Is torn felt under roof tiles a problem?

Tiles shed most of the rain that hits them, yet a tiled slope is never watertight on its own. Gusts push water up under a tile edge, melting snow can creep backwards, and a cracked tile lets rain straight through. The felt, also called underlay, is the layer laid over the rafters beneath the battens to catch that water and send it down to the gutter. It also keeps dust and draughts out of the loft, which is one reason an old, split sheet makes a house feel colder upstairs.

That makes a torn sheet less urgent than a missing tile, but it also means you may not know it has failed. The tiles can look perfect while the felt beneath is split. The damage often only shows when a gale and heavy rain arrive together and a stain appears on the landing ceiling. By then the timber under the tear has usually been taking water for some time.

Position matters more than size. A short split high on a plain slope, under tiles that are all present and sound, is a low-risk fault that can be watched. A tear in the same felt near the eaves, where all the water on the slope converges, is more serious. So is a tear along a valley, round a chimney, beside a skylight or under the ridge, because these are the places where roofs already struggle to stay dry.

Sagging counts too. Felt that droops between rafters forms a pocket that holds water instead of shedding it, and the weight stretches the sheet until it splits. Felt that has gone brittle, with cracks along the folds, has little service left even before it tears. We note all of this at survey, and the photographs show you which category your roof falls in.

Pick a dry day, take a torch and look up at the underside of the roof, working slowly along each slope. Daylight pinpricks around a tear are easy to see, and so are dark stains on the felt or timber below it. Loose, hanging felt, rodent nibbling, and places where cables or pipes have been pushed through are all common causes. Sometimes a roofer working years earlier has simply left a gap.

Keep to the joists or boarding while you look, and do not pull at the felt or push through it, because loose tiles may sit just above. If you find a wet patch, photograph it and put a bucket under it. Outside, never go onto the tiles to hunt for the cause. Our guide to slipped tiles and insurance covers what to record after storm damage, and why the pictures count.

A patch stuck to the underside from inside the loft is a stop-gap at best. A lasting repair is done from above: the tiles over the damage are lifted, a new strip of felt is fitted so that its upper edge slides under the sheet above and it laps over the one below, and the battens and tiles go back. That way water running down the roof meets an overlap that sheds it, not a seam that holds it.

Where the felt has perished across a whole slope, patching is a false economy and new underlay across that slope is the sensible repair. Ventilation needs attention at the same time. With a high-resistance underlay over a cold roof, Marley gives an eaves ventilation gap of 25mm along the eaves for pitches of 15 degrees or less and 10mm for steeper ones, so new felt must not smother that gap. For more on this, read our guide to underlay and ventilation.

If a recent storm tore the felt and tiles, make the area safe first. Which? says to get in touch with your insurer early, tell them about any emergency repair you arrange yourself, keep the receipts and do not bin damaged items. Photographs of the felt and the tiles help whoever assesses the damage later. We prioritise a roof that is letting water in, starting with a temporary cover to stop the worst of it. The insurer decides what is covered, so check your own policy.

After that, the price comes down to how much felt is involved, how far the tiles have to be lifted and whether any battens have been spoiled by water. Price is settled after the survey, in a written quote that gives one sum. If you would like to see the other jobs that come up on tiled roofs, from small repairs to full re-covering, the pitched roofing page lists them.