The built-up roof is generally a flat roof, or a low pitched roof, which is made of a number of levels. The gravel and tar built-up roof is the one most commonly known. A gravel and tar built-up roof is exactly that – layers of gravel and asphalt laminated felt on top of a flat roof.
Problems with Various Styles of the Built-up Roof
- Asphalt degradation of gravel and tar roofs is a common problem and concern.
- Ultra-violet radiation on hot rooftops can oxidize the surface of the asphalt and produce a chalky residue.
The plasticizers inherent to the asphalt gradually leech out, causing the roof to become brittle and prone to cracking. Alligatoring as well as blistering occurs in this type of asphalt built-up roof, which allows water leaks. This is a very common problem in city buildings with asphalt built-up roofs.
Installation of asphalt built up roofs contributes also to air pollution, and the roof gives off toxic greenhouse gases. Flat membrane roofs are preferred in current construction, though a great number of asphalt built-up roofs still exist.