In Perth Amboy, Dunellen and Carteret, about one home in five is a two-family house. Water that gets in above the top unit can follow a wall cavity down and show up in the first floor kitchen. The tenant often sees it before the owner does.
In Monroe Township about one home in four is attached, and in South Brunswick about one in five. On a row of townhouses, the weak spots are where two roofs meet, at a party wall or a change in height. A stain in your unit can come from a gap on the roof beside yours.
Middlesex sits in the middle of the Central Zone, where winter storms often turn from rain to snow and back. Slush packed into a valley or a full gutter freezes overnight and can push water under the bottom row of shingles. Summer is hard on the roof too: in full sun a dark roof runs far hotter than the air, and old vent boots crack.
The stain is where we start, not where we fix. You see photos of the source before any repair.