Step flashing is a series of individual lead or metal pieces that make the junction between a pitched tiled roof and rising masonry watertight — along a chimney, for example, or against a higher gable wall. Each piece is tucked into a bed joint in the masonry and dressed over the tile below, so water is always carried outwards onto the roof surface. In Dutch this component is called a loket.
Because a sloping roof meets a vertical wall, the junction has to follow the pitch. Each piece therefore covers one tile and then steps up one course of brickwork — which is where the familiar staircase pattern on every masonry chimney comes from.
How the junction is built up
- Front apron — at the lower side of the chimney, dressed over the tiles
- Step flashings — down both sides, stepping up tile by tile
- Back gutter and soakers — at the upper side, taking water around the chimney
Each piece has an upstand that goes into the bed joint and is held with lead wedges, after which the joint is repointed or sealed. In UK practice the stepped cover flashing is often combined with separate soakers underneath the tiles.
Rules of thumb for the upstand
The shallower the roof, the higher the flashing must run up the wall, because water drains more slowly and wind drives it further up. As a guide for the number of brick courses the upstand spans:
| Roof pitch | Upstand (indicative) |
|---|---|
| About 30 degrees | 2 courses of brickwork |
| About 45 degrees | 3 courses of brickwork |
| About 60 degrees | 4 courses of brickwork |
Common mistakes
- No open perpends — some seepage and condensation always ends up behind the flashing. Without open perpend joints at the bottom it cannot escape
- Flashing dressed too far over the tile — no more than about a third of the tile; beyond that you get wind-driven water and loose edges
- Sealant instead of a chased joint — mastic alone is not a fixing; the upstand belongs in the joint
- Pieces that are too large — lead expands and contracts. Use individual pieces per tile rather than one long strip, otherwise the lead splits along the fold
Related terms
- Sheet lead
- Roof penetration
- Bed joint
- Perpend joint
- Roof pitch
- Lead replacement flashing
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.