I have a small woodshop (950 sq. ft.) in the loft of a barn that I am planning on insulating with spray foam. I’m going to use the fire rated stuff, and will probably leave the rafters exposed and just use the foam (3 or 4 inches) and “flash and bat” the walls (1 inch of foam to seal followed by fiberglass bats). I could save some money by using the flash and bat method on the underside of the roof also but am unsure if that would cause a problem since there won’t be any ventilation. (????)
I’ve been looking at the do-it-yourself kits, not so much because I begrudge hiring someone to come in and do it, but because I can’t imagine moving stuff away from all the walls at once so a contractor would have access to the whole job at once. There’s a lot of stuff in the shop and I figure doing it myself I can do one wall, move things back into place, then move on to the next wall another day. The sources I’ve found look like the material will cost me about $1 per board foot (ouch!)
I’ve never done this before so I’m hoping that someone who has experience and has used this stuff can comment on whether this seems like a feasible/reasonable way to go about it?
thanks, Mark
Replies
We have a bonus room that's paneled w/ 2 big walls against the attic. It's ridiculously leaky, air-wise, and I'd pulled off all the old FG in preparation to try to fix that and reinsulate. Rather than try to detail each board w/ caulk, then batt, then put up rigid foam board over the framing, I opted to spray the whole thing w/ 2-lb polyurethane.
I looked at the kits and got a quote from a contractor a friend had used w/ good results. Having someone else do it cost only about $150 more than buying the kits. For that, it was worth it to minimize my hassle. And it's fairly close to what I've read generally about DIYing insulation vs. paying an installer- no matter which kind, the installer's getting a good enough deal that the installed cost isn't much more than you'd pay for the material.
The other thing to think about a little is that trying to spray on an inch isn't going to be very precise at all. You'll end up with lots of bumps that'll compress the FG you put up over it and make it less effective. Picky but true.
I don't know if the lighter-weight foam (0.5 lb) would be cheaper. But I have such a backlog of DIY work to do that getting this one task out of the way was worth a couple hundred. YMMV.
Have you considered or priced using rigid foam insulation as the first layer with a expanding foam to fill in the gaps? You could leave 1/4" around the edges and then go back with the expanding and have the same effect. I am considering doing a large hip roof this way for some of the same reasons you have mentioned.