Snow, wind and shade on Brooklyn roofs
Brooklyn is rolling farmland broken up by woodlots, so a roof's exposure depends on which side of the house you look at. Fields leave the west and north slopes open to winter wind, which lifts shingle tabs and drives rain under ridge caps. Tree lines on the east and south drop leaves into valleys and gutters, and shaded slopes stay wet enough for moss. Snow is heavier here than in the valley towns and lingers on cold roofs, so ice forms at the eaves of old houses and at the bottom of long rear saltbox slopes. Repeated freezing and thawing through March loosens flashing and opens nail heads.

