A shingle roof is good at one thing: shedding water downhill across an unbroken surface. Most leaks on pitched roofs start where that surface is interrupted, by a chimney, a skylight, a plumbing vent, an exhaust fan, a wall or a valley. On Edison's older houses, with brick chimneys and skylights added in the 1980s, those interruptions cause far more calls than worn-out shingles do.
Chimneys
Brick chimneys need two kinds of metal to stay dry where they pass through the roof: step flashing woven into the shingles along the sides, and counter flashing set into the mortar joints and lapped over it. Wide chimneys also need a small peaked cricket on the uphill side to split the water around them.
What usually goes wrong: flashing that was only caulked or tarred instead of properly stepped, counter flashing that's pulled out of crumbling mortar, or a missing cricket behind a wide chimney. What you see is a stain on the ceiling or wall next to the chimney, often worst in wind-driven rain. What happens next is usually new flashing, sometimes with mortar repair; a chimney in poor shape may need a mason's attention too.
Skylights
Skylights leak in two ways: through their own seals and glass, or around their frame where they meet the roof. Many skylights in Edison homes were added years after the house was built, sometimes without the manufacturer's flashing kit.
What usually goes wrong: old flashing, failing seals on aging units, or condensation that looks like a leak. What happens next is reflashing, or replacing the skylight, which is easiest during a reroof.
Vent Pipes and Exhaust Vents
Plumbing vent pipes come through the roof with a pipe boot: a metal or plastic flange with a rubber collar around the pipe. The rubber cracks after years of sun.
What you see is a small stain on a ceiling under a bathroom or kitchen, or a damp spot around the pipe in the attic. What happens next is usually a new boot, a small repair if the shingles around it are still in good shape.
Bathroom and kitchen exhaust vents, roof vents and attic fans have their own flashing and can leak the same way.
Walls and Dormers
Where a roof runs into a wall, such as a second-story wall on a split-level or the side of a dormer, step flashing has to tuck behind the siding. If it's short, missing or covered over by later siding work, water gets behind the siding and into the wall.
Valleys
Valleys carry water from two roof planes, and they collect leaves and ice. An open metal valley or a properly woven shingle valley, with ice barrier underneath, holds up best.
Why the Stain Isn't Always Below the Leak
Water that gets past flashing runs along the underlayment, the decking or a rafter before it drips. The stain on the ceiling can be several feet downhill from the actual entry point. That's why a roofer checks from the attic as well as from the roof.
Gutters and Drip Edge
Not every leak at the edge of a roof is a roofing failure. Gutters that are clogged, pitched the wrong way or pulling away from the fascia can overflow behind themselves and soak the fascia board and the top of the wall. A missing or short drip edge lets water curl back under the shingles at the eaves. What you see is staining at the top of an exterior wall or rot along the fascia. What happens next is usually a drip edge or flashing correction during a repair or reroof, and getting the gutters working again.
Questions
Can a chimney leak be fixed with sealant?
Sealant can stop it for a season. A lasting fix is proper step and counter flashing.
Should I replace skylights when I replace the roof?
If they're as old as the roof, it's usually the best time, because replacing them later means opening the new roof around them.
How long do pipe boots last?
Rubber collars commonly crack within 10 to 15 years, often before the shingles around them wear out.
Around Edison
Chimney and dormer leaks are common on older roofs in Metuchen and Stelton, and skylight leaks on colonials in East Brunswick. Repairs are covered on roof leak and storm repair.
Attic Ventilation and Ice Dams on Low-Slope Ranches
Why icicles form, and what actually stops them.
How Long a Roof Lasts in Central New Jersey
Lifespans by material, and what shortens them.