it’s always good to hear from you. I hope you and yours are also doing well.
        Another good question. So the question is, “Is it necessary to insulate walls that have conditioned space or partially conditioned space on the other side?”

        Typically, walls separating homes from the garage should be insulated since the temperature swings of the garage can be extreme. Additionally, adding foam to the walls will help to greatly reduce the movement of any noxious vapors from the garage into the house if the walls are at all porous.

        The other area which has an addition is probably not worth it. But it depends. Is the basement kept at normal home temperatures? Some people keep basements unconditioned, in which case you want to minimize heat flow through the wall from the living space into the basement. However, it’s complicated. If you have an unconditioned basement, adding insulation can allow it to get too cold, leading to mold or freezing problems. So I’d suggest carefully evaluating the thermal dynamics of the spaces before you decide about insulating.

        Hope that helps. Thanks for all your interesting questions!

  4. I have some questions, is this where I ask? It’s about a remodel job and now I’m seeing a problem with moisture……

      • Ted,
        I have accomplished phase one ( sealing all cracks/ openings in ceiling between living space and attic). Today I am going to buy the gable vent and get that installed after painting.

        Thank you for the advise.

    • Sorry, new at this but I think I see this is where I ask my questions…..

      My wife and I purchased the house her father built in 1965, he was an iron worker and he built a butler building and modeled it in to a home. This home is made of Iron beams and steel roof and siding and suspended ceiling throughout the house. We had the house remodeled about six or seven years ago and all the ceilings were torn out and replaced with wood rafters and drywall. In our living room we had cathedral ceiling built….
      The ceiling in the living room is built to the slope of the steel roof and the area between the roof and ceiling is packed with fiberglass insulation…..the steel roofing has insulation backing as well.
      We have a spot on our ceiling that is growing, ceiling texture is peeling back and the wet spot is continuing to grow….I went through the access opening to the attic and discovered moisture forming droplets on the steel beams up there….the areas where there is no cathedral ceiling looks fine in the attic, I cannot see into the area that is cathedral……I’m sure there is absolutely zero air flow in this area…..
      Any suggestions?


      • What’s probably happening is the cathedral area is insulated, so the area between the insulation and the roof is colder. That’s the point of the insulation and is expected. But, the colder it is, the more likely condensation will form. It’s a Catch-22. You want good insulation to keep the heat in the house but the better the insulation, the more likely that you’ll get condensation above because you’re losing less heat.
        So, in order to minimize moisture getting into the attic, you need to do two things: form an essentially air-tight seal between the living space of the house and the attic and, since that’s never perfect, you have to ensure that the attic is well ventilated with outside air.
        Outside winter air is typically very dry, so flushing the attic with this air helps get rid of moisture from the house that gets into the attic.
        This shouldn’t be done actively with fans which can create too much ventilation and actually worsen the problem by sucking air from the house into the attic. It should be done passively using venting. These days, practice is to allow air under the roof deck with continuous soffit vents. This is complemented by a continuous ridge vent, allowing air to flow freely up the soffit vents, under the roof and out the ridge.
        Any “hole” between the living space and the attic space can allow lots of moisture into the attic. For example, that attic access hatch is usually one of the worst offenders. It should be sealed with a heavy door and compressible weatherstrip that seals tightly. This single thing can make a huge difference. You really want to scrutinize the attic. Look for where the most condensation is forming on the steel beams then look at the floor underneath that area. Are there any holes? Any pipes coming up through the walls? Seal everything. Imagine that you’re building a submarine. Any place water would be able to seep through is an area that should be sealed.
        Even if you do your best job, there’s still a chance that you’ll get some condensation. The steel is an extremely good conductor of cold, so it will quickly reach the outdoor temperature. Often, I’ll see ice form on steel beams or roofing nails. This ice builds up during cold spells. Then, when you get a warm spell, the ice melts quickly, leading to water damage as the water drips down. It’s very difficult to solve 100% but if you address the two issues mentioned – keeping moisture out and ventilating well, you can minimize the problem.

  5. Hey there, we are reno’ing a 1970 built wood frame bungalow. We are replacing the vinyl siding with either acrylic stucco, hardy board or

    Whatever we choose we are planning to cover the house with 2 inch rigid foam insulation. Just wondering whether we should cover the gable at both ends and front portion, to maintain a level surface for the siding? Otherwise we will have a 2 inch gap to fix.

    • If there are existing gable vents and you haven’t had issues with the attic in the past, I wouldn’t mess with the venting. When I redid my house and added 2″ exterior foamboard, we installed a new gable vent, flashing it around the foamboard so it was flush just like it would be to the plywood exterior walls. Then we installed the siding. So it looks just like a normally sided house.

