Commercial spray foam is a roof-deck job. It puts the attic inside the building. A vented attic over a ceiling is still a blown-in job.
- Open-cell
- About R-3.6 per inch
- Closed-cell
- About R-6.5 per inch
- Occupied rooms
- Thermal barrier, usually gypsum
- Two inches
- An air seal, not the finished R
When commercial spray foam is the job
Spray foam goes on the roof deck when that space should be inside the building. It is the right call for a hot roof over an office, a bonus space, or a warehouse that should not stay a vented attic. It is the wrong call for a vented attic whose ceiling is already the boundary. That attic gets blown-in.
Open-cell is about R-3.6 per inch and vapor-open. Closed-cell is about R-6.5 per inch, and at roughly 1.5 to 2 inches it is also a vapor retarder, depending on the product. Two inches of closed-cell is about R-13. That is an air-seal coat. It is not the R-38 attic number, and it is not the above-deck roof number.
Fire barrier
Foam left exposed to an occupied room needs a thermal barrier, usually gypsum, unless the exact product is approved without one. Foam in an attic or a crawl space that is not occupied can use an ignition barrier, or a system listed for that exposure. Bare foam because the schedule ran out is not a finished commercial job.
Foam smells while it cures. The building has to be empty of people who cannot leave the smell. We say so before the day is booked. A store that stays open is not a foam day.
One boundary
Do not foam the deck and leave the attic vented. Pick the deck or the ceiling. A mixed assembly wets the deck. A roof leak is fixed before foam goes on it. Foam is not a roof repair.