Built-up roofs are made of various layers of continuous, waterproofed material. They are composed of several layers of bitumen surfaces and topped with an aggregate layer or coating. The term ply sheet refers to a single layer of roofing. While the surfacing and materials used in built-up roofing vary, one example of built-up roofing is a base sheet attached to the roofing substrate, a ply of roofing felt, top that with a layer of bitumen, and lay another sheet of felt. Cap that layer with gravel or cap sheets. Hold these layers down with a final layer of asphalt.
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Usually, the bitumen used in a BUR system is asphalt, coal tar, or cold-applied adhesives. Although the roof membrane can be left bare, it is normally covered with waterproofing material and gravel to protect the roof from ultra-violet degradation and stabilize temperature changes. The gravel also weighs down the roof and protects it from wind damage. The multi-layer protection in a built-up roof creates a strong, durable roof membrane. More recently, built-up roofs include an insulation layer for better temperature control. The ply sheets are often reinforced with fiberglass or organic mats, adding to the stability of the roof.
Built-up roofs, commonly referred to as tar and gravel roofs, can be applied by a variety of methods. For hot applications, the asphalt or coal is heated in a kettle or tanker and then applied by mop or a mechanical spreader. Cold built-up roofing can be sprayed on or applied with a squeegee. Because it does not need to be heated, cold applications do not create toxic fumes and are better for the environment.
Built-up roofing has many pros. These roofs are low maintenance and endure severe weather. They have excellent waterproofing qualities and provide ultra-violet protection. There are also a few cons to consider. Installation is slower and costs more than some other types of commercial roofing. Care needs to be taken with the hazardous fumes and vapors when installing it. The roof can be susceptible to wind damage if not installed correctly.
Built-up roofing has been used in the United States for over 100 years and is a favorite material used on low-slope buildings.
One of the best ways to repair a BUR roof is with Conklin’s Spray Poly Foam system. It adds a layer of foam on top of the roof and creates a seamless cover over the whole roof. The highly reflective Conklin coating is sprayed on top to finish the roof off. Because it is all sprayed on, it makes it very easy to go over a rough surface and still bond extremely well.