CaleyAnn wrote:John, Are you saying I could spray foam over the entire area, then trim it back flat. Then just glue something over it. Hmmm..... still have that can of spray foam which probably has enough to do the job. Guess I will have to find a way to contain the foam until it dries. Also need to lay down a lot of painter drop cloths. Maybe after it is dry I coild just use fiberglass and epoxy, then paint it with a wood looking paint.
Sorry, I've lost the context.
But no, sawing the sprayed foam where it's protruded past the surrounding framing is a pain for large areas, but can be manageable for just some "peaks".
Trying to do that in order to get a flat surface to mount a flexible lining directly to the foam would be a major PITA!
I meant rigid foam board as the next-to-innermost layer.
Using that last as the inner wall of a "mold" box, which is then filled with spray or poured foam could work, but the expansion force can be **very** strong, and you want the excess to ba able to freely escape.
Better to fill the space with rigid boards as much as possible, it's cheaper and better R-value anyway.
Then the spray is just for small gaps and voids, ensuring a complete envelope.
Having a nice flat secure surface then makes 'skinning' with your interior liner relatively easy.
But having structural furring strips to mount a more solid sheet to with screws is better, especially if access is needed for later maintenance.
It also lets you put in a proper vapor barrier of plastic sheeting.