Parapets, scuppers and where the water leaves
On a pitched roof, water leaves at the edge and nobody thinks about it. On the flat roofs that cover a large share of this region’s housing, the water has to be told where to go — and the places it is told are the places the roof gives way.
Three ways water gets off a flat roof
Over the edge, where the membrane simply runs to a drip edge — the simplest and the least common on this housing type. Through a scupper, an opening cut through the parapet wall that lets water out to a downspout. Or down an internal drain set into the field of the roof and piped through the building. Each has its own failure, and each has to be part of the quote by name.
Scuppers block. Internal drains block and then leak at the joint where they pass through the assembly, which puts water inside the structure rather than on it. And the parapet itself — the low wall the membrane turns up against — is a junction that has to be flashed and capped, which is exactly the sort of detail a fast quote treats as included without pricing it.
Why the new roof fails like the old one
Because a membrane is laid on the drainage that exists. If the slope has settled toward a low spot away from the outlet, the new roof ponds where the old one ponded. If the scupper is undersized for the area it serves, it will back up in the same rain. Correcting drainage means tapered insulation, a new outlet, or both — real work with a real number, and the reason two quotes on the same flat roof can be far apart while both look complete.
The practical test costs nothing: look at the roof two days after heavy rain. Standing water is not a cosmetic issue, it is the drainage telling you what the next roof needs.