Asbestos Roofing Felt

Asbestos roofing felt is a bituminous membrane in which an asbestos fibre mat serves as the reinforcing core, saturated and coated with bitumen to produce a flexible, waterproof sheet. Manufactured from the 1920s through to the mid-1990s, it was one of the most widely used roofing materials for flat and low-pitch roofs in both residential and commercial construction.

The asbestos content in roofing felt typically ranges from 8 to 15 per cent by weight. Chrysotile was the dominant fibre type, chosen for its flexibility and tensile strength, which prevented the felt from tearing under thermal expansion and mechanical stress. The felt was produced in rolls and applied to flat roofs in single or multiple layers, bonded with hot bitumen adhesive. It was also used as underlayment beneath slate and tile roofs.

Flat roofs covered with asbestos roofing felt are found on an enormous number of buildings worldwide: residential garage roofs, house extensions, dormer cheeks, porch roofs, school buildings, commercial units, and industrial premises. In the UK alone, millions of flat roofs were covered with asbestos-containing felt during the post-war building boom. The material was favoured for its low cost, ease of application, and long service life.

When intact, asbestos roofing felt is non-friable and presents a relatively low risk because the fibres are encapsulated within the bitumen. The hazard increases significantly when the material is disturbed. Stripping old felt from a roof, particularly when it has become brittle and dry with age, can tear the asbestos fibre mat and release fibres into the air. Applying heat with a torch — a common technique for removing or re-layering roofing felt — is especially dangerous because it volatilises the bitumen and frees the asbestos fibres.

Before any flat roof refurbishment, re-covering, or demolition work on buildings constructed before the mid-1990s, the existing roofing felt should be tested for asbestos. If asbestos is confirmed, removal must be carried out by a licensed contractor using controlled stripping methods, wetting, and sealed waste containment. In some cases, overlaying new felt or a modern membrane system over the existing asbestos felt is permissible, provided the existing material is not disturbed.