Only seven Morris County towns sit outside the Highlands. Everywhere else, from Jefferson and Mount Olive to Morristown and Mendham, falls in the State Climatologist's Northern Zone, with 40 to 50 inches of snow in an average winter. When warmth from the attic melts the underside of that snow, the water runs down to the colder overhang and can freeze there into a ridge of ice.
Age cuts the other way. Riverdale's median house is from 1996 and Mount Arlington's from 1990. A house built in the late 1980s or 1990s may still have its first roof, and shingles that old are often near the end. Chatham Borough, at 1951, and Dover, at 1954, are another story. Those roofs have usually been redone before, and the next crew has to find out how.
Dark stains on the attic boards just above the eaves tell us water has been getting in at the edge. We look up there before anyone talks about shingle colors.
From the road, a 1996 roof and a 1951 roof can look about the same. We climb up when it is safe, check the attic, and only then put a number on paper.