      • Thanks. That makes sense but I was thinking more on how to adjust for the fact my main wall will be 2 inches thicker than the gable area if I don’t extend the foam board up to the gable area. Don’t think it would look so bad but being 2 inches thinner, the intersection will need a bit of adjustment

      • Why not use the 2″ foamboard everywhere. You just have a cutout for the gable vent and install it over that so it’s flush with the rest of the siding.
        You also would want to do this in order to have proper flashing and drainage.

      • Thanks. I was thinking that as well just wanted to make sure wasn’t missing anything.

        We were going to just blow in additional insulation into attic but the popcorn ceiling has been painted over which has made it very difficult to scrape off. I think we’re gonna pull down the drywall, remove the thin layer of (brown) blown-in insulation and start over. Put up new drywall, good vapor barrier, spray insulation for the holes and gaps followed with blow in insulation. Tough to say no with the more research one does regarding proper insulation but with new windows its probably the right call.

        Great info here regarding doing insulation right. Thanks!

  6. I have a vaulted ceiling with a skylight. I keep getting mold and condensation on my ceiling. I have had my roof and ac unit checked out and they are fine. Air isn’t circulating and causing mold. Humidity levels are high in North Carolina summers. Would it help to install ceiling fans?

    • A ceiling fan to move the air around will certainly help. There’s no guarantees but it’s a good start. You really just want to move the air around to help evaporation before it can do any damage.

  7. I have recently started learning about building science on the internet. It started when my Ac went out and I learned I could fix it with just a capacitor. We have a ac that has struggled to maintain set point in summer and winter. After cleaning both coils and having the ac system checked out, I moved on to learning about the ducts. Since then I have learned my ducts were not sealed with mastic, the air handler had holes, and the flex duct is sagging and to many bends on some runs. I have also learned that the house is not air sealed at the ceiling. This leads to my question around air sealing. Everything I have read says air sealing the top plates, supply registers, all of the can lights, etc will have the largest effect on cutting down the drafts and energy usage. I am concerned about air ceiling the top plate on the exterior walls though, because I read that the exterior walls need to be able to dry any water that may get in so they need air movement. I live in the southeast, so we air condition most of the year which means moisture is usually moving into the house. I’m sure I’m missing something, but I am worried about reducing air flow on exterior walls if I seal the top plates. My home was built in 2000. 2800 sq ft. Single story with slab foundation. Ridge vents with inlet vents under the eaves. Ductwork in attic.

    • The main issues I’ve heard about is with balloon framed exterior walls behind stone/brick facades. With these, there can be moisture drive that forces moisture into the cavities which then is allowed to flush out. However, even in this case, these walls typically start in the humid basement and end in the attic, encouraging moisture from the basement to flow up through the walls and into the attic. In cold climates, this has a tendency to rot out the roof where the moisture comes in contact with the roof deck.
      The double-edged sword of allowing the top plate to ventilate is that this induces even more air flow through the walls which sucks more moisture into the walls. Sealing the top plate reduces the flow, creating more of a dead air space.
      That said, extremely humid, warm, environments have different considerations than more moderate climates where condensation and cold are the primary issue. If you haven’t had any moisture problems in your exterior walls, then I’d be inclined to say “don’t mess with them.” and just do your best to seal recessed lights and interior wall top plates, pipe penetrations, etc.

  8. Hi Ted, I saw an update to your 2014 article which upgraded your thoughts on Fujitsu mini-split air source heat pumps to neutral. I was wondering if there was a manufacturer of ductless multi-zone systems that you could recommend from a reliability/longevity/efficiency standpoint?

    • At this point, it appears that both Fujitsu and Mitsubishi have longer warranties and a pretty broad dealer network. Mitsubishi is really the gold standard. But even perfect equipment will fail if not installed well. So I would emphasize the selection of installer is the #1 factor. I’d make sure to get their warranty/replacement/repair policies in writing and be sure you’re comfortable with the installer. This might be a one-man shop or a big company. You have good and bad across the spectrum. The main thing is experience and good reviews for customer service.

  9. Hello Ted, thank you for sharing your knowledge and educating the general public on these complex topics that affect our biggest investment…our homes.

    We had a pretty serious rain storm last night here in the MD/VA/DC area and it has exposed a problem I see with my roof. The drywall under a vaulted ceiling got wet and dripped into our living room. I got up on the roof to see where the issue was and found all of the shingles in tact. All of the vent boots in good condition, and not immediate issues I could see. I walked over on the roof to where the problem area was inside and found that the sheathing has a lot of flex and is bouncy. A lot more so than anywhere else on the roof.

    I did some research and came across your article on mold and vaulted ceilings. I have a feeling this is what I have going on. The roof looks to be relatively new but I know the root problem has probably been there for a while.

    I am afraid that if I call a roofer they will just put new sheathing and shingles on and not address the root cause. I tried looking up “residential building science services” in my area but I am only getting attic and crawlspace insulation services. How can I look for a building science professional in my area that can look at my situation and advise on a plan that addresses my root issue?


