Valleys under old trees
The tree canopy is one of the reasons people live in these towns, and it is hard on roofs. A valley is the busiest part of any roof, it carries the runoff of two slopes through a single channel, and under a mature oak it spends half the year holding a wet mat of leaves instead of moving water.
- 1 Ridge caps. Thin, fully exposed, and usually the first course to let go.
- 2 The field. Slate on the older rows, shingle on the rest, each on its own clock.
- 3 Valleys. Two slopes emptying through one line, with litter holding the water there.
- 4 Flashing. Old masonry, and the party wall a rowhouse shares with the house next door.
- 5 The vent boot. A small rubber part with a far shorter life than the roof it sits in.
- 6 Eaves. Where the porch roof ties into the wall, and where backed-up water gets in.
What a leaf mat does
Debris slows water, and slow water is the enemy of every roofing assembly. Shingles in a packed valley stay damp for weeks after a rain; the metal beneath corrodes years ahead of schedule; and through the freeze-thaw cycles of a mid-Atlantic winter, the mat holds moisture against the joint while it freezes and expands. None of this is visible from the ground once the debris settles in, which is why valley condition is the single most reliable indicator of how a treed-lot roof is really doing.
The gutters fail the same way and land the water in a worse place: over the edge, down the fascia, and against the first inches of roof deck. On the older housing here, that is often how a rot problem at the eave begins.
The rhythm, and the quote line
Under a real canopy, one gutter cleaning a year is a gesture rather than a schedule: clear valleys and gutters after the autumn drop, and check again in midwinter. On a replacement, ask specifically what the quote assumes about valley metal. On roofs that have carried leaf load for thirty or forty years it is frequently gone, and a bid that assumes it will be reused has a change order waiting inside it.