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Community and Q&A

Remodel with raised floor: insulation options?

Brian Lueking | Posted in Energy Efficiency and Durability on

we recently began a renovation and I am hoping to get some guidance on best practices for insulating under our floor. We added a new attached garage and are renovating the old attached garage into interior space. The old garage was two steps down from our home and we will be adding I joists across the area to bring the renovated space onto the same level as the rest of the house. We live in climate zone 6 and the old garage floor is 4″ concrete with good drainage but no poly under. With the i joists there will be a space of approximately 10″ from the bottom of the i joists to the top of the concrete floor.

My plan was to treat this space as an unvented crawl space. I was going to put poly over the concrete and wrap it up the 8″ concrete stem walls and tape all the seams. I would then add 4″ of EPS foam to the perimeter of the concrete walls sealing any seams or gaps with canned spray foam. The main question I have been unable to find an answer to is if it would be beneficial at all to insulate above the old concrete floor in this unvented assembly? My though was to continue the 4″ of EPS across the floor as well then maybe filling the rest of the space with blown in cellulose. I would think the floor foam would be beneficial but I am not sure if adding the cellulose would be beneficial at all or if it would add unforeseen issues. This crawl space area would have some plumbing and heating vents but would basically be inaccessible after construction was completed.

Thank you for your time I have greatly enjoyed reading this site and these forums and look forward to continuing to improve my homes energy efficiency as I tackle our renovations.

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  1. Expert Member
    Armando Cobo | | #1

    I designed the same type of remodel to an existing house in CZ3 in TX about 2 years a go. The garage floor to house floor distance was 24", so we installed the moisture barrier, then 2" of sealed polyiso on floor and walls, 14" floor trusses (for ducts, plumbing and electrical), and filled the cavity with cellulose. Overkill, but the homeowner wanted to make sure the had warm toes.

  2. GBA Editor
    Martin Holladay | | #2

    As far as I know, most building codes require that a crawl space be high enough to allow human access. I don't think that inaccessible crawl spaces are legal.

    I think that the best solution is to fill the space with EPS foam (or a combination of crushed stone and EPS foam), followed by a 4-inch concrete slab.

    Thick EPS foam can be ordered from companies that specialize in EPS foam.

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