How long can natural slate roofing last?

Corroding fixings release slates gradually across a roof. The pattern is characteristic: individual slates slipping in different places over several years, with the covering itself still sound. Each one can be replaced, but the underlying cause continues, so the repairs never end.

Confirming it means lifting a sample slate and looking at the nail, which imagery cannot do. It is the single most important finding on an older slate roof, because it changes the whole economics of repair.

Some slate deteriorates by splitting into layers, showing thin flaking edges, softness, or a dull, powdery surface. Where that is widespread, slates cannot reliably be re-fixed, and the proportion that can be reused falls.

Where it affects only some slates, sorting during a strip and re-lay recovers the sound ones and supplements with matching material.

This is the option most often appropriate on a sound slate roof with failed fixings: slates are carefully removed and sorted, battens and underlay renewed, then the reusable slates re-laid with new fixings and supplemented as needed.

It renews the parts that have actually failed while retaining the material and appearance of the original roof — which also matters where a building is listed or in a conservation area.

Keep valleys, gutters and outlets clear so water is never held against the covering. Deal with slipped slates promptly, because each gap exposes the underlay. Avoid walking on the roof, and avoid pressure washing entirely — both break slate.

Where mortar-bedded ridges and verges are present, watch them: they usually need attention well before the slate does.

Ask for an inspection that reports on fixing condition from a lifted sample, the proportion of slate likely to be reusable, batten and underlay condition, and the state of the details. That is what distinguishes a roof with decades left from one due for strip and re-lay.

It is also the information a quotation should be built on, rather than an assumption about age.