Roof Repair or Full Re-Roof? How to Decide

Damage confined to one area, one slope or one detail is a repair. Storm damage to a dozen tiles above the back bedroom, a cracked valley, a failed chimney flashing: all of these are straightforward, targeted work on a roof that is otherwise doing its job.

Damage appearing in unrelated places at once is a different signal. Slipped slates on the front and the back, mortar failing at the ridge and both verges, and staining in two corners of the loft together mean the roof is failing as a system rather than at a point.

As a rough rule, if more than about a quarter of the covering or its fixings need attention, replacement becomes the better value answer.

This is the one that decides most cases. Underlay is the secondary barrier that catches anything getting past the tiles, and it cannot be replaced without stripping the roof.

If the membrane is intact and flexible, a repair is genuinely worth doing because the roof still has a backup. If it is brittle, torn, or absent entirely as on many pre-war roofs, then every future fault becomes an indoor leak immediately.

Ten minutes in the loft with a torch answers this. It is the first thing we look at on any repair-or-replace survey.

Divide the price by the years of service you can reasonably expect from it. A £400 repair that buys five good years costs £80 a year. A £7,000 re-roof that buys fifty years costs £140 a year, but with no call-outs, no interior damage and no worry.

Now do the same sum on a roof needing annual attention. £500 a year of repairs on a roof that is going to need replacing in five years anyway means you spend £2,500 and still pay for the new roof.

The maths is not always in favour of replacement. On a sound roof with a decade left, repairs win comfortably. The point is to do the arithmetic rather than guess.

If you plan to be in the house for fifteen years or more, and the roof is marginal, replace it. You will pay for it once and never think about it again.

If you are selling within a year, a well-documented repair plus a written survey report is usually the more rational spend. Buyers rarely pay a premium for a new roof but they do walk away from an unexplained one.

If you are somewhere in between, get both options priced. Seeing them side by side with the expected life of each makes it obvious more often than not.

Some firms offer to fit a new covering over the existing one to save the strip-out cost. On a pitched roof we would generally advise against it. You cannot inspect the deck, you cannot replace the underlay, you add weight, and you inherit whatever was wrong underneath.

On a flat roof it is different. A reinforced liquid overlay on a sound dry substrate is a legitimate, well proven way to extend the life of a roof by twenty years without disruption, and it is standard practice on commercial buildings.

The test is whether you can verify the substrate. If you can, overlay is an option worth pricing. If you cannot, strip it.

There is a middle path people forget: replacing one slope. On many terraces the weather-facing slope has deteriorated years ahead of the sheltered one, and doing that side alone is perfectly legitimate.

It costs more per square metre because the scaffolding and set-up are shared over less area, but it can be far kinder to a budget and it puts the money where the failure actually is.

We will always price the whole roof alongside it so you can see the difference, and we will tell you honestly if the second slope is likely to follow within a couple of years, because in that case doing both now is cheaper.