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Underslab insulation detail at perimeter

Last Post 23 Apr 2010 07:53 PM by Randy Navarro. 6 Replies.

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Randy Navarro User is Offline

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Posts:3

20 Apr 2010 11:25 PM
Hi all. I'm gearing up to begin an addition on my home here in the Pacific Northwest--specifically Kenmore-about 20 minutes north of Seattle. I suppose I'll be hanging out here more frequently and contributing whatever I can offer. I've searched the forum but haven't been able to find what I'm looking for. I'm installing radiant tubing under slab. Standard install--2" EPS foam under entire slab etc. Is there is a best practice detail for terminating that foam at the perimeter? I'll be pourind a standard 16" footing with 8" stem wall, then in-filling with the slab. Or. . . I'm open to other perimeter foundation details if I can maximize the insulation detail with another method.

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New Member

Posts:88

22 Apr 2010 07:49 AM
If you are using the slab as your finished floor, place foam on the outside of the stem wall and run it up an additional 4" and then pour up to that. Your inside foam in this scenario should touch the inside of your stem wall. You should also give consideration to insulating ( with foam) both sides of your stem wall ..if you haven't already.

arkie6

Veteran Member

Posts:1453

22 Apr 2010 10:32 AM
ICF would be a good option for your stem wall. This gives you the insulation around the perimeter. If your stem wall isn't too tall, you can pour the footing and stem wall using ICF at one time. Here are a couple of options for an ICF stem wall and footing monopour: http://www.fab-form.com/products/fastfoot/monopour.html

Randy Navarro User is Offline

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Posts:3

23 Apr 2010 11:45 AM
Thanks for the replies. I'm hesitant to drop any foam on the outside of the stem wall here the PNW. As a home inspector, I've seen too many carpenter ants tunnel right through the foam--especially the XPS (white beads.) I probably don't have too many options other than the traditional: 2" EPS on the inside of the stem wall flush with the top of the stem wall (or beveled at the top) and then pour the slab. Open to other ideas still . . . Scratchin' my head over foam. . .

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Dana1

Senior Member

Posts:6991

23 Apr 2010 12:21 PM
Posted By Randy Navarro on 23 Apr 2010 11:45 AM Thanks for the replies. I'm hesitant to drop any foam on the outside of the stem wall here the PNW. As a home inspector, I've seen too many carpenter ants tunnel right through the foam--especially the XPS (white beads.) I probably don't have too many options other than the traditional: 2" EPS on the inside of the stem wall flush with the top of the stem wall (or beveled at the top) and then pour the slab. Open to other ideas still . . . Scratchin' my head over foam. . . Borate loaded EPS (eg Performgard) pretty resistant to ants & termites, even in below-grade applications, if that's a real concern. BTW: XPS is never white beads, EPS is. Both are good for under-slab insulation, but XPS is more vapor retardent, and has a ~25% higher R value for any given thickness. EPS is usually cheaper per unit-R.

arkie6

Veteran Member

Posts:1453

23 Apr 2010 06:03 PM
Another option if you are concerned with ants, termites, or whatever in the foam is to install thin galvanized flashing over the top of the concrete and outside foam to act as a pest barrier. You can also get or make taper top ICF forms so that the concrete essentially flows to the outside edge of the foam at the very top (good idea for wall load bearing anyway). Combine this with a wet set light gauge galvanized angle ~3" x 3" over the outer foam and you have an effective barrier. Now the termites and ants might still burrow in the exterior foam, but I would think the net effect of any damage they might do would be nil. And a perimeter insecticide treatment should address that.

Randy Navarro User is Offline

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Posts:3

23 Apr 2010 07:53 PM
BTW: XPS is never white beads, EPS is. Both are good for under-slab insulation, but XPS is more vapor retardent, and has a ~25% higher R value for any given thickness. EPS is usually cheaper per unit-R.BTW: XPS is never white beads, EPS is. Both are good for under-slab insulation, but XPS is more vapor retardent, and has a ~25% higher R value for any given thickness. EPS is usually cheaper per unit-R. Yup. Thanks. I always get my "ex's" confused.

check out thecompleteinspection.com on the trendy new internet.