Valleys and flashing: where roofs leak
Shingle Roofs · 6 min read ·
Roofs rarely leak in the open middle of a slope. They leak in valleys, along walls, around skylights and chimneys, which are exactly the places that need extra metal and extra care.
Water concentrates where the roof changes direction
On a plain slope, rain spreads out and runs straight down. Where two slopes meet in a valley, all the water from both sides funnels into one line. Where a roof runs into a wall, water wants to go behind the siding. Those spots carry far more water than the field of the roof.
That is why a good re-roof spends a disproportionate amount of time on the edges and intersections, and why a leak inside the house usually traces back to one of them.
Valleys
A valley is the inside corner where two roof planes meet. On the Onyx Black re-roof in October 2026, the crew cut in new valleys where the roof sections meet as the shingles came up from the eaves.
The hero photo is from that job: a gable section tying into the main roof, the shingles running into the valley line, and the hip caps going on. The last photos from that day show the hips and valleys finished in solid black.
Where a lower roof meets a wall
On the brown shingle flashing job in June 2026, a lower roof runs along the sided walls of the house. That lower roof is where a house like this usually lets water in, so we took our time there.
We ran the brown Owens Corning architectural shingles right up to the siding and set dark metal flashing along every wall line. The flashing carries through the inside corners, behind the downspout and past the window trim, so water has a clean path down and off the roof instead of behind the siding.
Skylights and chimneys
A skylight is a hole in the roof with glass in it, and it needs flashing on all four sides. On the October job we flashed the skylight as the shingle field came up around it, rather than working around it at the end.
Chimneys work the same way. On the brick ranch the shingles were cut in around the brick chimney. Metal roofs need the same attention at a chimney, which our post on chimney flashing on a metal roof covers.
Signs from inside the house
A stain on a ceiling near an outside wall, a damp spot under a skylight, or a wet patch in the attic beside the chimney usually points to one of these leak points rather than the open roof. Note where the stain is and when it shows up, such as heavy rain or snowmelt. It helps narrow things down.
Sometimes the fix is new flashing on one spot. Sometimes the roof around it has aged out and a full re-roof makes more sense. We say which one we see after looking.
Getting it looked at
Send a shingle roof request and mention where the leak shows up inside. We will check the valleys, wall lines, skylights and chimney first, then the rest of the roof.
Siding and roofing meet at these same wall lines, so if the siding is also tired, read signs your siding needs replacing before the visit.
Questions
Where do shingle roofs usually leak?
Shingle roofs usually leak at valleys, where a lower roof meets a wall, around skylights, and around chimneys, rather than in the open middle of a slope. Those spots collect or redirect the most water. Schaub and Sons pays extra attention to valleys, wall flashing, skylight flashing and chimney work on every shingle re-roof.
What is a roof valley?
A roof valley is the inside corner where two roof planes meet, forming a channel that carries water from both slopes down to the eave. Because a valley handles so much water, it is a common leak point. Schaub and Sons cut in new valleys where the roof sections meet on an October 2026 Onyx Black re-roof.
What is step or wall flashing on a shingle roof?
Wall flashing on a shingle roof is metal set along the line where a roof meets a sided wall, so water runs down and off the roof instead of behind the siding. On a June 2026 job, Schaub and Sons set dark metal flashing along every wall line of a lower roof, through the inside corners and behind the downspout.
Does a skylight need new flashing when the roof is replaced?
A skylight should be flashed as part of a re-roof, because the old flashing is tied into the old shingles that are being removed. On an October 2026 re-roof, Schaub and Sons flashed the skylight as the new Owens Corning Duration Onyx Black shingles came up around it, instead of patching around it at the end.
