Built Up Roof Membrane
A built-up roof (Smooth Built-Up, Ballasted Built-Up, or Tar and Gravel) is a class of low-slope roof that consist of laying down several layers of tar and water resistant materials and then covered with gravel. Many old buildings with low slope or flat roofs are topped with built-up roofing made from layers of asphalt-coated roofing felt. The top layer is usually covered with rock or gravel, which serves as a ballast to hold the roofing material down and protect it from UV damage. Built-Up Roofs with gravel surfacing are also known as Tar and Gravel roofs. The typical life span of a built-up roof is 10 to 20 years depending on weather conditions.
Types of Built-Up Roofing
There are several types of built-up roofing alternatives.Built-up roofs are smooth Asphalt built up (Hot or Cold), and Ballasted Asphalt built up. The bitumen material commonly used in built-up roofing systems is asphalt, coal tar or cold-applied adhesive. The surfacing and materials used on built up roofing are so wide that it all depends on the project and costs of your project. Ballasted asphalt is being used more regularly than before, because it can provide an excellent finish surface and its material is a better fire retardant agent. Gravel or slag surfacing are probably the most popular. The next most popular surfacing are probably the granule-surfaced cap sheets, commonly called 90 pound because they used to weigh approximately that much per square. Now they weigh around 72 pounds per square. Then come the emulsions which can be spray, brush, or roller applied.Built-up roofs can be installed over just about any type of roof deck as long as the proper substrate is used. BUR’s can’t be mopped to a wood roof deck. In this case a rosin sheet and base sheet are needed first. With steel roof decks, the thickness of the deck should be a minimum of 22 gauge and some type of approved insulation should be mechanically-attached to the deck to provide a substrate.
How Long Do Built-Up Roofs Last?
The service life of a 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. This author has seen ten year old 4-ply roof that needed to be replaced and twenty year old 3-ply roofs that were still functioning.