Clogged valleys and gutters
A great many reported roof leaks turn out to be a valley that has been holding wet leaf litter for two seasons. The roofing is fine. The water simply has nowhere to go.
- 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.
Valleys carry the most water
A valley is where two roof planes meet, and it collects the runoff from both. It is the highest-volume path on the roof and the one least tolerant of obstruction. Debris packs in, holds moisture against the shingle, and forces water sideways under the courses on either side.
Gutters push water into the wrong place
A blocked gutter overflows backwards under the eave as readily as it overflows over the front. That soaks the fascia, the soffit and the ends of the rafters the roof sits on, rot that is expensive precisely because it is structural rather than cosmetic. And what does come over the front lands against the foundation instead of being carried away.
Old canopy, old suburbs
The postwar neighborhoods across this region, Annandale, Towson, Catonsville, Arlington, were planted when they were built, and that canopy is now seventy years old and overhanging. Roofs under mature trees need their valleys and gutters cleared on a schedule that roofs on open lots do not, and a north slope that never dries grows moss which holds moisture against the shingle.
Two things this region does to a gutter
The first is a spring problem that gets less attention than autumn does. Oaks and tulip poplars dominate the older suburbs on both sides of the river, and in April they drop tassels and seed by the pound: a fine, stringy material that mats rather than piles. That is the thing to weigh before buying guards, because a mesh fine enough to stop it tends to clog on its surface instead, while a reverse-curve design passes it straight through into the trough underneath. Guards are not a decision made once. They are a decision about which season you would rather be up there for.
The second is what happens where the downspout ends. A large share of houses here have finished basements, and the runoff leaving the roof is the same water that arrives at the foundation wall, the window well and the areaway outside a basement door. A gutter overflowing at the eave, or a downspout discharging against the wall, puts it there every time it rains, quietly, for years, and the repair that eventually follows is not on the roof at all. Extensions are cheap and checking where yours end takes no ladder at all.