Repair or replace? How to tell when a roof has had enough

This is the question behind most roofing quotes, and the one where homeowners are most often steered wrong in both directions — sold a full re-roof they did not need, or sold another year of patching on a roof that was finished.

The decision is not really about age. It is about whether the parts of the roof you cannot see are still doing their job.

A roof is four things, not one

What people call the roof is a stack: the structure, then a membrane or felt, then battens, then the covering on top. Repairs deal with the covering. Replacement deals with everything under it.

That is the whole test. If the covering has failed in places but the layers underneath are sound, repair. If the layers underneath have gone, no amount of work on the covering will help, because you are fixing the only part that still works.

Signs it is still a repair

• Damage is localised — a handful of tiles, one valley, one flashing
• The rest of the slope looks even and regular from the street
• Battens and felt look sound where the covering has been lifted
• No repeat leaks in the same place across successive years
• The problem appeared after an identifiable event, like a storm

Signs it is heading for replacement

• Slates slipping across the whole roof rather than in one spot — often nail fatigue, where the fixings corrode away while the slate is still good
• Felt visibly perished or missing at the eaves, so wind-driven rain has nothing behind the covering to stop it
• Battens that crumble or give when a tile is lifted
• Visible sagging or dishing between rafters when seen from across the road
• Three or four separate repairs to the same roof in a single year

Nail fatigue is the classic case in older British housing. A Victorian slate roof can have slates in perfectly good condition held on by nails that have quietly rusted through. Refixing individual slates buys a season; the roof is telling you the fixings have reached the end.

The arithmetic that actually decides it

Set the cost of the repair against how long it will last, and compare that to a re-roof against how long that will last. A repair that holds for ten years on an otherwise sound roof is excellent value. The same repair on a roof with perished felt, which you will be back to in eighteen months, is not — and three of those in a row will usually cost more than doing the job once.

That is why repeat repairs matter more than age. A hundred-year-old slate roof that has needed nothing for a decade is in better shape than a thirty-year-old one you have paid for three times since 2024.

How to get an honest answer

Ask to be shown. Any roofer recommending a full re-roof should be able to point at the specific reason — the perished felt, the failed battens, the pattern of slipping — rather than talking generally about the roof's age. A drone inspection makes that straightforward, because you get to look at the same images they are looking at.

And if the survey says repairs will do, that is a perfectly good outcome. Not every roof inspection needs to end in a big job.