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How to attach rigid insulation to crawl space floor

Keith92705 | Posted in General Questions on

I am located in Zone 3B, Orange County Ca.

I am going to seal my crawl space and insulate the walls with rigid insulation. Here is the code from the CEC Residential Compliance Manual:

“Insulation: The R-value of insulation placed on the foundation stem wall shall be

equal to or greater than the wall insulation above the raised floor. Stem wall

insulation shall run vertically along the stem wall and horizontally across the

crawlspace floor for a distance of 2 feet (24 inches).”

What is the best way to attach the rigid to the ground (and seal the 90 degree joint)? I did not want to use batt insulation in this application, but based on this requirement, it seems better suited to this condition.

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, you may want to read this article: Building an Unvented Crawl Space.

    You don't want to install any fiberglass batts in a crawl space. If you end up installing any insulation on the crawl space floor, you should either use EPS or XPS. EPS is more environmentally friendly than XPS.

    Details depend somewhat on whether your floor consists of dirt, crushed stone, or a slab.

    If you have a slab, the insulation can be fastened to the slab with TapCon screws and fender washers.

    If you have a dirt floor or a crushed-stone floor, you need to cover the surface with polyethylene. Then if you install any rigid foam insulation on the floor, you can hold it in place with bricks.

    Most building codes require that rigid foam be protected by a layer of 1/2" drywall or cement backerboard. You should check with your local code officials before proceeding.

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