BUR is one of the oldest and most reliable ways of installing a new roof. It was first known as composition roofing and started in the 1840's. BURs come in two basic types - asphalt and coal tar - and three basic components – (1) the waterproofing component, (2) the reinforcing component, and (3) the surfacing component which is used to protect the other components from the elements.
The service life of a flat roof is dependent on many factors: geographical location & weather conditions, foot traffic, materials used, conditions under which the roof was installed, slope of roof, type of surfacing material, etc. Under ideal conditions, a 3-ply built-up roof should last at least fifteen years, a 4-ply should last at least 20 years, and a 5-ply should last at least 25 years. We have seen ten year old 4-ply roofs that needed to be replaced and twenty year old 3-ply roofs that were still functioning.