    • Hi Jay, it definitely sounds like the roof deck is getting weak and likely from some sort of water issue. If the top of the roof (shingles etc.) looks sound, maybe the wind was actually driving rain in through a ridge vent or some bad flashing higher up on the roof, like at a chimney? I had a very similar incident at my house last winter where I started seeing a couple wet spots on my ceiling. I traced this to two areas of flashing that looked ok but weren’t large enough to stop water from getting underneath and working its way into my ceiling structure. It’s also possible that this, repeatedly occurring over time could have wet the roof deck enough to cause it to rot out. So I’d double check all that before getting too nervous.
      As for your real question – locating building science professionals, you might try an organization like:

      Infrared inspection can be very effective at tracing the source of moisture issues and also people who do this type of testing often have other troubleshooting skills.
      Make sure to check into training. Lots of “guys with trucks” buy infrared cameras these days but don’t have the training to really understand how to interpret the images.
      This company:
      looks promising also as I have a soft spot for companies that publish meaningful information about troubleshooting. It tells me that they like helping people.
      Another possibility is an energy auditing company. That’s how I started selling my services before specializing in troubleshooting
      A “good” energy auditor is really a home troubleshooter and should be capable of helping you track down these issues.
      I also look for independent companies that aren’t just franchises. I find independents are more in it for a passion of their field while franchises are more about the money.
      might be a possibility. They’ve got the right certifications but I can’t tell how experienced they are.
      I hope these leads help. It can be really challenging tracking down someone qualified, but it does look like you’ve got a handful of possibilities in your area.
      Good luck!

  10. Hi Ted, Love your articles. I just bought a cape style house with knee walls that need to be insulated properly. They are great storage areas so I would like to keep them as conditioned space. My only issue really is that the knee wall space is not ventilated (no soffits). It is under the actual attic and shares walls with living space. I plan on insulating under the roof deck (rafters) with R19 batts, then rigid foam board and then a sheet of radiant barrier; and doing the same with the knee walls themselves. I will not insulate the flooring. I was thinking of putting venting baffles in the rafters between the batts and the roof deck but Im not sure if its necessary or not. I don’t want to trap moisture into my insulation. Thoughts? Thanks!

    • Thanks Todd.
      Those knee wall storage areas can be problematic, however, it seems like you’re doing your homework and can avoid some of the biggest issues.
      The first thing is, avoid the double-insulation issue. Either insulate under the roof deck OR insulate the knee wall and floor section, but not both. If you do both, then the storage space behind the knee wall will get cold and the moisture that will get in there will be much more likely to condense and cause problems.
      It’s definitely a good idea to use baffles or another method to ensure an air gap between the batts and the roof deck. You want to ensure that the batts don’t trap moisture against the roof or you’ll certainly have moisture problems.
      If you do as you noted, and add foam board on the inside of the insulation, across the beams, that should go a long way towards preventing issues, but you need to do the job carefully. Instead of using the foam board and a radiant barrier, you could just use foil-faced poly-iso board foam. The foil facing will block all moisture and if you’re careful to tape all seams, you’ll minimize moisture transfer. You still have to be careful to ensure that there’s no gaps or places that air could get behind the foam and trapped in the cold roof cavity. On a retrofit like this, that will be challenging, but doable if your access is good. An attention to details is key. Think about it like you were building a submarine and the only thing stopping the water was that foam board. If there are any gaps where the water would seep in, you’ve got problems.

      If all is done carefully, then any small amount of moisture that gets in may be able to diffuse out slowly before causing damage.

      • Thanks Ted, With that iso foam board, would the reflective surface be facing into the conditioned space or out towards the roof? Inward right? Would you recommend any radiant foil material with perforated holes on the knee walls themselves, where you said to take out all other insulation? Thanks!

      • I Todd, you’d have the foil face inwards. The rule is the foil facing will do the same thing facing either way as long as there’s an inch of gap between it and any other material. There’s foil facing on both surfaces of the foam board but usually only one is shiny, so only the shiny side acts as a radiant barrier.
        I wouldn’t do anything with the knee walls if you adequately insulate under the roof deck. Just let the space behind the knee wall get to interior temperature and treat it like a normal closet in the house.

  11. HELLO TED,




    • The moisture is very likely coming from inside the house, not outside since the mold is forming on that beam. I wrote extensively on this in a recent article that you can find on my homepage.
      Humidity at the ceiling is higher so that 47% in the living space is higher at the ceiling. If the beam gets cold at night, water can condense on it.
      You could try blowing fans at the ceiling to circulate air and speed up evaporation. If you have a ceiling fan, use it to help air circulation.

  12. I have a metal roof over a vaulted ceiling. Condensation has created mold. After having company remediate and restore, the mold is back. I am told I need ventitation. The roof is tongue and groove; rafters are 16″ apart. Is it possible to ventilate without an attic? What do you recommend?

