Roof repairs

Finding the leak

The stain on the ceiling is rarely under the hole in the roof. Water gets in at one point, then runs along the underlay, down a batten or along a rafter until it finds somewhere to drop. On a pitched roof that can put the stain a metre or more downslope of the fault, and now and then in a different room altogether.

So tracing starts inside where there is loft access, following the staining on the timbers back uphill, and then moves outside to the likely culprits above that point: a flashing, a valley, a cracked slate, a chimney. Some leaks only show in wind-driven rain from one direction, which is worth mentioning when you call. The aim is to find the cause before anything gets replaced, not to replace things until the drip stops.

Slates, chimneys and flashings

A single slipped or broken slate is a straightforward repair. The replacement is matched to what is on the roof and held with a tingle or a slate hook, since the original nail holes are under the course above and cannot be reached without stripping. Where slates are slipping because the nails have corroded, the repair holds but the next one will not be far behind. That is nail sickness, and it is covered on the roofing page.

A lot of leaks come from where the roof meets something else: a chimney, a party wall, a dormer or an abutment. Those joints are sealed with lead — step and cover flashings down the sides of a stack, soakers under the slates, and a back gutter behind the chimney to carry water round it. Lead that has split or pulled out of its joint, or that was replaced at some point with a mortar fillet, is the usual cause. Fillets crack because the roof and the chimney move at different rates.

Chimney work also takes in repointing the stack, renewing the flaunching that holds the pots, and fitting ventilated caps to flues that are no longer used. On a tall stack that means a scaffold or a chimney platform, not a ladder.

Ridges, valleys and storm damage

Ridges and hips bedded in mortar crack and work loose with age, and once the bedding goes a ridge tile can lift in a strong wind. Loose ridges get rebedded, or replaced with a mechanically fixed dry ridge that does not depend on mortar at all. Valleys carry more water than any other part of the roof and fail in a few predictable ways: lead laid in lengths that are too long splits from expansion, mortar-bedded valley tiles crack, and leaves and moss build up until water backs up over the edge.

After high winds the first job is to get the roof watertight, refixing what has come off or putting a temporary covering on if the full repair has to wait for materials or a dry day. If you are claiming on insurance, photograph the damage before anything is moved. Wind tends to find a roof’s existing weak points, so a run of slates gone along one verge or a ridge lifted in one piece often says more about old fixings than about the storm.

When repair stops making sense

Most roofs are worth repairing, and a sound roof with one bad flashing does not need replacing. The picture changes when the same roof keeps needing attention. Slates slipping across several slopes, underlay that has perished or was never there, battens soft enough to push a screwdriver into, ridges and valleys all reaching the end at once: those are signs that the roof as a whole has worn out, not one part of it.

At that point each repair is money spent on a roof that will need replacing anyway, and none of it carries over to the new one. If that is where your roof is, you will be told, with the reasons and photographs, and you can have a price for both so the comparison is in front of you. If it only needs a repair, it will be quoted as a repair. There is more on what replacement involves on the new roofs page.