Spray foam insulation attic
user-7857441
| Posted in Energy, Heating & Insulation on
I will be building a home in the northern (cold) climate and will be using spray foam insulation. I am playing with the idea of sheathing the entire attic with 1/2″ OSB and then spraying the insulation from the underside before the drywall is installed. Has this process been done before and are there any pitfalls with this method
Replies
Do you mean the bottom of the attic space? Or the roof decking?
The bottom of the attic space.
Yes, there are pitfalls.
You can't have a composite roof over that. You need steel or similar.
In order to reach an r45 you will need 7 inches of closed-cell foam. If your rafters are not deep enough you can strap it out and place spacers as needed.
If you fill a 2x8 rafter space with foam you will have no room for any changes to wiring.
I’m thinking they are talking about foam between the living area ceiling and the attic floor.
That is correct. Ceiling drywall, joists with spray on foam and OSB nailed to the top of the joists. Basically, an attic floor that is installed as part of the framing effort. Which would require all the trades to finish work, then spray insulation from the living area, then ceiling drywall
So you can use the attic for cold storage, I guess. Just build it taller is what I'd say and fill. Calculate the thermal bridging of the joists.