Who knows Icynene well?

[V-10 Killer]

Every application I've seen so far shows it sprayed on the inside of the roof deck for an unvented attic senario. Or into wall cavities, then drywall installed over it.
But some installer websites state that they can fill wall cavities of older uninsulated houses with it too.
Would there be a problem if it were applied directly to the top of the drywall and trusses? It looks like it stops expanding in 10 seconds or so. I don't think it would push the drywall away from the truss like Great Stuff® expanding foam has been known to do in between studs and doors/windows. After it dries in 10 minutes or so, it would essentially glue the drywall to the truss, helping (a little) to support the drywall as opposed to making it sag.

I would like to do this in my vented attic, but haven't seen any pics or stories of it done yet.

What does everyone think?

 

[PAToyota]

If I'm reading your question correctly, you're asking if you can go up in the attic and spray it down onto the exposed drywall and trusses? If so - most definitely!

 

[Franz©]

There are thousands of preassembled panels being made every week and shipped to hurricane country employing foam to adhere the drywall to the rafters and no pther fasteners used.

 

[V-10 Killer]

Thanks a bunch.
I kinda knew the right answer, but in 2 hours of internet searching different word combos, I couldn't get a difinitive answer.

I imagine this is the same stuff they inject into garage doors and water heater jackets and it doesn't do them any swelling damage.

 

[Franz©]

2 component foams injected into cavitys do not swell if there is sufficient releif space for the expansion.

Too much foam or too little releif causes swelling.

 

[PAToyota]

If I understand you correctly, you are not spraying into an enclosed space? Just on top of the drywall and trusses? If that is the case, once it is dry it will not create any downward "force" on the drywall to make it sag - it will pretty much be self supporting and tie to the trusses.

If you are talking about injecting it into a closed wall space - between studs with the drywall already on the inside - then it can be done as long as the installer does not fill up the stud bay too much as Franz states.