Hi Simon, with the overlapping nature of the felt roof shingles and the angle of the roof. The rain water will simply run down the surface of the shingles and into the gutter. On a flat roof where they do not have natural drainage, a drain will be installed to act as an outlet for excess water, to prevent it from pooling on the surface of the roof.
So you've basically felted the roof and then put shingles over the top? I'm looking at doing this on a gazebo, confused to as why you've used double coverage. Why not just membrane then felt it with shingles?
