Dormers, chimneys and the leaks that follow
On a complicated roof, leaks rarely come from the middle of a flat shingle field. They begin at the details: step flashing along dormer walls, counterflashing at chimneys, valleys where two slopes meet, and the points where porches join the main roof. Worn sealant and rusted metal give way first.
Winter is hard on these spots. Snow piles in valleys, ice forms at cold eaves and the freeze and thaw cycle opens small gaps. Mature trees around older homes shed leaves and limbs, which block valleys and wear surfaces. Careful repair of flashing is often more effective than replacing shingles, and a full replacement should include new flashing instead of reusing worn pieces.
