I had been a DIYer for 35 before retiring and then starting a home improvement business. I've pretty much "reitired" for that also now but am helping a friend replace a deck that had been constructed over a torch down roof. The contractor glued the sleepers to the torch down roof and then screwed the decking to the sleepers. We have stripped off all the old work managing to remove it all and finding only two small holes through the torch down because the glue just wouldn't let go! Almost all of it, however, was not adhering at all. I used roofing tar and a tar-impregnated mesh material to patch over the holes. They want to use Ipe so I have read everything that I can find online plus visited East Teak Fine Hardwoods in Donalds, SC for a discussion with George Guy. He was very helpful with issues relative to water runoff and ventilation. I plan to install 5/4 x 4 Ipe with a 5/32 inch gap over sleepers on 16 inch centers using two 2-1/4 inch stainless steel screws at each intersection. I plan to glue 1/2 inch concrete expansion joint material beneath all sleepers to protect the torch down roofing. They would like for me to "recoat" the torch down material before installing the new deck! I have explained that torch down is not just a coating but rather is a roof covering (in 25 words, or less!) and I don't really think it needs a "recoating". Their "water damage below problem" wasn't caused by the roof leaking but rather by incomplete sealing beneath some pillars so that water could get under them and make its way to the porch roof below by way of the holes drilled for electrical wiring inside the pillars (there is an electric lantern on top of each pillar). My question, then, is: "What can be applied above the torch down to seal it (and put the homeowners mind at ease) if that becomes necessary?"