I am trying to find least expensive method to install support for spray-on closed cell foam insulation between ceiling joists in attic where there is no support beneath the rafters (only a drop ceiling). This is a large fire station that currently has fiberglass bat insulation between the rafters. Any ideas are welcome. Thanks, Bob
lay sheet plastic over ceiling and then spray the foam over the plastic. Make sure the foam goes over the ceiling joist as well as in between. Whe the foam becomes rigid, it will support itself with the portion that has dried over the ceiling joist.
The plastic might tear or sag when the weight of the foam is applied. You could staple thin sheets of underlayment or OSB to the bottom of the joists then spray the foam from the top. Basically, you are trying to keep the place warm that has no ceiling and any heat goes up and around the drop ceiling, thru the insulation and out of the building. That's how I understand your problem. Maybe you should just remove the suspended ceiling, nail up drywall and use the existing fiberglas between the joists with another fiber glass layer perpendicular to the joists on top of the old stuff. Or blown in insulation. You better test the foam for flamability. Some of that stuff can burn and emit toxic fumes that will kill a whale. The other disadvantage of foam is that moisture will not penetrate it, so you might have condensation on the ceiling. Drywall will allow moisture to pass thru and sheathing and Tyvex are also designed to breath. You don't want to trap moisture inside any place you live. That would create a whole bunch of problems. Black mold being one of them.
remove ceiling put plastic on rafters spray foam it will adhere to the rafters
