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burnt03 11-09-2012 10:51 PM

Sealing crawl space rim joists and walls
Talked to the local building inspector, he noted that our code says to put batt insulation into rim joist, then rigid polystyrene (sealed around perimeter with spray foam or caulk) on next.

Couple things:

1) Don't have a sill plate, the floor joists are resting directly on the concrete foundation wall. Should I put the rigid in flush with the inside of the concrete wall?

2) Foundation wall currently has 2" white foam (EPS?) insulation which I don't think acts as a moisture barrier. Crawl space has plastic on ground, was going to fasten it to the walls at the same time. If the EPS isn't a moisture barrier, should I be bringing the plastic up the walls and fastening to the bottom of the rim joists?


Windows on Wash 11-10-2012 07:08 AM

EPS works okay as a bulk moisture barrier. Hopefully they did a good job waterproofing it to outside.

I wouldn't run the plastic all the way up the wall. Its intended purpose is not to trap the bulk moisture in and you would be hiding it where you can't see it.

You will want to know if you have water coming through the wall as compared to trapping it under the vapor barrier.

I would put the rigid tight to the outside wall, seal it up, then cover with a batt for fire protection.

burnt03 11-11-2012 08:59 AM

Took a closer look at the insulation, looks like it might be styrofoam?

If so, does it work as a vapor retarder?

Windows on Wash 11-11-2012 10:14 AM

Its EPS.

It does work as a vapor retarder but it is more vapor open than XPS depend on skins.

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