Freeze-thaw cycling
A Front Range winter day can swing thirty degrees between afternoon and midnight: strong sun warms the roof surface well above freezing, then the temperature drops hard after dark. Every cycle expands and contracts the shingles, the fasteners, the sealant strips and the metal — and the cycles number in the thousands over a covering’s life.
What fatigue looks like on a roof
Movement works fasteners loose: nails back out a fraction at a time until a shingle no longer lies flat, and a raised nail head telegraphs through as a bump before it becomes an opening. The factory sealant strips that bond one course to the next lose their grip the same way, and ridge caps — the thinnest, most exposed pieces on the roof, bent over the peak — are reliably the first to work loose.
Because fatigue is mechanical rather than visible wear, it shows up as small failures scattered across an otherwise reasonable-looking roof. That pattern — loose caps here, a lifted course there — is the signature of cycling, and on an older covering it means the material has stopped being able to hold itself together.