Sealing Exterior Foam-Board
I tried this earlier in the wrong category so I thought I’d try again here…
I’m building some walls per the Building Sciences Corp recommendations for very cold climates. Some of their drawings show the exterior foam board sealed to the top and bottom plates, and others don’t. Also, they show sealing the drywall to the plates (presumably as a vapor barrier), but mention plastic as a vapor barrier elsewhere.
Does anyone know the correct way to do them? I’m tending toward using plastic on the inside and sealing the foam board with latex caulk to the top and bottom plates, and in the joints (tongue and groove). I certainly don’t want to trap moisture in the walls, however. BTW: I’m planning to use wet blown cellulose as insulation and am using 2×6’s for studs/plates.
I will appreciate any help that I can get. Thanks!
Replies
Rich,
If you super seal the plastic vb on the inside I would have difficulty with sealing the board on the outside.
Gabe
ya, seems if you would do that you would want to vent the walls somehow.
"seems if you would do that you would want to vent the walls somehow."
I find Building Science to be very difficult to follow on venting issues; be careful in reading those pages. Very good site and information, but not for skimming!
Are you going by BS web site or do you have the book.
The book has many variations in assemblies in it and list some of the pros and cons.
If I remember correctly the book on cold climates specifically does not recommend that comindation foam, wet blow cels, and plastic. The reason is that it is often closed up before the cels can completely dry out.
Edited 5/31/2002 12:16:22 PM ET by Bill Hartmann
Bill,
I was going strictly by the web site. I wasn't aware that they had a book covering their techniques. I'll go back and see how to get my hands on it.
I agree with Bill - it's hard to reconcile the different information that they show.
I really want to avoid venting the walls. It seems kind of self defeating to work real hard to stop mosture movement and then have to resort to complicated ways to vent them. Sort of like building a really tight house just to install an air exchanger :)
Thanks to all for your thoughts - I guess this thing really does work!
Rich