Bituminous Roofing 101

Bituminous Roofing in Northern Virginia

Bituminous roofing materials have stood the test of time and carry an established track record to low-slope roofing. Bituminous roofing systems are well-known for their toughness, dependability, and excellent waterproofing.

Built-up roofing (BUR) and multi-ply, polymer-modified bitumen are the two primary types of bituminous roof systems. SBS and APP membranes are the two most popular polymer-modified bitumen membranes on the market.

Built-Up Roofing (BUR)

In the United States, BUR systems have been in operation for over a century. BUR structures are made up of layers of oxidized bitumen and bitumen-coated membranes, which are often referred to as felts or ply sheets. A dimensionally stable, high tensile strength fiber glass mat is commonly used to reinforce ply sheets. The redundant, multi-ply approach ensures the system provides dependable waterproofing for many years. BUR systems are surfaced with an aggregate or roof coating to increase the weathering capability of the system, and the redundant, multi-ply approach ensures the system provides dependable waterproofing for many years.

Modified Bitumen (Modbit) Systems

The most dependable waterproofing benefits of a BUR system are shared by Modbit systems, which consist of base plies and a cap sheet. Modbit systems are extremely adaptable. Cool roof granules and coatings can be used to reflect UV rays, raising the long-term performance of the roof and reducing energy costs for the building. Cap sheets in modbit systems are surfaced with a mineral granule to improve the weatherability of the structure, and cool roof granules and coatings can be used to reflect UV rays, increasing the long-term performance of the roof and lowering energy costs for the building.

SBS Membranes

Bitumen has been modified with elastic Styrene-Butadiene-Styrene (SBS) polymers to form a “rubberized” asphalt coating for SBS membranes. The coating is applied to a fiber glass reinforcement carrier for high tensile strength and dimensional stability, polyester for superior elongation and tear strength, or a combination of the two. SBS membranes are extremely flexible, particularly in cold temperatures. Self-adhering SBS membranes are available, but most are built with mopping asphalt or cold adhesive.

APP Membranes

APP membranes are made of bitumen that has been modified with plastic Atactic Polypropylene (APP) polymers to provide a coating with the widest temperature range, as well as increased durability and toughness. The coating is typically applied to a polyester carrier mat, but fiber glass products are also available. Due to the plasticized bitumen’s meltability, APP membranes are often torch-applied.

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