Spray foam in walls
Katrin Klingenberg of PHIUS gave a talk called “Balancing the Investment: Enclosures, Mechanicals, and Renewables” which is available on demand from the Energy Center of Wisconsin.(1) At 25:00, she makes this comment on many houses with spray foam wall insulation applying for Passive House certification: “We have seen applications that are horrendous. The walls are going to be full of water in two years.”
She’s probably exaggerating about the time scale but I’m still trying to figure out the cause of what she is talking about. Is it condensation in the walls caused by not completely filling the wall cavity? If so, is the only solution to overfill the cavity and trim the excess with a foam saw? In most examples that I’ve seen, the wall cavities don’t get completely filled. Here’s one example on youtube. (2). The narrator says that he tries to get within 1/2″ of filling the cavity. Is that a problem?
1. http://ecw.mediasite.com/mediasite/Catalog/catalogs/betterbuildings.aspx — on page 3
2. https://youtu.be/bEwKpY1wsb8
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Replies
David,
The only person who can answer your question is Katrin Klingenberg.
By the way, I went to minute 25 on the presentation, and I didn't find the quote you referenced.
My guess is that Katrin worries about voids that are large enough to allow exfiltration and condensation. But that's just a guess.
I do know that Katrin is an advocate of cellulose insulation and blown-in fiberglass, and that she discourages builders from using spray foam insulation.
Ok. Thanks, Martin. Maybe I didn't get the timing or wording exact, but I think 25:00 is very close. The excerpt I was referring to may be like 15 seconds before or after. I think it was during the discussion of her slide number 17. I got to run to work so I don't have time to look it up right now.
Anyway....is the best/correct way to install spray foam in an exposed wall cavity to overfill it slightly and cut off the excess? I see a lot of foam contractors not doing that. They just get as close as they can without having to go the extra step of cutting the excess. Energy star stresses that, with whatever insulation is used, it is critical that all sides of the cavity be completely filled.
She does go on to briefly discuss cellulose and fiberglass. Loosely quoted, "We would love to use more cellulose but it doesn't have the R value of high density fiberglass." I hope I'm not misquoting. I'll check it out when I get off work tonight to make sure.
David,
OK - I realize my error. There were two Katrin Klingenberg presentations on that page, and I clicked the wrong one.
I think that she was talking about houses with thin rigid foam on the exterior side of the wall sheathing. If the rigid foam is too thin, it won't keep the wall sheathing above the dew point during the winter. This is a point I have emphasized many times: thick foam is safer than thin foam.
For more information on this issue, see Calculating the Minimum Thickness of Rigid Foam Sheathing.