Where Roof Meets Wall

What proper step flashing is

One piece of metal per shingle course, not a continuous strip.

Each piece lapped over the course below it, so water running down the wall is always directed out onto the shingle.

Turned up the wall far enough, typically well above the shingle surface.

With the wall finish — siding, brick, stucco — or a separate counter flashing lapping over the vertical leg.

Nailed in the correct place so the fastener is not in the water path.

And carried past the bottom of the wall onto a proper kick-out, which diverts the water into the eavestrough rather than into the wall below.

The kick-out is the missed piece

Where a sloped roof meets a wall and ends at the eave, a kick-out flashing at the bottom throws the water clear into the eavestrough. Without it, every drop running down that junction goes behind the wall cladding at that point. It is a small piece of metal and it causes a great deal of hidden wall damage by its absence.

Where it shows up in Toronto

Dormer cheeks, which are the classic case and are on a great many Toronto houses.

The junction between a main roof and a rear addition, which is almost always a retrofit and frequently flashed badly.

A porch or garage roof meeting the house wall.

Semi-detached party wall junctions, where the two roofs meet a shared wall.

Bay window and projection roofs.

And anywhere a lower roof meets a brick wall, where the counter flashing should be cut into a mortar joint and usually is not.

The damage it causes

Wall framing and sheathing rot behind the cladding, invisible from both sides until it is extensive.

Interior staining at the ceiling-to-wall junction below.

Mould in the wall cavity.

Insulation wet and no longer insulating.

On a brick wall, water moving through to the interior face and efflorescence outside.

And a repair scope that reaches well beyond the roof, which is why this junction is worth getting right rather than caulking.