Install Dektite Aluminium properly with this step by step guide. All homes have plumbing vent pipes on the roof. Each vent pipe exits the roof through a hole cut into the plywood substrate under your roof’s shingles. If a plumbing vent pipe is not sealed properly, rain and snow melt will seep around the pipe and into your home. Most vent pipes are sealed with aluminum flashing and a tight-fitting rubber gasket.