Salt at the metal
A roof in Revere, along the Lynn shore or out toward Squantum can look sound from the sidewalk and be finished at every junction. The covering is doing fine. The metal holding it together is not, and salt is the reason.
- 1 Ridge caps. The thinnest pieces up there, and the first to work loose over a hard winter.
- 2 The field. Slate on the older stock, shingle on the rest. They age on very different clocks.
- 3 Valleys. Leaf litter mats in them, and two slopes then drain through one line.
- 4 Flashing. Old masonry chimneys, and the porch roof that meets the wall three stories up.
- 5 The vent boot. Rubber that hardens and splits well ahead of the covering it sits in.
- 6 Eaves and ice dams. Where meltwater refreezes at the cold edge and backs up under the courses.
What salt actually attacks
Not the shingles or the membrane, the metal. Step and counter-flashing at walls and chimneys, valley metal, drip edge, fasteners, and the collars around plumbing vents. Airborne salt keeps those surfaces damp longer than they would otherwise be and accelerates corrosion, which means the junctions of a coastal roof are on a shorter clock than its field.
That reverses the usual reading of a roof. Inland, a covering ages across its whole surface and the field tells you where it stands. On the coast, the field can have years left while the flashing has none, and the leak arrives without the visual warning an owner is watching for.
What to specify, and what to refuse
Corrosion-resistant metal, named in the quote rather than assumed. Replaced rather than reused. This is the line where a coastal quote gets cheap, because sealing over existing flashing takes an hour and lasts a season or two. Fasteners chosen for the environment, since a stainless nail costs almost nothing more and outlives the roof. And vent collars replaced as a matter of course rather than inspected and passed, because they are among the first things to go here and cost almost nothing to change while the crew is on the roof.
A useful question for any bidder within a mile of the water: what metal are you using, and is it going in new? A bidder who has worked this shoreline answers immediately.