Do it Yourself: Re: [DIY] Closed Cell foam insulation

23 January 2013

Re: [DIY] Closed Cell foam insulation

If your walls are open sprayed closed cell foam is the best way to go, but it is not cheap by a long shot. You may also want to be in a position to leave the walls open and give the new foam time to gas off before sealing with either sheetrock or siding. Keep in mind that once you close those walls in you will not be able to fish wires or anything else through them.

Dale in the Flatlands.

Strat wrote:

Recently I read a debate in fine home building mag on benefits of retrofitting an old homes exterior with 2-inch closed cell "rigid sheets", y'all can look it up if you're interested in reading it. But the long and short of it is:
My old home which probably has no kind of insulation in the walls and that makes the house hard to heat during winter.
Having researched options, I see basically 4 possible approach to insulating the walls:
1-spray closed cell foam between the studs and button up with new siding.
2-spray open cell foam, which costs less but doesn't have vapor barrier properties of closed cell.
3-fill the cavities with damp cellulose
4-cover over the studs with 2" sheets of rigid foam sheathing, tape the seams, cover with a wrap, then apply the siding.

Its this last approach that's got me fired up.
I don't understand why you would build up the exterior thickness over the studs by 2 and 5/8, that's crazy.
Not only does this pose new problems for re-flashing all the doors & windows, but also I wonder how the heck is the exterior siding going to attach to the studs with 2 and 5/8 space between them!?
It seems 4 inch galvanized screws would be the only option, heck you can't secure the siding to foam!!

My preference is to shoot closed cell foam in the wall cavity every 16 inch. This ensures all the walls, electrical outlets, sills and ceiling transitions are sealed tight with a vapor/moisture barrier which offers better R value per inch than the other options.
You can then wrap that with Tyvek and nail in James Hardi boards with a nail gun, bang bang bang, you're done.

No need to spend a lot of extra money on foam fastners, and 4 inch galvanized screws for securing siding to the studs. Best of all, I preserve the original thickness over the studs and minimize the need for custom flashing around windows.

There is yet another evil which is sizemic movement here in California the ground moves! These foam sheets are not speced to be sheer walls and I would not bet that in a year or two the tape that seals all those seams is going to hold "air-tight", in fact I bet it won't.

In closing I'm no expert, just a home owner, but I honestly don't see the logic in wrapping the house with rigid foam sheets.