Open cell or Cellulose inside Closed Cell barrier
Hi Everyone,
Looking for a couple opinion answers on a project I am doing. We are going to do 2 inches of closed cell foam inside a new construction home to vapor / air seal it as best as possible, The next step is where im a little stuck.
The home is built usiing double 2X4 walls, so the rest of the insulation will either be open cell or cellulose to fill those bays. Ive been reading alot of horror stories about foam off gassing forever and causing problems. Would there be a downside to going cellulose inside the closed cell? I figure its a much more inert material and wont cause any chemical based problems, but may be more likely to mold. The building is a gambrel colonial with a walk out basement, so the basement walls will be insulated as well, ive already got R20 xps panels and solar radiant under the slab in the basement.
Any opinions? I will be insulating in a couple weeks, just finishing up plumbing and electrical now.
Thanks so much in advance
Denis
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Denis,
You didn't mention your climate zone. It's always helpful to know where the building is located.
Two inches of closed-cell foam will provide you with about R-12 or R-13. If you fill the remainder of the 3.5 inch cavity with cellulose, you'll get a total R-value of about R-18. That's not a lot.
To answer your question, there is no reason to think that the cellulose in such a wall will grow mold.
If you are worried about potential off-gassing from spray foam, perhaps you shouldn't use it.
Well Im really just trying to limit the risk of doing so much spray foam. My wall thickness will be 1 foot inside to inside. i should be closer to r45 or 50 when Im done. The spray foam closed cell is to.help me seal it up a bit both the 6 dormers.
The home is in Connecticut so that's zone 6a.
Denis,
Sorry -- my mistake. I misread your original post, and I missed the part about double 2x4 walls.
It sounds like you wall will perform just fine.
Denis: If you are primarily using the spray foam for an air barrier/vapor barrier, and are concerned about it, why not skip it and air seal w/ a different method? Are you sure you need a vapor barrier as opposed to retarder?
Spraying foam in the winter is the worst time to do such. Go to two or three of your contractors jobs and make sure you are happy with the work and the smell. Close cell must never be sprayed too thick. Never.
Insulation and air barriers should be planned out prior to digging the foundation hole and should be on the plans that were submitted for your building permit.