Roofs almost never fail overnight. They send signals for years first — and the owners who read them get to plan a replacement on their own schedule, in good weather, at a considered price, instead of commissioning one in a January emergency. Here's what to look for, in ascending order of effort.
From the street
Binoculars, five minutes: tiles slipping repeatedly, in different places each season — fixings failing wholesale, not bad luck. Surfaces spalling or shedding — faces popping off tiles, gravel of tile surface in the gutters. A wavy ridge or verge line shedding mortar. Heavy, spreading moss on ageing concrete tiles — a symptom of porous surfaces as much as a problem itself (see moss on your roof). Any one alone is a repair; several together are a trend.
From the loft
The loft tells the truth the street can't: daylight at the eaves or through the slopes; underfelt that's brittle, torn or crumbling to the touch (the definitive sign — see felt and membrane replacement); water staining on rafters in multiple places; fallen nail heads or tile nibs on the insulation. Brittle felt across the roof is, on its own, enough — everything else ages with it.
From your receipts
The least poetic signal is the most reliable: a repair every winter, each in a new place. That's a covering telling you it's done, one invoice at a time. Our repair-or-replace guide covers the arithmetic properly.
What to do with the signals
Not panic — plan. A roof showing three of these signs often has a couple of years of managed decline left, which is exactly the window to get a proper inspection, an honest verdict and a re-roofing quotation you can schedule on your terms. The worst outcome isn't replacing a roof; it's replacing it in a hurry.