    • Again, apologies for the delay in responding.
      If there’s nothing underneath the T&G (between that and the insulation), I hate to say it, you’re in trouble.
      T&G provides zero resistance to moisture from the house getting up into the ceiling cavity. As such, even adding ventilation above it will do little to improve the situation. In fact, it can make it WORSE because the ventilation will increase the flow of humid air from the house into the ceiling cavity.

      The real solution is to pull down the T&G and install a vapor barrier between the rafters and the T&G ceiling. My personal preference is installing a layer of sheetrock, or better, foil-faced poly-iso foam board, across the rafters, taping the seams with foil tape.

      Also, if you have any recessed lights, those can allow a lot of moisture to flow up through them and into the ceiling cavity. It’s best to have an airtight ceiling and use fixtures that are fully inside the ceiling – i.e. no holes cut through the ceilings.

  13. Hi Ted,
    I have been trying to get rid of a musty smell in my daughter’s house in the deep south for several years, unsuccessfully. The smell gets in your clothes very quickly. Everything smells after an overnite stay. Vinegar in the washing machine removes the smell. It is a 1940s 1400ft2 conventional foundation house. Painting over the years has stuck most windows shut. She has 2 indoor cats. I built a trap door connected through a window to an outside cage to allow litter boxes to remain outside the house. She has washed walls with chemicals. Air conditioning system is new although ducts are not. I installed a whole house dehumidifier 6 months ago to keep humidity about 50% (used to be about 75%). No change so far. I tried an ozone generator – it gets rid of the smell for a day or less. As my next step I am considering an energy recovery ventilator to compensate for the closed windows. Do you think such a ventilation system might take care of the problem? Do you have alternative ideas? This is driving me nuts. Thanks.

    • Apologies again for the long delay.
      Smells like that can be maddening and difficult to track down.
      The key is to track the source of the musty smell, which is usually mold somewhere.
      Is there a crawlspace under the house or some other space that could be getting moldy? Often the odors will flow up from moldy crawlspaces and into the house.

      The dehumidifier was a great idea – you definitely want to keep the humidity low. Keep using it. 75% is well in the “danger zone” (anything above 60% makes mold happy).

      The ventilation system will certainly help make the house air fresher, even without the musty smell, it will help with those windows that can’t be opened. And it seems like a good idea as long as you keep searching for the source of the smell. The reason is that fresh air is a band-aid. The mold, assuming that’s what it is, will keep working. And, if it is mold, it could also be indicating rot. I’ve seen floor joists and wall studs completely rot out leading to homes that were structurally unsound, so you definitely want to find the source!
      Hope this helps!

  14. Hi Ted.
    I had closed-cell insulation sprayed on the underside of my new roof 4 years ago. I had ice-and-water shield installed as well completely covering the outside of my roof. The insulation ended up not being directionally stable and pulled away from some of the beams leaving some small gaps allowing humid air to hit the underside of the cold roof, condense, drip down, and cause some small water stains on the cathedral ceiling. Almost all of the problem seems to be at the peak of the ceiling

    The insulation installer came back with a thermal gun to find the gaps and drilled several holes in the ceiling. He then shot OPEN-cell insulation through the holes. He chose that OPEN-cell because it travels better to fill in the gaps and would be less likely to crack the ceiling. I questioned that choice because water vapors can penetrate that type of foam and I have ice-and-water shield which cant be penetrated so water vapor could still be an issue. He said that he wasn’t worried about that because the gaps were small and there wouldn’t be enough water vapors to cause a lot of damage. I went along with the plan because he agreed to cover the whole repair with his own money.

    That was a year ago. Over the last year, I have constantly monitored the humidity in my house and consistently ran dehumidifiers. I also had a timer put on my top floor bathroom vent so it kicks on for 10 minutes every hour. I’ve done all I could and the problem still returned. I’m assuming my insulation installer will return to take another look but I’m afraid we won’t have a great solution. I obviously don’t want a complete tear out as it would be very disruptive. I want things to be done correctly but in the easiest way possible. I also would love to not have to check my humidity levels 10 times a day. It seems like something I shouldn’t have to worry about.

    Do you have any ideas, Ted? I would LOVE to hear them.

    Thanks for reading this.

  15. Hi Ted,

    I stumbled upon your page on moisture problems with cathedral ceilings and am wondering if you would mind commenting on my situation.

    I bought a home about 6 months ago in Charleston, SC that was built around 1850. There is a cathedral ceiling on the second floor on which mildew started growing (and later, drywall started peeling) at the top of the ceiling around mid-March of this year. There are a few things I think might be causing the problem. First, there is no return HVAC register upstairs, so hot humid air is rising and stagnating near the top of the ceiling. Relative humidity upstairs is between 60-70 and temps so far get up to the low 80s, even with the central air on (although it wasn’t warm in March when the problem became visible). Second, the ceiling fan is poorly sealed and the hot humid air is escaping into the ceiling cavity. I didn’t realize how much of a problem this is until reading your article. Third, it’s an old house and I’m sure some air is getting in and out around windows, doors, and walls although the home is in good shape overall.

