Spray Foam Insulation

[Retired Guy]

We are considering re-insulating our 1970's house attic. We currently have 6" of fiberglass on the attic floor. Spray foam installers have suggested removing the current fiberglass and either spraying the underside of the roof deck, or spraying the sheetrock on the attic side of the second floor ceiling. Any pluses or minuses for either plan?

 

[gzecc]

Didn't know there were such old houses in the US . I personally don't like spray foam, because of the problems caused by doing future work. Everything gets hidden with in the foam. Forget about snaking wires.

 

[yooperdave]

A couple of members have had their houses spray-foamed and seem to really enjoy it. They haven't said much about it since the project was completed. One word of caution, I heard that some products "shrink" over time. I wish our house could be spray-foamed, but due to the construction, it can't be...not enough room for the hose and head apparatus I was told by the rep.

 

[woodgeek]

Did you get a quote for spray foaming the roofdeck yet? If not, let us know afterwards. Compare the quote price with blown cellulose over the floor at $1.50/sq ft to R-50. Personally, I think roofdeck foaming has a poor ROI, and you want a good experienced company....if they screw it up or get a bad batch (i.e. doesn't cure properly, stinks, etc) it is very hard to remove/redo.

That said, I am currently going to have a spray foam outfit airseal the top plates along my soffits for ~$400. I can't reach them myself with a caulking gun.

The wall cavity stuff is a little different than the polyurethane they do in attics.

 

[semipro]

WRT the original question; one way creates more climate controlled space (your attic), one does not.
Also, there are likely air leaks between your interior and the attic. Sealing with foam between the attic floor joists will provide both thermal insulation and air sealing.
You can get the same effect by removing the fiberglass, sealing everything up, then blowing insulation back in. I prefer cellulose as suggested by woodgeek. Only limitation here is how much R value you can get given the height of your attic floor joists. If its not enough, you can attach 2x4s to make them taller allowing more insulation to be blown in. The 2x4s are only needed if you want to be able to walk around or add flooring to your attic. Otherwise just overfill the bays with blown insulation.

 

[woodgeek]

I am **finally** upgrading my attic insulation, after getting the air sealing done and having a $$ incentive from the state (essentially 10 yr 0% financing).

I am doing blown cellulose over the crappy/ancient FG batts and blown that are there now. I don't have an unfinished basement, so the attic storage is pretty key. I decked maybe 150 sq ft (with new R-20 FG insulation underneath), the contractor will build a 'dam' around this, and blow the other 90% of the area to R-50+, for ~$2k. I estimate simple payback at ~10 yrs.

I just don't see the advantage of foaming the roofdeck, unless the roof is high enough to enable use as new living space/playroom/etc.

 

[Highbeam]

Mass foaming of just about anything is not a good idea. Not until prices come down. Especially in an attic, foam is a poor economic choice. It is so cheap and easy to build R-value in an open attic.