Roofs leak at junctions
The field of a roof — the open expanse of shingles or membrane — is the part least likely to fail. Water gets in where the roof stops being a simple surface: where it meets a wall, where two slopes meet, where a pipe or a chimney comes through, and at the edges. Those junctions are handled by flashing, and flashing is where the overwhelming majority of leaks we are called out to actually originate.
What flashing is, and what it is not
Flashing is formed sheet metal, shaped and layered so that water running down the roof passes over the top of every joint and continues on its way. It works through geometry and gravity. It does not depend on anything sticking to anything else, which is why it lasts as long as the metal does. Sealant is not flashing. Sealant is a maintenance material with a service life of a few years, it becomes brittle with UV exposure and thermal movement, and when it fails it does so invisibly under a layer that looks solid.
The pieces, and what each one does
There is a vocabulary here that is worth knowing when you are reading an estimate.
- Step flashing — individual pieces woven into the shingle courses where a slope meets a wall, one per course
- Counter flashing — the piece over the step flashing, let into the wall or masonry, that stops water getting behind
- Kick-out flashing — the small piece at the bottom of a wall junction that throws run-off clear into the gutter
- Valley flashing — the treatment where two slopes meet and concentrate the flow of both
- Drip edge — metal at eaves and rakes carrying run-off into the gutter rather than behind it
- Pipe boots — the collar sealing around a plumbing vent penetration
- Chimney flashing — step and counter flashing around all four sides, with a sound crown above
The kick-out is the one that gets left out
If there is one detail worth knowing about as a homeowner, it is this one. Where a roof slope runs down alongside a wall and ends — at the bottom of a dormer, at the end of an addition — the water that has been travelling down that junction has to be thrown clear into the gutter. The kick-out is a small piece of angled flashing that does exactly that. Without it, the water simply carries on and runs down behind the siding instead. Nothing appears on the ceiling. The wall sheathing behind the siding gets wet on every rain, for years, and the damage is discovered when someone eventually opens the wall up. It costs very little to fit and is omitted constantly.
Why existing flashing fails
Flashing that was installed correctly generally fails for one of a few reasons, and most of them are about time and movement.
- It was never flashing — sealant was used instead, and has reached the end of its short life
- The metal corroded, which happens faster near tidal water and fastest at cut edges
- Differential movement between roof and wall worked the joint open over many seasons
- A previous re-roof laid new shingles over old flashing rather than renewing it
- Masonry above it deteriorated — failed pointing or a cracked chimney crown lets water in above the flashing entirely
- Someone sealed over a defect rather than correcting it, trapping water behind the repair
The re-roof shortcut
Flashing should be replaced when a roof is replaced. It is one of the easiest things to skip, because new shingles laid up to old flashing look perfectly fine from the ground on the day the job finishes. The old metal is then a decade or two older than the roof protecting it, and it becomes the weak point of an otherwise new assembly. If you are comparing estimates, whether flashing renewal is included is a fair and revealing question to ask.
Where this bites in Atlantic County
Two situations locally make flashing more consequential than average. On the barrier islands and along the shore corridor, marine air corrodes metal faster, so flashing has a genuinely shorter service life and material selection matters. Across the county generally, decades of additions — sunrooms, extended kitchens, dormers, enclosed porches — have created large numbers of roof-to-wall junctions, and on work done twenty or thirty years ago those junctions are now the oldest and weakest part of the roof.
