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What should I do before I put in attic floor?

Matthew Fleck | Posted in General Questions on

Hi all,

im in the process of creating a livable space in my cathedral attic. I’ve done a lot of insulating work on the roof and dormers, and now I’m shifting to the attic floor. Currently there’s a rough subfloor down original to the house. It’s 3/4 pine slats with some healthy gaps between them nailed into 3×8 joists. I’m planning on laying a plywood subfloor and then finishing with wide plank flooring. 

Im planning to pull up a few floor boards so I can air seal around some light fixtures in the ceiling of the floor below. But other than this, I’m not sure what else I’d want to do in there. Is there anything else that you’d recommend I do before I lose easy access to this space?


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  1. Jonathan Blaney | | #1

    Is the structure adequate for use as a living space. Why the plywood? Is it just underlayment? Have you considered future electrical needs? What is your heating/cooling plan?

  2. Matthew Fleck | | #2


    There are several homes like mine in our neighborhood and I know that several have refinished attic. It should be structurally viable.

    I’m 50 50 on the plywood. The subfloor is pretty rough and not to even. I may skip the plywood and lay the flooring directly on the existing subfloor.

    I’ve already run a few electrical lines up for outlets and lighting.

    I’m planning on putting in mini splits with a single head for the full/open space.

    Anything I should do in that space from an insulating perspective (though I’m open to all advice otherwise!)?


  3. Expert Member
    Zephyr7 | | #3

    Are you SURE your attic is structurally sound for this purpose? You don’t sound sure, and just because other homes seem ok doesn’t mean that they are, or that yours will be. Safety of the structure for the intended purpose is not a place for guesswork. If you don’t have the experience to be able to evaluate this yourself, contract someone who does (like a qualified engineer).

    You don’t generally need to air seal between levels unless you’re planning on only using the attic as conditioned space occasionally. You DO need to air seal and insulate the outlet perimeter though, which includes the roof. You MIGHT be a candidate for spray foam here, but you might also have other options depending mainly on the depth of your rafters.

    I don’t see any problem with laying some plywood over the slats. It used to be common to build floors that way before everything went over to T and G plywood and OSB. You’ll end up with a very solid floor.

    Make sure you run enough wire for EVERYTHING you might want up there. That might include some coaxial cable or network cable for home theater or a computer, for example.


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