foam insulation cavity fill question?

Old 12-22-08, 03:42 PM
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foam insulation cavity fill question?


I live in the Philadelphia area and had a guy quote me to inject "Tripolymer" foamed-in-place insulation into the space between my brick veneer outer wall and the inner wall of my house. The space is about 1.5 inches wide and he says it will help seal the building envelope as well as give me an R-5 to R-8 insulation blanket on the walls of my house. The foam is relatively new I think, it's not the expanding polyurethane type, but rather a water-based, pre-expanded type, I think similar to Retrofoam, which I've also found online. My concern is whether it could be harmful to fill in that space between the brick and the inside wall in terms of moisture build-up and so forth. Thoughts?
Old 12-26-08, 06:33 PM
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It's all about where the vapor barrier is. Building Science Corporation has some good reading. Specifics on vapor barriers is at Proposed Vapor Barrier Code Changes —

If it can be done without creating moisture problems, go for it.

Tripolymer is a brand name: C.P. Chemical Company, Inc.-- Manufacturers of Tripolymer Foam Products for Insulation and Tank Abandonment

Can't seem to find whether it will absorb water, or is open- or closed-cell.
Old 12-28-08, 07:21 AM
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Question for you: is there actually no insulation at all in those walls now?

Old 01-06-13, 02:52 PM
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All non-expanding foam insulations contain water in the product mixture. Thus when curing, the insulation will shrink. Tripolymer HUD specs say it shrinks from 0.5%-1.5%. That means, in the width of a a standard stud space (14.5" width), it will shrink, during cure, leaving roughly 1/32 - 1/8" gap between the studs and insulation. A clear path for moisture vapor to move.

The perm (permeability of moisture vapor transmission) rating of tripolymer insulation is 15.9 - 16.9 per their data sheet. 15 lb. asphalt impregnated building felt is around 5.6. Extruded insulation, like the Dow Blueboard is less than 1/2 of 1%, as a comparison. So moisture vapor will flow thru the tripolymer, but at a much lower rate than an open cavity or fiberglass batt filled cavity.

Also, that "gap" between the facebrick and stud wall is a drainage plane for any water infiltration from the exterior. That "gap" also makes it difficult for any water getting past the facebrick and wicking into the wood products of the stud system, either by a failure of the watertightness of the masonry system or by wicking thru the masonry material. Talk to anybody associated with the Ntaional Concrete Masonry Association and they will tell you to NEVER fill that gap with insulation.

Last edited by ken-r-mer; 01-06-13 at 03:15 PM.
Old 01-06-13, 03:10 PM
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carl -

I know this is an old post, but the basic principles of proper construction do not change.

From your description you have a classic cavity wall that is not intended to have insulation in the 1-1/2" to 2" cavity between the interior structure that provides a barrier from wind driven rains, a gap that provides ventilation and pressure equalization.

Insulation should be between the wood framing studs and not clog up the cavity for maximum efficiency or a layer of XPS foam board that still allows air circulation.


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