    I don’t have any knowledge of the roof design or insulation levels up there unfortunately. The ceiling is drywall and the roof is metal.

    I’ve had several contractors out who have given me different recommendations. One recommended tearing out all the drywall and adding spray foam insulation under the roof. Another recommended adding a return HVAC register upstairs…the problem is, there is no room in the walls for the necessary ductwork, so I would have to install one or more minisplit units. One guy just recommended buying a dehumidifier and seeing if that fixes the problem.

    Any of these courses of action is going to require a substantial investment (except the dehumidifier) so I’d like to make sure the one I choose actually fixes the problem. Do you have any recommendations for how to proceed? Or recommendations for experts to consult in my area (googling building scientists in Charleston unfortunately got me nowhere)? Do you consult remotely?


  16. Hi Ted. Hoping you can help us! We have 3 littles at home (including a newborn) and are worried with a smell in our house. We’ve have our ducks cleaned fall 2018. Our house is newly built 2015, developed bsmt. We do not have a HRV but a air ventilation system that runs in isolation from the furnace. On a timer 4x a day. On two occasions both in the evening this past month a musty stale overwhelming odor came only when the air ventilation was running not when the furnace was on. We can not determine the source and why there isn’t a smell all of the time. We have set the system to off now but still am worried it poses a health risk. Please any ideas would be appreciated

  17. Ted,
    I have a puzzle for you. On the front on my house I have a 3′ overhang with soffit venting and ridge venting at the peak. I know roof venting isn’t super important as long as your attic floor and any penetrations down into the living space are well sealed so you don’t have conditioned air and humidity leaking into the attic, which requires exhausting via soffit and ridge vents. Unfortunately, most of the general public doesn’t know this, so should I ever sell my house, appraisers and home inspectors would scream ROOF VENTING!!
    This summer I would like to add a covered porch onto the front of my house, extending the current roof line, but at a lower pitch. At some point I may screen this space in as more of a breezeway, or possibly even end up moving my living room wall out into this space to create more interior space. Either way, this space would have a ceiling at some point and be closed to the outdoor air, but I also would be enclosing the soffit venting that is in my current overhang. Due to the lower pitch I would probably like to spray foam this area, but what about the venting? Would you suggest I just extend the current venting via some sort of chase until it’s exits into the new overhang?

    As always, thanks in advance. Your insight is appreciated!

    • I’ve seen a product for exactly this type of case. Ventilating underneath the shingles on top of the roof line and into spaces like this. I’ll send you a link when I locate it.

      • Smart Vent or The Edge Vent shingle over is our solution in the midwest. There is another type that is rigid plastic and has larger openings, (Lomanco and GAF 4′ types) and we have found that on certain applications as it weathers and lifts, the vent will have enough space for the bats to get in.

  18. I bought a bungalow built in 1970 in Summerside PEI, My plan is to do a bunch of energy efficiency updates. One is building another 2×4 wall in the interior. I am using 2′ on centre and no bottom or top plate going to rabbet the 2x4s on the top and bottom to put boards at the top and bottom to avoid thermal bridging. Should I remove the existing gyproc? As well would air sealing and gyproc with primer and paint giving a Class 2 vapor barrier be acceptable?

    • This depends on your climate. What you want to avoid is that inner surface becoming cold enough for condensation formation. If your new interior insulation is much greater than the old exterior insulation, then the wall, now interior, will probably get cold enough to cause problems if you live in a cold climate and moisture gets into the inner cavity. PEI is cold enough in winter that I’d be concerned.
      If you could be 100% certain that the moisture cannot get to that wall, then you could get away with it. For example, if you framed the interior wall, then spray foamed over the interior wall and behind the new framing, you wouldn’t have the opportunity for moisture to condense on it. You could also ‘laminate’ it with sheet foam, sealing the foam around the edges and at seams. Then build your inner wall. You’d have a great thermal break and protect it from moisture.
      If it were my home, that’s the approach that I’d take.

  19. Hi Ted,
    Our single-story 1500 sq. ft. ranch home in Phoenix, Arizona was built in 1995 and has it’s original Air Conditioning system in the attic. We’re getting ready to have an HVAC company replace the 24 year old Trane electric heat pump and air handler. The ductwork is Insulated Flexible R4.2 Duct (wire reinforced with a foil/mylar appearance) and is also original (24 years old). There are about 14 supply registers in the ceiling and about half or them have noticeable dirt/dust streaks/stains coming from them. If I remove a register and run a damp finger into the dirtiest ones I get a dirty finger. We’re reluctant to have the flexible ducts cleaned for fear of damage to them. So we are debating whether to replace the entire ductwork with new flex duct. However, all 3 of the HVAC companies (who came out and gave us bids on the AC units) said new ductwork is not necessary – but, when pressed, reluctantly quoted bout $3000 for new ductwork. Only one offered professional duct cleaning instead. What are your thoughts? What is the life expectancy of this type of duct? Some websites say 10-15 years, while the Air Duct Council website says “Flexible Air Ducts should last for the life of the dwelling.” Would you replace the ducts? p.s.. We are seniors and plan to stay in the home indefinitely.

