Torn Or Sagging Roofing Felt In The Loft
- How urgent
- Caution
- Who fixes it
- A roofer
Key takeaways
- Torn roofing felt is a slow leak risk, not an emergency. Book a roofer within weeks if the timber is dry, and within days if it is wet or there is daylight through the roof.
- Do not patch torn felt from inside. Tape does not bond to brittle bitumen, and it does not give the water a way out to the gutter.
- One tear you can reach can sometimes be patched by lifting a few tiles. If the felt has failed across the roof, that slope normally needs stripping and re-covering with new underlay and battens.
- BS 5534 (the UK slating and tiling code) asks for a drape of a nominal 10 mm between rafters, and no more than about 15 mm. A deep swag that holds water or debris is not "normal sag".
- You normally need no building control application to repair or re-cover a pitched roof if less than half of the roof and less than a quarter of the whole building envelope is affected. Beyond that you need approval.
- If bats use your loft, the new underlay must be bat-safe: Type 1F bitumen felt, or a membrane that has passed the snagging test.
- Tradehand has no set price for this job yet, so get a local roofer's price through Instant Quote.
What does torn roofing felt in the loft actually mean?
Torn roofing felt means the underlay under your tiles has stopped doing its job. The underlay is the black sheet (older bitumen sarking felt) or lighter synthetic sheet (a modern breathable membrane) you see stretched over the rafters from inside the loft. Tiles are never fully watertight on their own: wind-driven rain and powdery snow get under them in storms. The underlay catches that water and runs it down to the eaves, where an eaves carrier tray drops it into the gutter.
Bitumen felt wears out with age. Heat cycling in the loft, UV light through gaps at the eaves or under a missing tile, and decades of flexing in the wind make it brittle. It then splits along the rafter lines and drops into swags. A torn sheet lets water fall straight onto the insulation, and a collapsed swag can hold standing water until it overflows onto the ceiling. A brown ring on an upstairs ceiling is often the first thing you notice (see water stain on the ceiling but no obvious leak).
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Is it old sarking felt or a breathable membrane?
Black, heavy, rough underlay that cracks when bent is old bitumen sarking felt, while a light synthetic sheet, often printed with the maker's name, is a breathable membrane. You can usually tell which roofing underlay you have by looking and touching from the loft, and it matters because the two age differently and suit different roofs.
| Bitumen sarking felt (often "Type 1F") | Breathable (vapour-permeable) membrane | |
|---|---|---|
| Look and feel | Black, heavy, rough, hessian-reinforced; cracks when bent once it is old | Light synthetic sheet that feels like plastic or fabric, often printed with the maker's name |
| Typical age | The most widely used underlay in the UK until the late 1990s (Historic England) | Most common on roofs laid or re-covered since then |
| How it fails | Goes brittle, splits along rafters, drops into swags | Tears where it was pierced or wind-flapped. Fitted too tight, it traps water behind the battens |
| Ventilation | Needs a ventilated loft (eaves and ridge vents) to control condensation, as BS 5250 sets out | Some products are certified for use with less ventilation, but only as their certificate allows |
| Bat roosts | Suitable: rough surface, low entanglement risk | Not suitable unless that product has passed the bat snagging test |
How urgent is torn roofing felt?
Torn roofing felt is not an emergency while the timber and insulation are dry, so book a roofer within weeks. If water is already getting in, or you can see daylight through the roof, book within days. Use this table after a look in the loft on a bright day with the loft light off.
| What you see in the loft | What it means | When to book a roofer |
|---|---|---|
| Brittle felt, small splits, dry timber and insulation | The felt is failing with age. No water is getting in yet | Within weeks. Plan the work |
| Swags holding dust, debris or water | The felt no longer drains to the eaves | Within one to two weeks, sooner if heavy rain is forecast |
| Tide marks or mould on rafters, damp or matted insulation | Water is already getting in | Within days |
| A line of daylight through the tiles and the felt | Both the tiles and the felt are open | Within days. Ask the roofer about temporary weatherproofing |
| Water near a light fitting, cable or junction box | Electrical risk as well as a roof one | Switch that circuit off at the consumer unit and call an electrician too |
Can torn roofing felt be repaired from inside the loft?
No, not properly. The roofing felt is laid over the rafters and under the battens and tiles, so you cannot lap a new piece under the old one from the loft side. Tape and adhesive patches do not bond to dusty, brittle bitumen. Even when they stick, they do not restore the drainage path down to the gutter. Water simply runs to the edge of the patch and drops off there.
What a homeowner can usefully do from the loft:
- Stand only on the joists. The felt and the insulation will not hold you, and a foot through the ceiling is the classic loft accident.
- Take photos of each tear and of any tide marks, with something in shot for scale. A roofer can price from them before visiting.
- Mark any ceiling stain below in pencil and date it, then check it again after the next heavy rain.
- Keep the gap at the eaves clear. Do not push insulation into the eaves to "fill" the draught, because that is the ventilation path that keeps the felt and timber dry.
- Move stored boxes away from wet patches so the insulation can dry out.
Repair or re-roof: what will a roofer actually do?
