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Best way to insulate raised floor over crawlspace

wisjim | Posted in Energy Efficiency and Durability on

This doesn’t seem to exactly correlate with any previous questions that I have found, but feel free to direct me to previous answers I may not have found myself.
We have a sunroom that we built to replace a failing porch about 25 years ago. It has a block foundation and slab floor and is attached to the house at one side. The block and floor have 1″ styrofoam insulation on the outside. The floor is now 4 risers down from the adjoining room (and the level of the rest of the main floor.) The steps down into the sunroom take up a lot of room, and my aging knees and hip make it uncomfortable for me to use these steps, so the room isn’t used much anymore. Our plan is to raise the floor level in the sunroom with new joists and end up with a new tiled floor at a higher level.

My principle question is about the best way to insulate the new raised floor. Using fiberglass batts between the new joists doesn’t appeal to me, so we are thinking of putting a subfloor over the joists, then 2″ of foam, then cement board and finally ceramic or quarry tile. I’m not sure if another layer of subfloor would be needed between the cement board and the foam. Any suggestions or other methods to use?

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  1. GBA Editor
    Martin Holladay | | #1

    There have been several Q&A threads on this topic (which I might call "creating a crawl space that isn't high enough for a human to enter").

    My own preference is to pour a new slab over a very thick layer of rigid foam. If the rigid foam gets too expensive, you can use sand or crushed stone as fill -- followed by thick rigid foam and a new slab.

  2. wisjim | | #2

    I thought I would update my project. We need to raise the floor about 20 to 22 inches. A friend who is remodeling his house and who checks out Craigs List and other sources frequently, found a lot of 4" foam insulation at a really good price, so we bought enough to fill our space to a depth of 20 inches. It will then have a new floor placed over it, and we should be all set with a much more usable space. We are thinking of using linoleum tiles for the new floor covering.

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