Redoing a low slope roof, 1-12. Installing 5″ of rigid foam (GPS) on the deck, wondering what the value of taping the seams would be. There will be two layers of foam, 2″ and 3″, laid  with seams opposite each other. It’s an 1800 sq ft roof, so the taping isn’t a small job, on two layers.

The whole assembly is below, what would I gain for the extra cost/time of taping?

Flex Membrane, 3″ gps, 2″ gps, deck, 8″ open cell foam, vapor barrier, drywall.

Thanks!