Torn Or Sagging Roofing Felt In The Loft

What's happening?

The layer you can see from inside a loft is the roof underlay — older bitumen sarking felt or a modern breathable membrane. It is the secondary barrier: it catches wind-driven rain and snow that gets past the tiles and drains it out at the eaves. Bitumen felt has a finite life. UV through gaps, decades of heat cycling and constant flexing make it brittle, and it eventually tears along the rafter lines and drops in swags between them. Once torn, water that gets past a tile drips onto the loft floor and the insulation instead of running out. A collapsed swag also holds standing water, which is how a small tear becomes a wet ceiling.

What usually causes it?

• Age-related embrittlement of bitumen sarking felt, common on roofs laid several decades ago
• UV exposure through gaps at the eaves, verge or a missing tile, which degrades felt fastest
• Felt laid without support so it sagged from the start and now holds water and debris
• Rodent, bird or squirrel damage where access into the loft has been available
• Physical tearing during earlier work — aerials, cabling, insulation top-ups or solar fixings pushed through it
• Condensation soaking the felt from the loft side where there is no ventilation path, accelerating decay
• Felt dressed short at the eaves so it discharges behind the gutter instead of into it, keeping the lower edge permanently wet

When should you call a roofer?

Call a roofer within weeks for torn felt with dry timber, and within days if timber is damp, insulation is wet, or you can see daylight through the roof. This is normally the point at which a roofer will talk about re-covering rather than repairing, because underlay sits under the tiles and cannot be replaced from inside — reaching it means stripping the covering. Getting that assessment early lets you plan the work rather than react to a collapsed ceiling.

What will the roofer actually do?

• Inspect from inside and outside to judge whether the tiles have life left, since that decides repair versus re-cover
• Check rafters, battens and wall plates for rot and for the tide marks that show how long water has been getting in
• Patch locally where a discrete tear can be reached by lifting a small area of tiles
• Strip the covering and lay new breathable membrane over the affected slope where the felt has failed generally
• Renew battens as required and re-fix the tiles or slates with the mechanical fixings BS 5534 specifies for your exposure
• Dress the new underlay correctly at the eaves, over an eaves carrier tray, so it discharges into the gutter rather than behind it, and confirm the loft has a working ventilation path at eaves and ridge so the new membrane is not fighting condensation from day one