Roof felt (or underlay) does a lot of work that never gets seen. It acts as a secondary barrier beneath the tiles, helping keep water away from the timber structure.
From experience, when roof felt starts to fail, the first signs often appear inside the loft rather than on the roof itself. Here are the most common signs that roof felt may need replacing.
Damp or Water Marks in the Loft
One of the first things people notice is damp patches on:
- Rafters
- Insulation
- Ceiling boards
If tiles look intact but moisture is still getting in, the felt underneath may be torn, sagging, or allowing water to track across it. This is especially common after heavy or prolonged rain.
Felt That’s Brittle or Crumbling
On older roofs, felt can dry out and become brittle.
If you touch it and it:
- Cracks
- Breaks apart
- Turns to dust
On older roofs, felt can dry out over time and lose its flexibility. Once it becomes brittle, it can crack or break apart with minimal movement, making it ineffective at keeping water out. Tears often develop around the nail holes or where the felt has weakened with age.
Tears or Holes Under the Tiles
Small tears can be caused by:
- Wind lifting tiles
- Foot traffic during past repairs
- Old nail holes opening up
Small tears or holes in the roof felt can allow water to get through even when the tiles above look fine. These openings often develop over time around nail holes, fixing points, or where the felt has become to brittle.
Leaks Without Obvious Tile Damage
One of the most common signs of failing roof felt is a leak when no tiles appear to be missing or broken. In these cases, the felt underneath is often the real issue rather than the tiles themselves.
Sagging Felt Between Rafters
Felt should sit fairly tight between rafters.
Roof felt should sit tight between the rafter’s. If it has started to sag, water can pool on the felt and eventually find its way inside.
Persistent Leaks With No Obvious Tile Damage
If leaks keep coming back and tiles have already been replaced, the problem is often underneath.
This is common on older roofs where tiles have been repaired multiple times but the felt has never been changed.
Can Roof Felt Be Repaired?
In some cases, yes.
Minor repairs might be possible if:
- The felt is generally in good condition
- The damage is small and accessible
- Tiles are being lifted anyway
However, patch repairs are usually a short-term fix.
When Replacement is Needed
Small issues with roof felt don’t always require s full replacement, but widespread damage, brittleness, or repeated leaks usually indicate it’s reached the end of its lifespan. Addressing the problem early can prevent damage to rafters, insulation, and ceilings.
When Full Replacement Is the Better Option
You should consider replacing the felt if:
- The roof is being stripped
- Battens are being replaced
- The felt is old, torn, or brittle throughout
Replacing felt during a re-roof is far cheaper than doing it later.
Final Thoughts
Roof felt plays a crucial role in protecting your home. If you’re seeing signs of damp in the loft or recurring leaks with no obvious tile damage, it’s worth having the felt checked before the problem worsens.
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