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Community and Q&A

Carport attic

howard_road | Posted in Energy Efficiency and Durability on

I have a new two car Carport that was constructed with Attic Trusses. The Attic Space is unheated and uninsulated. It’s just going to be storage space for the time being. However, in the future I would not rule out converting it to living space. I have already installed the plywood subfloor in the Attic, but not the 1×6 Pine T&G ceiling in the Carport. (Attached drawing incorrectly shows a plywood ceiling)

I’m looking for insulation suggestions for the Attic Floor/ Carport Ceiling Assembly.

What would you do now as a minimum before the ceiling goes up?
How would you add R Value at a later date if converting to Living Space?

Thank you

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  1. GBA Editor
    Martin Holladay | | #1

    It's impossible to answer any insulation questions if we don't know your climate zone or geographical location.

    In general, it's not a good idea to install a tongue-and-groove pine ceiling (which leaks air like a sieve) unless you first install a layer of gypsum drywall as an air barrier. The drywall should be taped before you begin installing any tongue-and-groove boards.

    For more information on insulating this type of floor -- one with outdoor air under the floor -- see this article: How to Insulate a Cold Floor.

  2. howard_road | | #2

    Hello Martin,

    Two additional pieces of information...
    House is located in Detroit Michigan.
    Bottom Cord of the Attic Trusses are 2x10s

    I have been working under the assumption that the T&G ceiling is not going to be my air barrier.

    What do you think about installing a layer of taped rigid insulation to the underside of the Joists? Better than drywall? Then later (if a conversion is to take place) blown in cellulose could fill the floor cavities.

  3. GBA Editor
    Martin Holladay | | #3

    It's good that you realize that tongue-and-groove boards aren't an air barrier.

    If you eventually fill the joist bays with cellulose, then you need two air barriers -- one above the cellulose (probably plywood subflooring) and one below the cellulose. The air barrier below the cellulose could be rigid foam with taped seams, as long as the rigid foam is installed with attention to air sealing.

    Most garage ceilings are required by code to be protected with 5/8-inch drywall (for fire safety). I'm not sure what your local code requirements are for a carport, by drywall is probably a good idea. In any case, you need to install something on the underside of the rigid foam for fire safety, so I would use drywall.

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