Asbestos in the roofing felt is a more common finding than many property owners believe. Asbestos fibers were mixed with the bituminous felt, especially in the 1960s-1980s, because they strengthened the felt, improved tear strength and increased fire resistance. Old flat roofs, terraces and balconies almost always have layers of old felt, the composition of which cannot be determined visually. Roofing felt installed before 1994 must always be treated as possibly containing asbestos until laboratory analysis proves otherwise.
Why was asbestos used in roofing felt
Bitumen felt consists of a bitumen layer and a support structure, which can be made of felt fiber, glass fiber or asbestos fiber. Asbestos was chosen as a support material because it could withstand heat, improve dimensional stability of the felt and prevent tearing during installation. Asbestos felt was also long-lasting and durable against moisture, which made it a popular waterproofing material for demanding locations.
Typical sites where asbestos in roofing felt occurs
Asbestos in the roofing felt most often found in the following structures:
- Flat roofs in apartment buildings, townhouses and commercial buildings
- Terraces and roof terraces waterproofing
- Balconies waterproofing felt
- Garages and outbuildings low-slope roofs
- Industrial halls ceiling surfaces
- Underlays for gable roofs in older buildings
Often, several new layers have been installed on top of the old felt, so that the lowest asbestos-containing layer has remained hidden. However, this does not eliminate the risk, as all layers are removed when the roof is renewed.
Identification is not possible visually
The appearance of bituminous felt does not reveal whether it contains asbestos. Both asbestos-containing and asbestos-free felt can be black, gray or reddish-brown, and the surface grain can be granular or smooth. The only reliable way to ensure composition is to take a representative sample of each felt layer and submit it to an asbestos laboratory for analysis. The year of construction gives a strong indication, but not absolute certainty, because the old stock lots were still used in the early 1990s.
Dismantling releases fibers easily
The old bituminous felt becomes brittle over decades. When the felt is dismantled, torn or sanded, significant amounts of asbestos fibers are released into the air. Hot air blower, sawing and mechanical tearing all remove fibers. Fibers easily spread from the roof to the surrounding yards, ventilation ducts and spaces below. Therefore, demolition of asbestos-containing felt must always be done by an authorized asbestos removal company and with appropriate protective measures.
Roof renovation requires an asbestos survey
Finnish legislation requires an asbestos survey before all demolition and repair work on structures completed before 1994. Roof repair is part of these jobs whenever old felt is removed or penetrations are made. In the survey, the roof felt layers are sampled and analyzed. Based on the report, the contractor can price and plan the work correctly, and the property owner avoids surprises.
If a flat roof, terrace or balcony requires renewal in a property built in the 1960s-1980s, order an asbestos survey before selecting a contractor. In this way, the renovation proceeds safely and legally without delays.