What kind of vent boot does a metal roof need?
Short answer. Metal roofs use flexible pipe boots with a soft aluminum or rubber base that can be molded to the panel's ribs and a collar of EPDM or silicone sized to the pipe. The base is bedded in sealant or butyl tape and fastened with sealing screws, ideally on the flat of the panel away from ribs and side laps.
How metal roof boots differ
A shingle roof boot slides under the courses above it. Metal panels run in one piece from eave to ridge, so the boot sits on top of the panel and seals to it. The base must conform to the panel's shape so there are no gaps for water to run under.
Choosing the boot
- Size: boots cover ranges of pipe sizes; trim the collar to the right ring for a snug fit.
- Collar material: EPDM for ordinary plumbing vents; high temperature silicone for warm pipes, following the maker's temperature limits.
- Base: a pliable aluminum reinforced base that you shape by hand to the ribs.
- Retrofit boots: split boots that wrap around a pipe when the top cannot be reached.
Placement
- On the flat of the panel when possible, not on a rib or seam.
- Away from panel side laps and end laps.
- On standing seam roofs, large penetrations near the middle of a long panel may need a diverter on the uphill side so water flows around them.
Installation
- Clean the panel, then shape the base to the ribs.
- Apply sealant or butyl tape under the base.
- Fasten with screws that have sealing washers, spaced per the boot maker.
- Seal the top of the collar if the instructions call for it.
Gas flues
Water heater and furnace flues need flue rated flashing and clearances, not a plumbing boot. See metal roofing in Georgia and pipe boot leaks.