Quote Originally Posted by garymunson View Post
I'd still be concerned about roof leaks. A plumbing leak is an entirely different animal....constant flow of water that will eventually show up somewhere. A leaky roof will provide a sporadic injection of water into the decking and trusses. As far a someone never having a roof leak...interesting how there seem to be a fair amount of people employed re-roofing structures. Of course if you move from new house to new house on a regular basis you may never experience one but here in Florida I have seen many roofs that looked fine leak badly. I'd feel better if the foam could somehow be applied above the actual roof structure as on commercial buildings with flat foam roof. In those cases, failure of the roof membrane is obvious.
That is a pretty good way of doing it.
5/8" decking applied to top of rafters.
self healing roofing membrane applied to that.
4" to 6" of polyiso foam insulation - 4x8 sheets - about $.50 a board foot.
1/2" decking on top of foam with long screws and washers going through 1/2" decking and foam into 5/8" decking
Whatever roof you prefer on top of that.
The top layer of 1/2" decking can be replaced as needed when the roofing is replaced.