    • Air duct systems shouldn’t get overly dusty unless there are leaks in the system that permit dust to be sucked in, bypassing the air filter. OR if filters don’t filter sufficiently small particles.
      In the old days, we all used those loose fiberglass filters. They kind-of worked, but still let too much dust through. Today, higher MERV filters (MERV 8 or higher) are available which do an excellent job at filtering out very small dust particles. MERV 11 or higher will filter out things as tiny as mold spores, but you have to keep in mind that higher MERV filters resist the flow of air through the system. I personally have been happy with MERV 8 filters in my own home.
      This is a long winded way of saying that some dust around the registers isn’t unusual, but you can greatly minimize the amounts of additional dust in the future by using good filters and ensuring the new system is well sealed.
      As for cleaning – most don’t recommend it for the reasons you mention. Especially with an older flex duct which may have become brittle.
      It’s easy to tell if the ducts have become compromised over time by simply handling them. I’ve seen flex duct so brittle that it breaks with the slightest touch. I’ve also seen decades old flex that is fine. If your HVAC people are telling you that the duct is good, then you’re probably fine re-using it as long as it has been performing well over the years.

      The big thing I would suggest is ask the installers to be extra careful sealing the system for air leaks and to have a duct test performed after installation. There are tightness standard that should be met and testing is required in many areas now. Poor duct sealing will severely compromise efficiency and cause excess dust around the house.

      One other thing to have them check (or do it yourself if you’re handy) is to pull the registers off all the air supplies and returns in the house and ensure that the connection between the “boot” and the ceiling/wall/floor is sealed. Most installations are not sealed properly, allowing the passing air to suck dust in from around the boot where it meets the back of the sheetrock/ceiling/wall/floor material.

      Hope that helps. Good luck with your new installation!

  20. Ted, I have read your description of how to insulate an attic and cathedral ceiling, and many of your related blog entries. Thanks for a good resource. My builder installed T&G directly onto the rafters of the cathedral ceiling, with only a partial and imperfect vapor barrier at that. During the course of the winter when the outside gets really cold and then warms up, I get random dripping water here and there in the room, especially around the chimney, but also in some other random locations as well.

    To fix it, I will be removing all the T&G and insulation. Treat the mold that I find, then putting it back together right. To do it right, I want to put 2″ of XPS spaced 2″ from the roof deck. Then fiberglass insulation up against that. Then, to air seal it, I will staple plastic sheeting to the rafters, and put rubber tape over the staples along the length of the rafters. Finally, I will put the T&G back up, nailing through the rubber tape into the rafters for a good seal. I can send you a diagram of my strategy if you’d like to see it.

    Is this a good strategy, or am I missing something?

    • Michael, sorry to hear of your T&G ceiling issues. It is dismaying that builders continue to take the same old failed approach to constructing these types of ceilings, forcing homeowners to have to reinvent the wheel and re-do the building of their homes.
      The potential issue I can see with your solution is trapping moisture in the region filled by the fiberglass. The XPS and the plastic are slow vapor retarders, so any moisture that gets past the plastic is going to get trapped in the fiberglass without any way of getting out. A safer solution would be to place the fiberglass under the roof deck, with a gap for air flow, then put XPS under that (towards the inside of the house). Then a thinner layer (maybe 1/2″) of XPS or poly-iso foam covering everything (imagine replacing a sheet-rock ceiling with foam). This creates a durable, moisture resistant barrier.
      Then, you can put whatever aesthetic ceiling in place you’d like. The T&G could be applied directly at this point.
      With this construction, any moisture that slowly works its way up to the fiberglass layer will easily be flushed out. Moisture that passes the T&G would be mostly stopped by the thin foam layer, which will be essentially at the temperature of the inner ceiling, so condensation risk is minimal. And since there will be minimal seams between the large sheets of the thin foam, you can tape these seams for a fully continuous barrier.

      • Hi Ted,

        One other consideration here is whether the space between the roof deck and the T&G is actually ventilated. If it isn’t then this solution will create the same problem that the OP’s solution creates: the fibreglass is sandwiched between two vapour barriers (the XPS and the roof shingles) with no means of letting moisture escape.

        So for the OP, by ventilated I mean are there soffit vents and roof and/or ridge vents on the roof above your cathedral ceiling?

