Attaching rigid foam below ceiling rafters
I’m building an insulated shed, with a ventilated flat shed roof. I’m planning to hang rigid foam below the 2×6 rafters in order to avoid the hassle to cutting them to fit in between. But how many inches of foam can I install so that I can still fasten plywood beneath, screwing directly through the foam? I’m hoping for 3” of foam, but that would require very long screws.
When installing the foam, should I use flat washers? Thanks all,
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