looking at insulating my ceiling on a 2400sqft full ICF house with full ICF basement.  The roof is a 7/12 pitch with lots of gables and jut outs.  I was thinking of maybe spraying a coating 1-2" thick on the top of my drywall then placing blown in to get to an r60is.  I should mention that I am located in Saskatchewan, Canada.  What i am wondering is if there are any drawbacks to this method.

I would place all electrical items such as lights, and air to air exchangers for bathrooms etc in prior to drywall then spraying the foam.  Just wondering what kinds of problems people can see down the road.

For example I would expect that if I needed to remove ceiling drywall for some reason this would be very difficult with the spray foam, not sure what other potential issues I may have??

Any thoughts.

Thanks

It's not that tough to cut holes in 1/2" gypsum plus 1-2" of closed cell foam, and re-foaming to seal any patched in sections is easily done with a FrothPak kit from a box-store. The fact that it glues the gypsum facer to the joists or truss-chords would mean a bit more clean-up with chisels or reciprocating saws prior to patching in a section, but I wouldn't sweat that too much.

I'm doing an "attic seal" on my ceiling prior to blowing insulation. Basically after the drywall is installed and the first coat of mud, they will foam all wall to ceiling connections from above to seal them up, as well as foam all electrical boxes from above, fixtures, etc. Things such as bath fans will get wrapped in batt and then foamed up and over the batt to seal it but still allow some flexibility within the batt. I have in ceiling speakers as well, and I built 10"x10"x5" plywood boxes and attached them to the joists. This will allow the boxes to be foamed and sealed, leaving a nice clean air tight space below when I cut the gyp and install the speaker. Attic baffles are also foamed in place to the roof and to the top plate of the ICF wall. This will seal this location as well from wind washing the blown insulation. Its very similar to your approach, however a cost savings due to not spraying the entire ceiling plane, rather just the joists where most leaks are. R60 will then be blown ontop.

Posted By lzerarc on 18 Feb 2013 11:03 PM
I have in ceiling speakers as well, and I built 10"x10"x5" plywood boxes and attached them to the joists. This will allow the boxes to be foamed and sealed, leaving a nice clean air tight space below when I cut the gyp and install the speaker.

Not an insulation issue but watch out on the speaker boxes. Depending on what kind of speaker system you plan to put there you may need to provide an air tube back around to the room space or up into the attic. An air tight box will distort the speaker performance because the cone will compress and expand the air behind it as it moves back and forth. That can radically impact the sound quality.

I have wondered about that as well. I am using Polk speakers, 6" round, RC60i. The thought was I could add a 1" ceiling port hole if needed beside the grill if needed. Think that would work?

Normally the vent and enclosure for a speaker are carefully tuned to increase the bass performance. If not, oversize both to avoid a mid-bass resonance.

Posted By lzerarc on 19 Feb 2013 09:17 AM
I have wondered about that as well. I am using Polk speakers, 6" round, RC60i. The thought was I could add a 1" ceiling port hole if needed beside the grill if needed. Think that would work?

Top notch speaker design is a complicated mixture of art and science. If sound fidelity is a distant second to the convenience and presence of the sound then you'll be OK. You may have to experiment some. If fidelity is a priority then you need to figure out how to use quality fully assembled speakers.

The only place I've ever really used self assembled speaker systems is in a shower!

How did you spray foam job go?  I am looking at a couple of inches and then fiberglass.

How did the attic seal turn out and in particular how did  the sealed in speaker enclosures work.  Did you insulate or provide sound stuffing inside the speaker enclosures?l