        Apologies for hijacking this response!


      • Good addition input, thanks Jeff.
        The risk is slightly reduced, even in an unventilated roof assembly. I wouldn’t want much moisture getting in there, but using multiple layers of foam board would reduce the moisture migration to a tiny amount. Any residual would likely be so little that it would diffuse out of the cavity through small air leaks that are likely to exist. But, as Jeff notes, best be safe and ventilate properly with continuous soffit and ridge vents.

      • Ted, I took the wood off the ceiling and noticed that the fiberglass insulation was stapled to the inside edge of the rafters, not the room-side face! No wonder I had so much moisture pouring up through. I pulled all the fiberglass insulation from the rafter bays and the undersides of the roof plywood are all blackened with mold maybe? Yes, the cavity is vented mostly by soffit vents and ridge vents in answer to Jeff’s concern. Another issue is that the insulator installed the foam spacers tight against the facia board, reducing the ability for them to vent any air. Also he didn’t vent side-ways above and below the sky-light cavities. So there is no possibility for those portions of the roof to vent. My thought is to drill some 1″ holes sideways into those cavities above and below the skylight from neighboring rafter bays.

        I have some questions which maybe you can help out.

        After I spray the blackened areas with a mold-eraser (TM), do I have to paint over it with a primer to seal the mold from the air, or once it is killed and I prevent further moisture, it won’t come back again?

        If I do as you suggest, the XPS will be right against the wood ceiling material. I read on the XPS sheet that you need a fire or thermal barrier between XPS and living space to be compliant to building codes. Is the wood layer enough of a “thermal” or “fire” barrier between the XPS and the living space, or should I put a layer of sheetrock between the wood and the XPS?

        Is the XPS really worth my effort, or will it cause more harm than good? I originally thought to add it because I wanted to increase my R value from a paltry R-30 to R-38. Still not to code, but a lot better than it was.

      • Hi Michael!

        One other option you might want to consider is bringing that ‘attic’ space (i.e. your rafter bays) into the conditioned space of your house. This requires air sealing the roof deck. This means blocking off your soffit/ridge vents (plywood with the joints sealed with acoustic sealant to provide an air seal would do the trick). You’d also want to make sure the skylight frames are air sealed as well (spray foam works).

        You can then pack the rafter bays with batts. I’d use rock wool instead of fibreglass; higher R value for rock wool, don’t deform after being wet as fibreglass batts do, plus they are friction fit into stud bays (or rafter bays in your case). If you use fibreglass, you will have to fight to hold them in place against the roof deck while you try to staple them in place… no need for your staple gun with rock wool batts!

        You could then drywall over the rafters to air seal the rafter bays from the interior then install your T&G over that.

        I would definitely not put plastic sheeting under the drywall. For starters, you’re creating the dreaded vapour barrier sandwich (shingles on one side, plastic sheeting on the other). Secondly, if you do get a roof leak, you want the water to come straight through so you can detect the leak as early as possible.

        If you’re concerned about moisture migrating through the T&G and drywall, consider that generally when moisture condenses in a wall space, it’s not migrating through the drywall, it’s entering via interior air which seeps in around electrical outlets, window frames, etc. If you air seal your rafter bays (i.e. with the drywall), you block this direct moisture infiltration. Also, by not putting plastic sheeting over the rafter faces, you are giving the opportunity for any potential moisture build up (which would be negligible) to dry to the interior on low humidity days. If you are still concerned, a layer of a vapour retarder like Tyvek beneath the drywall or even a second layer of drywall would further reduce the possibility of vapour diffusing into the rafter bays.

        Another benefit of making the space below the roof deck unvented is that you won’t need as much insulation. The large R values you see listed for attic insulation are for vented attics. The reason they are so high is because you have exterior air flowing through a vented attic, which will penetrate the top few inches of attic insulation: fibreglass, cellulose, rockwool… all of which are porous to air.

        If you do go with an XPS solution, consider that certain species of insects, particularly ants, have been known to nest in foam. If you have vented rafter bays, that’s a direct conduit for these insects to enter your attic space and find your foam boards.

        Anyway, that’s what I would do. Bear in mind that I don’t do this for a living! Building science is just a hobby of mine. I’d definitely recommend doing some research into the pros and cons of unvented attic spaces though…


    • Ted, you’re right of course that there is a minimal chance of moisture being introduced from the interior of the home through multiple layers of XPS board (in fact, I find there is a lot of fear mongering with regards to how much moisture transmission there actually is through most construction materials in most real world scenarios).

      I always side with Murphy’s Law in these situations though… for example, what if there is a roof leak? Now there is water between the roof deck and the T&G with no chance of escape. So you’re suggestion of ensuring there is a ventilated space below the roof deck is the safe bet in my opinion.

      Again, sorry for jumping into this discussion. I just found this situation an interesting one.


