Roof penetration flashings: vent stacks, pipes, curbs, chimneys, skylights and equipment supports
Penetration flashings must keep water out at the roof-to-pipe or roof-to-curb junction while allowing movement, maintenance and drainage. The exam tests curb height, flange embedment, counterflashing and cricket details.
Core rules
- Curbs for skylights, vents and equipment should be raised above the finished roof and membrane; commonly at least 8 in. above the roof surface, or per code/manufacturer. The flange must be wide enough to embed in the membrane or be stripped in.
- Pipe flashings need a flexible boot or metal collar matched to pipe diameter and temperature. On profiled roofs, match the profile and seal the high side.
- Masonry chimneys need base flashing, counterflashing in a reglet, a cap and, where wide, a cricket. A common trigger is a chimney wider than 30 in. parallel to the ridge; confirm code.
- Equipment supports should be curbed, not set directly on the membrane. Use sleepers and flashing that allow service access.
- Counterflashing must overlap base flashing and be removable where maintenance requires.
Worked example
A 42-in.-wide masonry chimney penetrates a low-slope roof with its long side parallel to the ridge. The roofer installs base flashing and a reglet counterflashing but no cricket. That is a defect in most code and manufacturer details: a chimney wider than 30 in. needs a cricket to divert water around the upslope side. Add a cricket, extend base flashing over the cricket, and counterflash both chimney and cricket. Verify the 30-in. threshold in the adopted code, because dimensions and exceptions vary.
Traps
Setting a curb too low; relying on sealant alone at a pipe; omitting a storm collar; flashing a chimney without a cricket; making counterflashing non-removable; ignoring roof slope and shingle/panel profile.