I've used it on some projects and didn't notice any significant off-gassing. We didn't do any testing to come to that conclusion, but it didn't smell like chemicals or anything. These were on spec homes, so I didn't live in them and I can't speak to any other adverse effects. I am preparing to finish out a living space on my own property and have been looking into this for my own purposes and have discovered that vented or unvented roof assemblies, insulation, vapor barrier choices is pretty complicated (I'm an engineer and I don't totally "get it" myself). I'm leaning towards not using spray insulation and just having a less efficient structure might be the way to go from a building longevity standpoint.
Here's an interesting article from the Building Science Corporation that is probabbly the leading authority on this stuff:
https://buildingscience.com/documen...bsi-016-ping-pong-water-and-chemical-engineer
Makes a big difference in what climate zone you're in as well, so take that into consideration. I'm in climate zone 7 and condensation developing on the underside of the roof decking is almost a given.
https://www.energy.gov/eere/buildings/building-america-climate-specific-guidance
View attachment 1004076
I'm not sure what your budget is, but I would think spray foam to correct R-value on underside of roof deck and a climate controlled or semi-controlled attic space would offer the best condensation control. Some of it is going to depend on the dew point. At zone 7 temps it will likely require a boatload of insulation or an uncomfortably dry house to meet your goals of condensation control.
You also want to make sure the substrate is the correct temp and clean and dry to get good spray foam adhesion. If not, you get air gaps between the foam and substrate and water will condense in there and rot the substrate. Also, make sure you get enough insulation coverage on the rafters/top chords of the trusses, as those will be the transfer areas for radiant heat loss/gain.
There are formulas to find the point in the wall assembly where condensation will occur at various temps/dew points/R-values. I don't have anything saved on my phone, but they are out there.
The only other great options are venting. In zone 7 you are going to need an exceptionally sealed building envelope especially at the ceiling/attic. Wire penetrations, duct work, and plumbing vent pipes, and lighting will all leak heat/humidity from your house and cause potential issues.
I work in zone 5a and normally we don't see a lot of issues with this. Most issues are catastrophic, as they are a result of very elaborate houses build with normal shitty building envelopes and zero thought given to controlling this. Then they pump humidity into the house all winter to keep the woodworking from shrinking. When we get weather that is colder than climate zone averages, those types of houses have massive damage from frost forming on the roof deck and then melting. It rains inside. It is not a well known issue because it so rarely gets that cold here. All of my clients that have had this problem have called with a roof leak no one can find and it turns out to be this.
As far as off gassing, everything that is solvent based off gasses. The question is for how long and to what effect. I honestly don't have a great answer to the question with spray foam, but I would bet there is published research out there to shed some light on it.