      • Jeff, thanks for the thoughts. However, I have read about the dangers of non-vented cathedral ceilings in a northern environment (ice dams and wood rot). So, I am going to stay with a vented design.

      • Michael, I get it. I think they can work, but it’s your house and you have to be comfortable with your solution.

        To create your vents, you can fasten lengths of 2×2 to the tops of your rafters (i.e. against the roof deck) then fasten plywood to the 2x2s to create the floor of your vent. You can then airseal the joints between the plywood and the rafters (with sprayfoam, acoustic sealant, whatever). Now you can add your batts. Instead of drywall against the rafters, maybe the 1″ of XPS that you both were talking about is a better choice… much lower permeance than drywall (and at 1″ thickness, not quite a vapour barrier, which is what you want), which will go even further to minimise moisture diffusion into your ‘attic’ space. Then your T&G on top of that.

        Whatever you do, I think the most important step is to airseal the insulated segment of your rafter bays.

        Anyway, good luck with your project!

      • Jeff, I am wondering if I need anything between the living space and the XPS foam for fire protection, besides the wood ceiling material. The XPS material from Corning said that I need a fire or thermal barrier, depending on the local codes. Is the wood enough of a fire or thermal barrier, or do I need a layer of gypsum between the XPS and wood T&G?

      • The other question is, I already have a full vapor barrier on the room side of the rafters. Why do I need to worry about sealing the roof side? Shouldn’t I leave that open to moisture so it doesn’t trapped in the insulation layer? We just want to stop wind from interacting with the fiberglass insulation, because that would reduce its effectiveness as an insulation, but we are not trying to stop the moisture flow, right? If so, the air-gap channel should be made of something that prevents air-flow, but not moisture. Could I staple a layer of cardboard to the 2×2’s that you suggested, instead of plywood. Plywood seems to be a little overkill, and the foam sealant on the edges might be appropriate for moisture sealing which is not necessary, I think. What are your thoughts about that?

      • In my part of the world, 1/2″ gypsum or 5/8″ plywood are generally accepted as sufficient thermal barriers. Your building code may vary, but I suspect not.

        The vents under your roof deck are exposed to outside air/humidity/insects. I wouldn’t put any cardboard in there! The plywood would not be blocking moisture at all; 1/2″ plywood is considered a vapour semi-permeable material, so a vapour retarder, not a vapour barrier. The plywood would be acting as a vapour retarder and air barrier. As well, plywood is sturdy enough to resist any bulk water (as in from a roof leak) and to keep insects out of your insulated attic space.

        Sealing the edges of the plywood with sealant or foam would serve to air seal the attic space; you don’t want any air from the roof deck vents or from the interior of the house to enter your insulated attic space. Air infiltration is the prime culprit in introducing moisture into a space.

        So to summarise: you want zero air infiltration into your attic space. You do not want to enclose the attic space with vapour barriers. It’s key that moisture be allowed to escape through vapour permeable materials (and again, not through air gaps!).

  21. I am trying to figure out if I have mold between hardwood floor and subfloor. Old house with dark floors. What can I do?

    • Unless the floors have been allowed to remain wet, there’s little reason to suspect that they’re moldy. Does the floor feel “squishy” like it’s rotting? Are there any other symptoms besides some discoloration? Wood will naturally discolor from water damage such as under flower pots or repeated animal urination on carpets (trapping the moisture between the carpet and floor).
      If you have significant reason to suspect mold issues, you might have to have someone remove the hardwood floor in the damaged area so they can examine the wood below. However, this is a fairly drastic solution that requires cutting and prying out the boards and should only be done as a last resort

  22. Ted,
    I’m very aware of your disdain for recessed cans due to their flawed characteristic of having a 5-6″ infiltration area into your attic space and unconditioned air. Would you still dislike them as much if I built a box out of insulation board to enclose them in the attic? I know they have the LED retrofits for existing cans now which may help with cutting down on air infiltration, but honestly, I’m not a big fan of the hue of LEDs yet.

    Much thanks!

    • I’ve built boxes in the attic for my pre-existing recessed lights, so it’s certainly a feasible solution.
      However, it was a real pain due to the hardware on the attic side that got in the way of the boxes, requiring me to notch the boxes and fit them into awkward spaces. I made mine out of foil-faced poly-iso board. Foil tape sticks to this very well making construction relatively easy.

  23. Ted,
    Our home is in the Phoenix area and we have 12 interior soffits, with the kitchen being the largest at 18′ x 17′ x 18″ depth none of which has insulation. Should we consider blowing insulation into those soffits or air sealing the attic floor over those soffits with a material such as Astrofoil?

    • I would definitely air-seal the attic floor above them. My personal preference would be to use 2″ thick poly-iso foam board, caulked in place to air seal the areas and then add insulation on top of that to help reduce the heat that will be trying to invade from those hot Phoenix summers.

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