Flashings, Penetrations, and Waterproofing Details
Sidewalls and headwalls
Step flashing is the backbone of tile sidewall details: each piece turns at least 4 in. up the wall and 4 in. onto the roof, laps the next piece by about 2 in., and is installed with every course so the tile and flashing interlock. Counterflashing must overlap the step flashing by at least 3 in. and be secured in a reglet or surface-mounted with a sealed fastener line. Headwalls get apron flashing plus a backer or cricket. A chimney wider than 30 in. requires a cricket under the International Residential Code to divert water around it.
Valleys and penetrations
- Valley metal at least 24 in. wide, 26 gauge or heavier, corrosion resistant, set on top of the underlayment.
- Tiles are held back from the valley centerline so the metal stays open; a swept or closed valley should follow the manufacturer's written detail.
- Keep fasteners roughly 6 in. back from the valley centerline so water cannot follow a nail into the deck.
- Pipe penetrations use a lead or EPDM boot with a secondary pan where required; sealant alone is not flashing.
- Kick-out flashing is required where a wall terminates at an eave or gutter line to keep water out of the wall.
Install every flashing in shingle fashion so water sheds over the top of each piece rather than behind it, and lap the weather-resistive barrier over the wall leg.
Worked example. A 48 in. wide masonry chimney on a 6:12 roof: build a cricket on the upslope side, install pan or backer flashing at the headwall and along the sides, step flash both sides, counterflash the masonry, and confirm the tile sits on the flashing legs, not on the sealant.
Traps. Relying on caulk for a penetration; skipping step flashing and using one long L-flashing; nailing through the valley center; forgetting the kick-out flashing.