I would like to build a 6 x 8 ft playhouse with a deck covering the top. Is there a kind of roofing material that can (1) withstand a floating deck, (2) is DIY friendly (no blowtorches, hot asphalt, or custom pouring), (3) is reasonably cheap, and (4) will keep the water out even with a completely flat roof, or with a very minimal slope?
Modified bitumen is said to be great for building deck on top of. The GAP SBS Liberty system is DIY-friendly, but the instructions call for a slope of at least 1/2" per ft. If using only the cap sheet, it's about $1/ft².
Building a deck on top of the roof is much easier if the roof is completely flat. Is that asking for trouble, or will it be OK for my application?
Are there other roofing materials I should consider?
Best Answer
EPDM rubber roofing might work for you. It can be installed without any heat or fancy tools; I'm planning to use it for my flat-roofed concreted detached garage. It should withstand ponding water, and because your project is small and your playhouse probably doesn't have plumbing, you should be able to avoid seams, complex flashing, and pipe penetrations. You can install the rubber using an adhesive directly over clean plywood.
It can accommodate a floating deck. I have the book Roofing, Flashing & Waterproofing (For Pros By Pros), which includes a nicely illustrated article on installing EPDM with a floating deck. The method they recommend is to use a non-adhered strip of EPDM underneath the decking sleepers, so that any motion in the decking doesn't stress the roof membrane much. You'll still want some slope in the roof for better drainage, but you can compensate for that in the sleepers, allowing you to have a level walking deck.