We recently completed this insulated flat roof repair in Miami Lakes. The existing flat roof over the Florida Room was leaking close to where the valley of a concrete tile roof spilled on to it. The flat was a modified bitumen BUR over 11/2” of insulation.
We removed two rows of tile at the tie-in and about 5’ up the valley, then opened the modified to reveal some very wet Poly-Iso insulation of which we tore out a 4’X4’ area along with about 10 ‘ of tapered edge at the transition. The amount of water we found was somewhat surprising since the leak was described as small. We soon found out why; there was an old smooth 3-ply fiberglass roof underneath. I was never so happy to see a roof-over in my life! As a result, aside from minimizing the roof leak inside, there was NO rotten wood what-so-ever.
We put down a piece of composite board, new tapered edge, 1 ply of Gafglas#75 and ran 3 1/2” screws and plates though it. Next was a layer of Ruberoid Torch Smooth and then Ruberoid Torch Granule. We doubled-up to get flush with the old roof and avoid ponding at the bottom of the valley. Ran the rubber up the valley, nailed down the valley metal and stripped it; then put the tile roof back together with some foam and mortar and we were done, right? Wrong! We installed a 1-way vent as there had to be some trapped moisture.
Also, the tile roof and flat roof were both almost 20 years-old, so while the tile roof could last at least another 10 years, the flat roof’s days were numbered without some serious maintenance. There was some moderate ponding so we applied 2 coats of Somay 814 Rubber solvent-based roof coating and re-enforced the seams with 3” fabric. Done!