The rear porch stack
Nearly every three-decker in this region has a stack of open porches running up the back, one to each floor. The top one carries a roof. It is smaller than the main roof, it is usually older, and it is the single most commonly omitted item in a local quote.
- 1 Ridge caps. The thinnest pieces up there, and the first to work loose over a hard winter.
- 2 The field. Slate on the older stock, shingle on the rest. They age on very different clocks.
- 3 Valleys. Leaf litter mats in them, and two slopes then drain through one line.
- 4 Flashing. Old masonry chimneys, and the porch roof that meets the wall three stories up.
- 5 The vent boot. Rubber that hardens and splits well ahead of the covering it sits in.
- 6 Eaves and ice dams. Where meltwater refreezes at the cold edge and backs up under the courses.
A separate roof on a separate clock
The porch roof is its own assembly: a small, low-slope surface tied into the main structure along one edge, often re-covered independently over the years and frequently in a material chosen for convenience rather than slope. It ages on its own schedule, and because it is out of sight from the street, it ages without anyone looking at it.
Where it fails is the tie-in. The junction between a low-slope porch roof and the wall or main roof behind it has to be flashed properly, and on a house this old that flashing has typically been sealed over more than once. Water getting past it does not appear on the porch. It runs into the wall, and shows up as a stain on an interior ceiling a floor below.
What to ask before signing
Is the rear porch roof included, and in what material? Those two questions separate a complete quote from a partial one on this housing type. A bidder who priced only the main roof is not being dishonest, they may have quoted exactly what they walked, but you will be paying for the porch separately, later, at a price nobody competed for.
The second question worth asking: how does the porch roof tie into the wall, and is that flashing being replaced or sealed? On a stack that has been patched for decades, sealing again is buying a season.