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Insulating a tongue-and-groove ceiling

bfDXYQ7H3g | Posted in Energy Efficiency and Durability on


How should I air seal and insulate a pine tongue-and-groove ceiling?

My house has a T&G ceiling. Over time the boards have contracted and caused gaps at the tongues and grooves. In a few areas where the ceiling has an angle change, I can see the insulation’s kraft paper.

When the boards were installed, nothing, such as sheetrock, was installed prior to installing the ceiling boards. Kraft-faced fiberglass insulation is installed. Right or wrong, the paper wings on the batt insulation was stapled inside the rafters instead of being overlapped and face nailed to the rafter ends.

Pulling down all the boards and installing material to air seal the ceiling is not an option.

How could I air seal the ceiling from the attic side? Spray foam is also not an option since the foam could expand through the T&G gaps and be seen.

Thank you.

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  1. GBA Editor
    Martin Holladay | | #1

    Your ceiling has no air barrier, and it needs one. If you want to do the work from the top side, remove and discard the fiberglass batts. Install strips of rosin paper, cardboard, or rigid foam between the ceiling joists to limit the amount of spray foam that will ooze between the boards. Then install at least 2 inches of closed-cell spray foam in the joist bays. The installer needs to pay careful attention to be sure a good air seal is effected, from joist to joist.

    Then install 12 to 20 inches of cellulose.

    If you want to work from below, leave the existing ceiling in place. Install gypsum wallboard and tape the seams. If you like to look at pine boards, you can install a new pine board ceiling if you want, as long as the drywall is in place.

    No matter which of the two approaches you take, don't forget to seal around electrical boxes and other penetrations, and make sure that your access hatch is equipped with weatherstripping.

  2. bfDXYQ7H3g | | #2


    Thanks for the help.

    Your recommendation is close to what I thought of doing. What about installing glass-fiber-reinforced polyisocyanurate foil faced foam board (Dow Thermax) instead of blue/pink foam board between the rafters? The foam board edges where it meets the rafters could be spray foamed to air seal. Blown insulation could be used to cover the foam board.

    I do like the solid spray foam idea but not sure I could find a quality company to do the job where I live.

    I know I'm loosing heat through all the gaps but I want to be sure I have a good plan before I start. Don't want to fix one problem and have that cause another.

  3. GBA Editor
    Martin Holladay | | #3

    Your plan will work, although it is difficult to get a really good air seal with just rigid foam, even if the perimeter of each piece of foam is sealed with canned spray foam.

    The problem is that over time, the joists will move -- due to changes in humidity, changes in temperature, loading (if the attic is used for storage), or ordinary vibrations (door slamming, trucks driving by, etc.) If you can find someone to install 2 inches or more of closed-cell spray foam, you'll end up with a better job.


    I have to confess that I once had to pull down a T&G ceiling and re-install it. I was very happily surprised at how quickly and easily the ceiling came down with very little damage and likewise how quickly it went back up. Most of the hails stayed in the framing and just pulled through the backs of the tongues with very little splitting. the few nails that did come away with the ceiling wood were pulled through before we stacked the wood for re-install.

    I know you have said that taking the ceiling down is not an option but I haven't heard the reason for that statement, it seems that pulling it down, adding taped foil faced poly-iso foam or drywall and then running 1x3's and re-installing the ceiling would be pretty straightforward.

  5. wjrobinson | | #5

    I also recommend as Michael Chandler has. It is not days of work, more like two to three days depending on your particular build to pull and reinstall T&G. (The building codes should require drywall or better ridgid foam under T&G.)

  6. bfDXYQ7H3g | | #6


    Understand your point on joist movement. I'll do some checking for spray foam companies.


    I've never removed and installed T&G. I do wish the ceiling had been installed correctly at construction in 1992. Maybe there were no building codes in N.C. in 1990's (not 1890's).

    We are living in the house. Also, there is over 900 sf of T&G ceiling that is stained. Some is sloped up to a loft. Even if I removed and re-installed correctly I suspect I would be short on boards since the re-install would close the existing gaps. No problem if the boards were painted. I could never match the stain color on the new boards.

    Why the 1x3's? Air gap between the boards and insulating board? Is there a problem installing the T&G directly against the foam board? If so, would I need this gap if I do the work from the attic side?


    Maybe no one looked at the ceiling installation. Sure is causing me a headache.

    Thanks for the continued help.

  7. wjrobinson | | #7

    Walter, stain can be matched. I have done so. A bit of testing on scraps and anyone can do it. Your idea of going in from the top for me is a much more of a project and I think Martin had a sound way though expensive!

    Realisticly... Leave it the way it is. Or pull the boards, or sell the problem. Imo...

  8. bfDXYQ7H3g | | #8


    Ok, thank you for the stain suggestion.

    If I were to go with foam board, can the foam board (foil faced or not) be placed directly against the attic side of the T&G boards? Or should there be a 1 inch air gap between the T&G board and the foam board? I'm looking for a spray foam company to top the foam board.

    Thanks for the help.

  9. wjrobinson | | #9

    Tight to T&G Walter.

  10. GBA Editor
    Martin Holladay | | #10

    Directly against the T&G boards is the way to go.

  11. bfDXYQ7H3g | | #11

    Ok, no gap.

    One other issue, the existing insulation. It's kraft faced fiberglass batt. I would rather not dispose of it. With foam board installed, is the kraft face still needed as the vapor barrier or can it be peeled off the batt and the now un-faced batts reinstalled in the joist bays?

    I do like the blown-in insulation suggestion but would like to re-use the batt insulation. Maybe I'll top the batts with blown-in for a higher R value.


  12. Expert Member
    Michael Maines | | #12

    Walter, are you picturing the batts between the rigid foam and the roof sheathing, or between the rigid foam and the T&G interior boards? Either location is acceptable, and the kraft facing could stay on in either case, but the batts might perform better if the foam was toward the outside and the batts toward the inside.

  13. bfDXYQ7H3g | | #13

    Actually, insulating batt or blown-in insulation will be above the foam board which will be above the T&G boards. Foam board will be the air seal for the ceiling.

    Here is a drawing:

  14. GBA Editor
    Martin Holladay | | #14

    You can reuse the fiberglass batts if you want. But you'll get better performance if you throw them away and install a nice, clean new layer of cellulose on top of the foam board.

  15. bfDXYQ7H3g | | #15

    Thanks Martin. I'll do some checking for cellulose contractors in the area.

    I appreciate everyones help with my questions.



  16. wjrobinson | | #16

    Walter have you put together cost estimates for each option? Am thinking not pulling the boards is many times more expensive. Let us know if you would.

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