A roofer will either patch one reachable tear by lifting the tiles over it, or strip and re-cover the whole slope where the roofing felt has failed generally. To decide, the roofer looks at the felt from inside and the tiles from outside, because the condition of the tiles decides whether patching makes sense.
- Local patch. Where one tear can be reached, the roofer lifts the tiles and battens over it, laps a new piece of underlay under the sound felt above, then re-battens and re-fixes the tiles. This makes sense when the rest of the felt is still flexible.
- Re-cover the slope. Where the felt has failed generally, the roofer strips the tiles, lays new underlay with the correct drape, fixes new graded battens, and re-fixes the tiles or slates with the mechanical fixings BS 5534 sets for your area's wind exposure. Sound tiles are often reused.
- Eaves detail. The new underlay should be dressed onto an eaves carrier tray so it discharges into the gutter. If the old felt was cut short and dripped behind the gutter, that is why its bottom edge rotted first.
- Timber and ventilation. The roofer checks the rafters, battens and wall plates for rot, and makes sure the loft has a working ventilation path at the eaves and ridge so the new underlay is not fighting condensation from day one.
Before you agree a price, ask whether it includes scaffolding, new battens, any timber repairs, and disposal of the old felt.
Do I need Building Regulations approval to replace roofing felt?
Usually not for a small repair, but often yes for a re-roof. The Planning Portal says you will not normally need to apply to building control to repair or re-cover a pitched roof if less than half of the roof and less than a quarter of the whole building envelope is affected. You do need approval if you go past those limits, make structural changes, change to a covering that performs very differently in a fire, or use a new covering that is 15 per cent or more heavier than the old one.
Re-covering a large part of the roof can also count as renovating a "thermal element". Under the energy rules, if more than half of the roof is renovated, the whole roof is expected to meet current insulation standards where that is technically and economically feasible. Ask your roofer how building control will be handled before work starts. Some roofers belong to a competent person scheme that lets them self-certify.
What if bats live in my loft?
If bats use your loft, tell the roofer before any work on the roofing felt is booked. Bats and their roosts are legally protected in the UK, and work that affects a roost may need a licence. The National Bat Helpline gives free advice. The Bat Conservation Trust and Historic England both warn that most breathable membranes are made of long spun-bond fibres that bats' claws pull loose. Bats can then get tangled in them and die. In a bat roost, use hessian-reinforced Type 1F bitumen felt, or a membrane that has passed the industry snagging-propensity test, and keep the loft ventilated.
Is spray foam a fix for old roofing felt?
Spray foam is not a safe shortcut for failing roofing felt. Foam sprayed onto the underside of a pitched roof can trap moisture against the timber and hide rot. It can also make a mortgage valuation or survey harder to get signed off. The Property Care Association has published guidance on assessing sprayed foam in existing pitched roofs. Get independent advice before anyone sprays your roof, and treat a sales pitch at the door as a red flag.
How much does it cost to fix torn roofing felt?
The cost to fix torn roofing felt depends heavily on your roof, and Tradehand does not yet publish a fixed price for underlay repair or re-roofing. The quickest way to a real number is a local roofer's price through Instant Quote. What moves the price:
- Access: whether scaffolding is needed, and how high and steep the slope is
- Area: one patched tear, one slope, or the whole roof
- Tiles: whether they can be reused or need replacing
- Timber: whether battens, rafters or wall plates need repair
- Bats or building control, if either applies
Describe the job with your photos on Instant Quote. You get a price by text from local rates, then one local roofer takes the job. Your details stay with that business, and the quote is free for homeowners.
Questions people ask
Can torn felt be repaired from inside the loft?
Is sagging roofing felt normal?
Do I need underlay at all if the tiles are sound?
Why is my felt only torn at the bottom edge?
How long does roofing felt last?
Will home insurance pay for torn roofing felt?
Who fixes torn roofing felt?
A roofer fixes torn roofing felt, because the work is done from outside under the tiles. Tradehand lists roof leak repair and roofers across the UK, and our guide on how to spot a dodgy roofer covers the checks to make before anyone goes up a ladder. Related roof problems: slipped roof tiles, loose ridge tiles, crumbling verge mortar and a rotten or sagging soffit. New to pricing a job this way? Read how instant quotes from local tradespeople work.
Sources
- NFRC: Technical guidance
- BSI: BS 5534:2014+A2:2018, Slating and tiling for pitched roofs and vertical cladding (code of practice)
- Roof Tile Association: Installing underlay and tile battens
- Roof Tile Association: Use of vapour-permeable underlays in compliance with BS 5534
- Marley: Changes to BS 5534 since the 2014 revision (maximum 15 mm drape)
- BSI: BS 5250, Management of moisture in buildings
- Planning Portal: Building Regulations, work to an existing roof
- GOV.UK: Manual to the Building Regulations (renovation of thermal elements)
- Historic England: Works to roofs, walls and building services (building works and bats)
- Bat Conservation Trust: Roofing membranes
- Bat Conservation Trust: Non-bitumen coated roofing membranes
- Property Care Association: Sprayed foam insulation in existing pitched roofs
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