The screws work their way out
The ribbed metal on barns, garages and back buildings is held down by thousands of screws driven straight through the panel, each sealing on a small rubber washer. The panel will last decades. The washers will not.
- 1 The ridge cap. On metal it is a separate piece with closures under it. Blown snow finds the joint that was never closed.
- 2 The seams. A standing-seam roof lives at its seams and clips, not at its surface. The panel outlasts what holds it.
- 3 The valley. One channel taking what two slopes shed — and on the north side, holding snow long after the field is clear.
- 4 Where the ell meets the wall. A lower wing dying into the main house. Two roofs, one wall, and nobody sure whose seam it is.
- 5 The fasteners. Exposed screws through the panel, each with a rubber washer. The washers age; the screws work loose.
- 6 The eave. Drip edge, gutter, and the question every metal roof asks: where does a slab of snow go when it lets go?
What actually happens up there
Metal moves. A panel that runs the length of a slope expands and contracts every day the sun hits it, and it does that against a screw that cannot move with it. Over years the hole elongates slightly and the screw loosens. Meanwhile the washer hardens, cracks and stops sealing.
You rarely see either from the ground. What you see is a stain on a ceiling below, or nothing at all until sheathing gives way.
Why this is not a replacement question
A sound panel with tired fasteners is one of the few genuinely cheap fixes left in roofing. The screws come out, oversized replacements with new washers go in, and the roof is good for another long stretch. It is slow work — every fastener on the roof — but it is not a tear-off.
The judgement call is how many are gone and what the holes look like. Past a certain point the panel has been perforated too many times to hold anything, and then replacement is the honest answer. A contractor who will tell you which side of that line you are on is worth listening to.
What to ask
Ask whether the fasteners are being replaced with the same size or a larger one — the same size back into an elongated hole does nothing. Ask what the washers are made of. And ask about the laps and the closures at the same time, because a crew is on the roof anyway and those are the other two places the water gets in.