The short answer
Torn roof felt means the secondary waterproof layer under your tiles has failed in that spot. A small, isolated tear on an otherwise sound roof can often be patched from above when tiles are lifted. Widespread tearing, brittle felt, or sagging that holds water points to an ageing underlay, and then the tiles have to come off so new felt can go down properly.
What the felt does, and why you can see it
Under the tiles or slates on most pitched roofs sits a sheet material, laid across the rafters and held down by the battens. Roofers call it underlay or felt. Its job is secondary: the tiles shed nearly all the rain, and the felt catches what wind-driven spray, snow dust or a cracked tile lets through, and drains it down to the gutter.
In a loft with no ceiling boards under the rafters, you look straight at the underside of that layer. That is why a torn piece is so visible: a ragged hole, a flap hanging down, a ripple in the middle of a bay or a length curling away at the eaves. Old bitumen felt turns brittle, and a modern breathable membrane can tear if it is caught by a nail or pulled when the roof was laid.
We cover what the layer is made of in our roof underlay guide.
Why felt tears or sags
Age is the common cause. Bitumen felt, especially the old hessian-based kind sometimes found under older houses, dries out over decades of loft heat and cold. It cracks along the line of every batten, and a finger pushed against it turns into dust.
Other causes are mechanical. Someone has walked in the loft and pushed a foot through. A tile has slipped and a loose nail rubbed a hole. Birds or squirrels have torn at it to get in. Fitters running cables or pipes cut the felt and left it hanging.
Sagging has its own reasons. If the felt was laid too tight, it can pull away from the battens. If it was laid with too much slack, it can pool water behind a tile, and the pool then sits on the batten and rots it. Light patches in the loft, where you can see daylight, signal a hole. A sag that feels damp, or a batten that crumbles under pressure, means the felt has been doing more work than it should.
When a patch is the right answer
A repair works when the damage is small, the felt around it is still flexible and the battens and tiles are in good order. For instance, a single tear caused by a slipped tile on a roof otherwise in good condition can be fixed from outside. The roofer lifts the tiles in that area, slides a new strip of underlay up under the existing sheet, and lays it so the upper layer overlaps the lower, which keeps the water running over the joints and not into them. The tiles are then relaid.
A patch is not suited to felt that is brittle everywhere. New material stuck to old rarely holds, and the next tear appears a short distance away.
Do not try to tape or glue a tear from inside the loft. It looks like a fix, but it hides a fault and gives no waterproofing, since rain arrives from above and runs behind it.
When torn felt points to a re-roof
Replacing underlay across a whole slope means taking the covering off and putting it back, so it is a re-roof in all but name. That is the route when the felt is torn in several places, crumbles to the touch, or has sagged along the roof. At that point the tiles are the part that still works, and the underlay is the part that has gone.
The position often justifies it. If the battens are soft or rotted, new felt on bad timber is wasted effort, and our page on rotten roof battens explains how we judge them. If the tiles are also near the end of their life, a full re-cover with new underlay and battens is the sounder choice.
Re-covering a roof can bring Building Regulations into play. Where the work stays under 25 per cent of the total building envelope and under 50 per cent of the roof, the Planning Portal indicates a building control application is not usually required. Go past either figure and approval is needed, with possible insulation improvements. Checking your re-cover against those limits is part of our survey, and if the work is notifiable the paperwork is ours.
Does it matter if the tiles are holding up?
Sometimes torn felt is a nuisance and nothing more. A dry loft, tiles that are tight and unbroken, and no stains on the timber suggest the roof is coping. But the felt is your backup layer, and without it any later slipped tile or heavy storm lets water straight into the rafters and the insulation.
There is also a ventilation side. A hole in the felt can let wind pull air through the roof space, and in some roofs a modern breathable membrane is relied on to let moisture out, so a torn one stops doing that evenly. Our tile clips page and the notes on tile vents cover some of the fittings that work with the underlay.
Check for damp insulation or dark staining on rafters beneath the tear. Those marks tell you water has already found the gap.
What to do next
Photograph the damage with a torch and a phone, taking one picture of the whole bay and one close up. Do not poke or pull at the felt, and keep clear of the ceiling below if the area looks wet. Send us the pictures, or let us visit.
Our survey covers the underlay from inside and the tiles from outside, then a written quote follows with the photographs attached. If a small repair is enough, that is what we suggest. If the roof needs more, we say which parts and why. Dormer roofs and extensions have their own felt details, and our dormer roofs guide covers the awkward corners.
All pitched work from us carries a written 10-year workmanship guarantee, with the mess cleared before we leave. Call 01793 626096, or reach us by WhatsApp or the site enquiry form. The wider pitched roofing service page lists the other jobs we do.