On the outside, the result is a common and easy pipe penetration through the exposed-fastener metal roof.
The author then installs a flexible boot (this one is made by Oatey), which has a soft aluminum and lead edge made to conform to the panel ribs (13). (For more on the installation of this type of boot, see the author’s article “Reroofing With Exposed-Fastener Metal Panels,” Sep/20.)
The final steps address two concerns: vermin and water entering the exhaust pipe. To combat vermin, the author uses a PVC mesh insert , which he buys online for around $9.
To prevent water from entering the exhaust pipe, he connects two 90-degree elbows together and attaches them to the exposed PVC stack. He keeps the outlets high enough to prevent snow from blocking them. In areas with more snowfall, they can be made higher, though in practice, the exhaust typically melts snow away from most roof vents before it can cause problems.