Flashing failure
Ask anyone who repairs roofs where they leak and the answer is the same: not in the middle, but wherever the roof meets something else.
- 1 Ridge caps. Thin, fully exposed, and the first course to lift.
- 2 The field. Granule loss is the honest measure of how much life is left.
- 3 Valleys. One channel taking the runoff of two slopes, all year round.
- 4 Flashing. At the chimney, and where the garage roof meets the wall of the house.
- 5 The vent boot. Small, rubber, and on a much shorter clock than everything around it.
- 6 Eaves. Where water that has backed up at the edge gets under the courses.
Step flashing along a wall
Where a roof plane runs into a wall, most commonly along an attached garage or a second-story addition, individual metal pieces are woven in with each course of shingle. Done properly it is invisible and lasts as long as the roof. Done as a single continuous strip sealed with caulk, it fails within a few years when the caulk cracks.
This is also the item most frequently re-used rather than replaced during a roof replacement, and it is the most common reason a new roof leaks in its first year.
Chimneys
A chimney needs two layers: base flashing that goes under the shingles, and counter-flashing set into a groove cut in the mortar and folded down over the base. Where the counter-flashing has simply been surface-sealed to the brick, it is a matter of time. Older masonry across this region has frequently been repointed at some stage, and the flashing detail does not always survive it.
Vent boots and skylights
The rubber collar around a plumbing vent stack is the shortest-lived component on most roofs. Fifteen to twenty years of ultraviolet exposure cracks it, and water runs straight down the pipe into the ceiling below, often appearing in a bathroom. Skylights leak at their own flashing kits, and a skylight that is older than the roof around it is worth looking at closely.
The addition, and the joint nobody planned for
A great deal of the housing on both sides of the river has been added to: a family room off the back of a rambler, a bumped-out kitchen, a sunroom where a deck used to be, a second story over a garage. Every one of those brought a new roof up against an old wall, and that junction is where a disproportionate share of the leaks in this region actually live. The reason is rarely poor work on the day. It is that the two roofs age on separate clocks, move at separate rates, and were commonly built by different trades a decade or more apart.
What to look at is the transition itself. Whether the newer roof was woven into the old wall with step flashing running up behind the siding or brick, rather than surface-sealed against it. Whether there is a cricket where an addition’s ridge dies into a wall. And whether the change in pitch was handled with the right material, because a shallow addition roof coming off a steep original is a common pairing here, and a shallow roof needs an underlayment and flashing specification that a steep one does not. On an added-on house, the addition line is where an evaluation should spend its time first.
Where two houses share a wall the question changes shape entirely. On the attached and semi-detached blocks through Dundalk and Essex, the joint sits between two roofs that were covered in different decades by different owners, and the party-wall detail belongs to neither of them until it lets go. The split-levels and ranchers further out in Randallstown and Timonium have the gentler version: an addition line where something shallow was tied into a steeper original, usually by a different crew, usually years later.