What are the earliest signs of roof damage?

Slates and tiles rarely fail all at once. A nail corrodes, a tail chips, a batten softens, and the component drops a few millimetres. From the ground that reads as a slightly uneven line rather than damage, so it is often noticed only in comparison with the slope next to it.

Where several coverings on the same slope have shifted, the fixings rather than the coverings are usually the subject worth investigating.

Mortar-bedded ridges and verges are traditionally the first details to go. Fine cracking lets water into the bed, frost then opens the crack, and fragments appear in the gutter below. Sand-like grit in a gutter is worth as much attention as a visible gap.

At the same time, a gutter that holds standing water, a valley collecting leaves, or a downpipe staining a wall all create conditions in which minor defects become leaks sooner.

Inside, the earliest evidence is usually a tide mark rather than a drip: darker timber near a valley or chimney, a patch of insulation that has flattened and greyed, or nail heads showing rust. These are records of water that has already been there.

Condensation produces its own pattern, generally spread widely across cold surfaces rather than concentrated in one path, which is why the location of the staining matters as much as its presence.

Early defects are typically isolated, reachable and cheap to correct. Left alone, the same defect wets battens and underlay, then decking or plaster, and the work grows from replacing a component to renewing an area. Nothing about that is inevitable, but the direction of travel is consistent.

That is the honest argument for looking at a roof periodically: not because roofs fail suddenly, but because they usually do not.