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Air seal a tongue-and-groove ceiling?

user-964026 | Posted in Energy Efficiency and Durability on

Located in the hot/dry climate of Central Ca. How do we air/seal a combination roof/ceiling with tongue and groove ceiling? The roof is cement tile and the insulation is R-30 fibreglass batts. The home owner does not wish to remove the roof but might consider it if the solution is less expensive and a much better alternative to correction from within.
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  1. YYH8rX5BRv | | #1

    It's too labor intensive to calk and it will not hold for a long time. There is no good option other than redo or overlay
    Daniel Glickman.
    Sustainable Construction Services

  2. davidmeiland | | #2

    I've got a similar situation at a job. I'll be interested to hear what others say. One thing that has occurred to me is injection foam installed from the eaves (screened vents could be opened), and I may have the installer out to look at the situation.

    Since you have a concrete tile roof you could remove and replace tiles, a lot different than stripping a roof to do insulation.

  3. GBA Editor
    Martin Holladay | | #3

    There are only two options -- working from the inside (new drywall ceiling, followed if desired by a new T&G ceiling) or working from the outside (stripping everything and installing spray polyurethane foam from above).

    I'm fairly sure that working from the inside is going to be less expensive.

  4. user-964026 | | #4

    I like the idea of working from below as Martin suggested but wit sheetrock against the existing tongue and grove considering the building is 20 years old and the wood has shrunk exaserbating the air leaks I am concerned the normal roof venting thru the roof assembly will carry moisture that may settle on the sheet rock (wet to Dry) and with no direct air flow cause mold to grow especially in the winter when the air flow thru the roof assembly is greatest and tends to be moist. We do have fog in the winter.
    What is your opinion of installing firring strips on the underside of the ceiling, covering with high density foam board then new tongue and grove over the foam board which has provided additional insulation properties of the ceiling?

  5. GBA Editor
    Martin Holladay | | #5

    In cases where condensation occurs on roof sheathing above a cathedral ceiling, the source of the moisture is interior air, not exterior air. During the winter, exterior air is dryer than interior air. If there is condensation on the sheathing, it means you have no air barrier, and interior air is leaking into the ceiling assembly. Ventilation through the soffit will not lead to condensation.

    Your proposal to install foam sheathing will work, as long as you can find a way to ensure that the foam layer is airtight. That requires careful sealing of the rigid foam seams, using canned foam or high quality tape.

    Some experts worry that foam can shrink over time, however, reducing its effectiveness as an air barrier. Drywall is safer than T&G boards as your final finish ceiling -- because drywall is airtight.

  6. user-964026 | | #6

    Thanks Martin, We will be removing portions of the existing sheathing at the ridge to inspect for damage.

  7. davidmeiland | | #7

    Adam, in your case I doubt you need to remove the T&G. It's being recommended in other cases because the T&G is installed on cathedral ceilings and there's no way to get at the back of it except by removing the roof. In your house I would go up in the attic, get the fiberglass out of the way, cut pieces of thin plywood, rigid foam insulation, or drywall, and install them on the top of the T&G, with caulk or canned foam at all edges, gaps, etc. It might not be quite as good as continuous taped drywall but it seems greener than removing (and trashing in the process) the T&G. You are trying to create an air barrier, so a blower door is going to be helpful in doing this job. Once that's installed, put back loose fill cellulose, or maybe the fiberglass.

  8. bzockoff | | #8

    I have another similar problem situation. An 18-25ft. high T&G ceiling which is very ornate and the client is unwilling to have it removed. It has NO wallboard backing but foil faced R30 fiberglass which has extensive air leakage. The wind washing up the rafters from the continious soffit vents is a major problem. I'm bidding roof removal and foam insulation. Can it be sprayed onto the T&G ceiling with a plastic vapor barrier? Add fiberglass batt over it to fill most of the 12" bay then replace the soffit venting and ridge vent?

  9. davidmeiland | | #9

    If you are removing the roof, I would either install rigid foam or spray foam to the back of the T&G. Do you have easy access to someone to spray 2# foam?

  10. szzcDRab7k | | #10

    I have a similar situation, however with a regular ventilated attic and in a different climate zone. This is a mountain lodge in the cascade mountains in the pacific northwest, at 4,000 feet elevation. The flat ceiling is tongue and groove with a well ventilated attic and R-30 fiberglass batts.
    Is the only solution to remove the tongue and groove, install drywall, and then re-install the tongue and groove? Or would it be ok to remove the fiberglass batts, install a tyvek air barrier, and then reinstall insulation on top of that? Spray foam is another option but it would be more expensive, and I would worry about it leaking through the tongue and groove to the inside and looking like crap.

    I'm also interested in best practices for tongue and groove knee walls. Put up a tyvek air barrier behind it to air seal? Or remove and rebuild with drywall?

  11. szzcDRab7k | | #11

    Thanks David for your helpful ideas. I think a plastic vapor barrier would be a bad idea in any of these cases since moisture could get trapped in there between the plastic and the tongue and groove and on the cold side of the wall. Tyvek would be more forgiving. But I agree that the best idea to create an air barrier would be to install a layer of drywall, plywood, or foam board to the back of the tongue and groove and air seal it in place. Tyvek or some other brand of vapor permeable air barrier could be installed on the cold side of the insulation as an additional air barrier. But a plastic vapor barrier could cause problems.

  12. kelly_coons | | #12

    So I know this is a pretty old article but hopefully someone is still out there tuning in.
    I have a potential client (friend) that came to me seeking an answer to a similar problem except for his issue is in the summer. Last year they did a re-roof (tore off shake which was over sheathing and replaced with comp) and he started seeing condensation at the top of his T&G wood ceiling. They did a bunch of air sealing, addressed moisture/humidity issues and thought they had the problem fixed. First hot sunny day this year and it started showing up again. He pulled the ridge cap off and found it to be pretty wet. Why he was in there he got some good pictures of the construction and it is essentially made up of 2" T&G ceiling over 4x rafter beams, a plastic vapor barrier, 2x4 sleepers on edge with 3 layers of 1" ISOPOLY or what appears to be. Then roof sheathing. So in my experience I would say he has an air loss issue through the T&G, a vapor barrier issue as the compromised vapor barrier isn't really doing anything and a serious lack of insulation. I think the shake allowed it to breath just enough to allow for the moist air to escape. The home is in climate zone 5, colder winters and hot sunny summers. They don't want to loose the ceiling so my planned fix would be to take off the roof and sheathing, pull out the old vapor barrier and insulation, fill the 2x4 cavity with closed cell spray foam (vapor barrier, air seal and part insulation all in one), scrape that flat and then overlay with enough rigid insulation to meet R-50 and then sheet and re-roof. If I can find the CI panel that would get us to the R-25 I would use those as I assume to hit about R-25 with the spray foam. Am I heading in the right direction? I sure don't want to propose something that won't work. We also discussed replacing the 2x4 sleepers with 2x10 and doing the spray foam for 2", then rigid, then air space for venting? Any input would be great.


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