What kind of pipe boot works on a steel roof?
Short answer. Use a flexible EPDM or silicone boot with a formable base made for metal roofing, sealed with butyl tape and fastened with gasketed screws, never a lead boot or copper flashing. Lead and copper react with galvanized and Galvalume steel and corrode the panels, so everything touching a steel roof should be compatible: aluminum, stainless, coated steel or rubber.
Why metal compatibility matters
Galvanized and Galvalume panels are protected by a zinc or aluminum-zinc coating. When wet copper or lead sits against that coating, or rainwater runs off copper onto the steel, the coating corrodes far faster than normal. That rules out lead boots, copper flashing uphill of the panels, and bare steel screws that rust and stain.
Choosing the boot
- EPDM: for plumbing vents and other pipes at ordinary temperatures.
- Silicone: for hot flue pipes, and longer UV life in general. Check the boot's rated temperature against the appliance.
- Base: rubber reinforced with soft aluminum so it can be formed over corrugations or ribs.
- Split retrofit boots: for pipes you cannot remove or cut.
Installing it on corrugated or ribbed panels
- Trim the cone at a ring slightly smaller than the pipe so it stretches snugly.
- Slide it down and form the base to the panel profile.
- Lay butyl tape under the full perimeter of the base.
- Fasten with coated or stainless gasketed screws on a close spacing around the base, as the boot maker specifies.
- Add the top clamp if the boot calls for one.
Placement
Set the base in the flat of the panel, away from laps. A pipe that spans several ribs needs a diverter uphill to send water around it. On homes with steel panels over decking, underlayment beneath the panels is a second line of defense.
See metal roofing in Georgia and pipe boot leaks.