In Trenton, 43 percent of homes are attached houses, and only 16 percent stand by themselves. Many of those roofs run straight into the roof next door. On a house that old there may be two layers of shingles, and under them, board decking instead of plywood.
Attached houses are not only a city thing here. Robbinsville's median house dates to 1992, and 27 percent of its homes are attached. East Windsor is at 23 percent. Countywide it is about one home in five, roughly twice the state share. New Jersey's permit exemption for a new roof covers only detached one- and two-family houses, so these roofs go through the town's construction office, and many of them belong to an association.
Plenty of houses from the late 1980s and 1990s are on their original roof, and shingles that old are often close to done. Summer is part of the reason. Central New Jersey sees 15 to 20 days a year above 90 degrees, and a dark roof in full sun gets far hotter than the air around it.
So a Mercer County roof gets priced from on top of it. We go up when it is safe to, count the layers, check the attic, and look at where your roof meets the next one.