Torch-down bitumen

For low-slope roofs such as this, regular shingles are not allowed by code. Here I'm using torch-down modified bitumen. The black underside gets heated with a flame, then melts slightly and adheres to practically anything. There's a base sheet of roofing felt made specially for the application. It's in turn nailed to the plywood with basesheet fasteners -- short, ring-shank nails with large built-in plastic washers.

At where the existing valley comes down toward the skylight curb, it's especially tricky. The roofing contractor added extra layers of bitumen with the last one tucked underneath the existing flashing.

Needless to say, this seam is critically important. Rainwater that channels down the valley flashing should not sit in any kind of puddle, which is easy with a low pitch roof deck and nearby skylight curb. Then the top layer of metal tiles must be nailed to something and drip over everything. Hopefully that last step comes together okay.