What’s goin’ on! Rigid foam insulation / WRB shrinks?
I did not join GBA until after the issues of “shrinking foam” were discussed. I used it for a WRB/exterior insulation combo without having understood that there might be an issue. I used Tuck (sheathing tape), Weathermate flexible flashing and Windlock cap head screws to install it. Topped up with Vytec (division of CertainTeed) split shake style siding.
Earlier this week I read the FourSevenFive.com’s recent series of “Foam Fails” articles. This is undoubtedly very controversial and has serious legal liabilities associated with it.
http://foursevenfive.com/foam-fails-reason-5-excessive-shrinkage/
What I would like to know is, what is real issue with my insulation and WRB “system”: performance impacts on the house, air leakage, lost of R value, condensation, increased heating and cooling costs.
If the rigid foam shrinking in cold weather, expanding in warm, or is the shrinkage permanent like the photos and bloggers discuss.
What is really going on? Can I trust Pactiv, Dow and Corning products? I was not forewarned nor advised when I purchased the products that these risks exist.
Would I have used this system and productgs if I had known? I would have at least used a seperate WRB (like I did on my roof deck). I would have at least caulked and used adhesives for the seams and joints like I did with all my sheathing and framing.
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Replies
Flitch,
In case you haven't seen it yet, here is GBA's article on the topic: Using Rigid Foam As a Water-Resistive Barrier.
Flitch,
If your foam shrunk, it's permanent. There's no need to get worked up over an article informing professionals unless you know for sure that your foam shrunk.
I did read your piece, Martin. So there are no data or studies on what foam is really doing? Isn't Joe L's experience the truth on the matter?
Flitch,
We have anecdotes, not data. The advice I gave in my article still stands: if you are worried about this issue based on the anecdotes, use a conventional WRB like plastic housewrap. Another advantage of conventional housewrap: it's much easier to integrate with flashings than rigid foam.
There is one other point worth bringing up: even if tape fails, and even if foam shrinks, the presence of a ventilated rainscreen goes a long way toward protecting your house. A wall assembly with a ventilated rainscreen is very forgiving. Even if some liquid water gets past the siding, and even if your tape is curling, and even if cracks open up between the foam, a ventilated rainscreen encourages rapid drying.
That said, I still think that housewrap is a better WRB than any type of rigid foam.