Metal roof question – GreenBuildingAdvisor

Kevin,

If you install your metal roofing directly onto the WRB, the amount of moisture that accumulates on the backside of the panels is negligible.

Here’s how I flash roof penetrations for vent pipes in metal roofs:

– Cut a hole in the roof underlayment so that it is tight to the pipe.

– Cut a hole slightly smaller that the pipe in the center of a piece of 12″ x12″ peel & stick, and pull it down onto the underlayment to seal. Caulk around where the pipe meets the membrane.

– Cut a hole in the metal panel slightly larger than the pipe to accommodate some movement. Install the metal roof panel and caulk around where the pipe meets the panel.

– Lay a bead of caulking around the pipe slightly above where the top of the roof boot will sit on the pipe. Caulk the flange of the roof boot, and pull it down onto the pipe so that it beds in the caulk on the pipe.

– Install the gasketed fasteners on the boot flange.

That gives you a layered approach, with a lot of redundancy if the roof boot fails.