Where the back wing meets the house
Almost nothing here was built in one go. There is the house, and then there is what was added behind it — a kitchen wing, a back room, a porch that was enclosed one winter. Where that lower roof runs into the main wall is where the water gets in.
- 1 The ridge cap. On metal it is a separate piece with closures under it. Blown snow finds the joint that was never closed.
- 2 The seams. A standing-seam roof lives at its seams and clips, not at its surface. The panel outlasts what holds it.
- 3 The valley. One channel taking what two slopes shed — and on the north side, holding snow long after the field is clear.
- 4 Where the ell meets the wall. A lower wing dying into the main house. Two roofs, one wall, and nobody sure whose seam it is.
- 5 The fasteners. Exposed screws through the panel, each with a rubber washer. The washers age; the screws work loose.
- 6 The eave. Drip edge, gutter, and the question every metal roof asks: where does a slab of snow go when it lets go?
Why the junction is hard
A roof that ends against a wall cannot simply be sealed to it. Water running down the wall has to be caught above the junction and directed out onto the lower roof, which means metal worked into the wall itself and lapped over the covering below. Done properly it outlives everything around it.
Done as a bead of sealant along the joint, it lasts a few seasons. Sealant under this freeze cycle is a maintenance item, not a detail, and it is the single most common thing found behind a stain on a back-room ceiling.
The complication nobody owns
These junctions sit exactly between two trades. The wall is masonry or siding; the roof is roofing. On an older brick or stone wall the counterflashing has to be let into a joint and pointed back in, which is masonry work done by a roofer, and plenty of crews will simply surface-mount it and move on.
Ask specifically: is the counterflashing being let into the wall, or fastened to the face of it? The two answers are a few hundred dollars apart and a decade apart.
And the pitch changes too
A wing added behind a steep house is almost always shallower — sometimes much shallower. Water leaves it slowly, snow sits on it longer, and it frequently needs a different product from the front slope entirely.
One specification for the whole property under-serves that back roof, and the back roof is the one that fails. It should appear as its own line in the quote.