Felt Roofing Problems: What Goes Wrong and How to Fix It

Millions of UK homes have traditional mineral felt flat roofs. While modern systems have largely superseded felt, it remains in use and presents specific maintenance and repair challenges. Here's what to look out for.

Blistering

Blistering — bubbles in the felt surface — is the most common felt roofing problem. It's caused by moisture or air trapped beneath the felt during installation, which expands when heated by the sun. Small blisters can be left if they're not cracking, but larger blisters, especially those that have cracked open, must be repaired to prevent water ingress.

Splitting and Cracking

As felt ages, it becomes brittle and develops splits and cracks, particularly at laps and around upstands where it was bent during installation. These allow water in and worsen rapidly once established.

Lifting at Edges and Flashings

The edge of the felt and at any upstand flashings are common failure points. The adhesive or sealant can degrade, allowing the felt to lift and water to track behind it.

Repair vs Replace

Individual repairs to felt can buy time, but if the felt is more than 12–15 years old and showing multiple problems, it's usually more economical to replace the whole roof rather than patch repeatedly. A patchwork felt roof is a symptom of ongoing failure, not a solution.

Best Replacement Option

When replacing an old felt roof, we strongly recommend upgrading to GRP fibreglass or EPDM. The cost difference over the roof's lifetime is significant in favour of the modern system.