Solar panels on a roof that is running out of time
Rooftop solar arrived across Maryland and Virginia in volume, and a great many arrays went onto roofs that were already halfway through their lives. Panels are warranted for decades. The covering beneath them is not, and nothing about having an array up there slows the shingle down. Sooner or later the two schedules collide, and the homeowner discovers that the roof under the panels is the complicated part.
- 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.
Two clocks that rarely line up
An array is designed to sit undisturbed for twenty-five years or more. An asphalt roof in this climate is doing well to reach twenty. If the panels went on when the roof was already ten, the arithmetic is settled before anyone thinks about it: the covering will need replacing while the array is barely middle-aged, and the array has to come off and go back on for that to happen. Nothing has gone wrong. It is two products with different service lives fastened to each other.
The moment to check is before signing for an array, and the question is short: how much life is left in this roof, and is it more than the panels are expecting. Where that conversation did not happen, the useful thing is to find the answer now, on a dry afternoon, rather than at the point a ceiling starts marking.
What the mounts do to the roof
Most residential arrays are held down by feet lagged into the rafters, and every foot is a hole through the deck. Done properly, each one is flashed the way any penetration is flashed, with a metal plate woven under the course above it so the water goes over the top and keeps moving. Done quickly, it is a lag bolt and a bead of sealant, and sealant is a consumable rather than a detail. There are a good many of these on a typical roof, so it is worth knowing which method is on yours; the installer’s own documentation generally says.
There is also the part of the roof you can no longer look at. Panels shade what is under them, which slows some kinds of aging and encourages others, and they make the field beneath effectively unreadable without taking them off. A roof carrying an array should have its accessible planes and its attic read that much more carefully, because that is the evidence still available.
Removal and reinstallation is its own job
When the roof does come off, the array comes off first and goes back last, and that is a separate scope with its own trade: the electrical disconnection and reconnection, the racking, and the old mount holes, which have to be properly closed rather than simply covered over by the new courses. Whether your solar agreement contemplates any of this, and who holds the warranty on the array once a second company has handled it, are questions to settle in writing before a date is set, not while the roof is open and everyone is standing in the driveway.
The sequence that avoids all of it
If a roof is anywhere into the second half of its life, the order is replace first, install second. A new covering under a new array gives the pair a matched start and takes the whole question off the table for two decades. Where the array is already up and the roof is aging, the thing that helps is an evaluation that grades the planes it can reach, reads the deck from inside the attic, and puts a realistic window on the covering. That turns an open-ended worry into a date you can plan around, which is a considerably better position than finding out through a stain on a bedroom ceiling.
The two clocks are furthest apart where the houses went up together and the panels arrived later. Across the Northern Virginia developments (Sterling, Centreville, Woodbridge, Manassas), a whole street was often covered in one season, then had arrays added most of a decade afterwards. That gap is the decision: the panels are barely used and the covering beneath them is not.