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Is Drywall Required Under Tongue-and-Groove Ceiling Between Two Living Spaces

arnoldk | Posted in General Questions on


My wife really wants to do tongue & groove ceiling for the main living area on the first floor but it may be cost prohibited, at least initially. The reason is because I was under the impression that drywall was required under neither the tongue & groove for fire rating purposes but I cannot find anything indicating that. Does anyone know?

I live in Ottawa, Ontario, Canada.

Thank you,

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  1. Expert Member
    BILL WICHERS | | #1

    The fire rating requirement typically comes into play if you have insulation in your ceiling that requires a thermal barrier which is what the drywall provides in this case. Spray foam requires this, mineral wool (among others) does not, just as two examples -- that's not an exhaustive list.

    You will most likely need an air barrier though, which drywall provides but there are other ways to do it too. Sometimes 1/2" polyiso is used with seams taped, sometimes plywood. You just need something that can be air sealed, even housewrap has ocassionally been used.

    You might need a vapor barrier too per your local code. We have some others on here that are Canadian builders who will know.


  2. Expert Member


    I'm a bit unclear as to whether the ceiling has another floor over it, or a roof, so I'll answer both ways.

    There is no requirement for a rated fire separation between the house and either the floor above, or an attic or roof, and the flame-spread rating of wood is under that allowed for finished surfaces, so you are good to go.

    There is however, as Bill said, a requirement for a vapour and air barrier if there is a roof or attic above. That can be satisfied by a few materials: Drywall, plywood, or OSB with a vapour-barrier paint all comply. You can also use 6 mil poly. What I'd call the "house" position on using poly under t&g here on GBA is it's too fragile, but using it is fairly common here in Canada under wood ceilings, and it seems to work.

  3. Expert Member
    BILL WICHERS | | #3

    Malcolm noticed something that I didn't so I want to clarify my first post: I had assumed this ceiling was below an attic, or was a cathedral ceiling. If this is just a ceiling with a floor of a second level above it, then you can put your T and G up directly with no issues.

    Fire rated materials are usually required when seperating livings spaces from combustible materials (such as spray foam, basically things that are easier to ignite than wood), or from higher-risk locations (like attached garages). "Regular" walls, floors, and ceilings that just divide different interior locations within a home don't have these fire rating requirements.


  4. aaronbeckworth | | #4


    Assuming living space above the floor, would it be best practice to install drywall above the T&G for sound dampening? And if batts, such as Safe’n’sound, we’re installed in the joist bays would that change your answer?

  5. Expert Member
    BILL WICHERS | | #5

    Drywall will help with some types of sound, like people talking or a radio playing, but it won't help much with footfalls and people walking around. If you want to get the most bang for your buck, 5/8" type X drywall and safe and sound mineral wool will help, and stop most normal talking from being heard. If you want to stop hearing people walk around, the best things you can do are to hang your ceiling drywall on hat channel and/or use carpeting on the upper level, both of which are a pretty big step up in cost and complexity from the drywall+sound insulation.


  6. walta100 | | #6

    Generally no code requirement but if this is a cathedral ceiling you need an air barrier that the tongue and groove will not provide. This will keep the warm moist air in your house and out of your insulation. Without the drywall you are very likely to be back asking “how to fix my moldy rotting cathedral ceiling”. I can’t remember the last time we went 2 week without someone asking.

    Cost prohibited ??? Drywall may well be the least costly building material in your home by the pound and or the square foot. If you will be covering the drywall make sure the finishers know to stop after the second coat.


    1. Expert Member
      MALCOLM TAYLOR | | #7

      There are no code requirement that I know of in Canada, but I recall a recent discussion here that the IRC requires drywall to protect I-joists or dimensional lumber smaller an 2"x10"s in certain situations.

      1. bcade | | #8

        Came here to mention the engineered floor framing caveat, that's all I came across when looking to do something similar. APA has a pretty solid page for reference,

    2. PBP1 | | #9

      Good info, possible clarification? For unvented, flash-n-batt (with sufficiently thick closed-cell spray foam), I believe a vapor barrier is not recommended (to be avoided). With thick closed-cell SF (> R-25), the dew point temp is likely to be well within that layer to reduce risk of condensation on the surface/wetting of the batts. For large spans (20 ft or more), structural engineers may ask (a) tng or (b) drywall. If (b) drywall, then you may need larger beams/more beams to assure less movement such that the drywall does not crack; whereas, (a) tng is forgiving unless it's installed with the wrong moisture content such that shrinking/swelling occurs, which can cause substantial gaps due to shrinking or puckering due to expansion. Care should be taken with tng to make sure it is at the "right" moisture content and, if painted/stained/etc., that should be taken into account as well (common sense as with flooring).

    3. arnoldk | | #11

      Hi Walta,

      The location of the t&g pine will be on the first floor of a two story house. I understand that drywall is relatively cheap but things cost a lot more in Canada and with the recent increase in some building material, mainly wood and steel. I am trying to keep things on budget since we have been saving for ten years to make this happen given we don't have the big salaries.

      Thank you,

  7. arnoldk | | #10


    Sorry for the late response. I was at the property most of the weekend clearing more trees for the house.
    To clarify, the house is a two store rectangle (30' x 40') and the t&g pine would only be install on the first floor in the entrance, living room and dinner area. There are no cathedral ceiling in the house I attached a copy of the floor plan for those who want a better idea.

    Thank you,

  8. walta100 | | #12

    I think you have a fabulous plan.

    Would you consider losing the bump out and simplifying the roof line while keeping the square footage the same by extending the width? Every corner adds surface area per sqf. Extra corner take extra time to trim. Unless the house backs up to a lake why spend money adding interest to the back of the house?

    Consider flipping the bathtub around to keep the plumbing out of the exterior walls.

    Consider flopping the master closet and bath to shorten your plumbing runs.

    No need I can see for drywall above a first floor T&G ceiling


    1. Expert Member
      MALCOLM TAYLOR | | #13

      "No need I can see for drywall above a first floor T&G ceiling"

      Beyond sound attenuation.

  9. dk_reno | | #14

    I need similar advice for Bunkie on top of garage that is detached from the primary house . It’s spray foam and I plan to put t&g pine . Do I need drywall ?

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