Explanation of Low-Slope Roof Systems

All roofs have a slope to ensure proper drainage. When it comes to low-slope roofs, also known as "flat" roofs, the slope is very slight, usually less than a 3:12 ratio. This ratio represents the rise of the roof (vertical) over the distance (horizontal) between its lowest and highest edges. For example, a 3:12 slope indicates a rise of 3 inches over a 12-inch distance.
In the Fresno area, there are several common types of low-slope roof systems. Let's delve deeper into two examples: Built-up Roof (BUR) Membrane Systems and Polymer-Modified Bitumen Sheet Membrane Systems.
1. Built-up Roof (BUR) Membrane Systems:
Built-up Roof (BUR) Membrane Systems consist of multiple layers that work together to provide a durable and weather-resistant flat roof. The layers typically include insulation board, perlite (a lightweight volcanic glass material), inter-ply sheets, asphalt, and pea gravel ballast. These layers are repeated in various combinations to enhance the strength and longevity of the roof.
This system is installed by first applying the insulation board to the roof surface, providing both thermal insulation and a stable base. Next, a layer of perlite is added to increase the roof's fire resistance and improve its insulation properties. On top of these layers, an inter-ply sheet is installed, typically made of fiberglass or polyester, to serve as a reinforcement.
The asphalt layer is then applied, usually with a bituminous material, acting as a waterproof barrier. Finally, pea gravel ballast is spread over the surface to protect the roof from weathering and provide additional fire resistance.
2. Polymer-Modified Bitumen Sheet Membrane Systems:
Polymer-Modified Bitumen Sheet Membrane Systems offer an alternative approach to low-slope roofing. These systems consist of reinforced bitumen membrane fabrics that are applied using various methods, including hot asphalt mopping, heat welding, or torch application.
The bitumen membranes used in this system are reinforced with materials like fiberglass or polyester. These reinforcements enhance the strength and flexibility of the membrane, allowing it to withstand the stresses and movements typically experienced by flat roofs.
The installation process involves heating the bitumen membrane, which softens it and enables it to adhere securely to the roof's substrate. This ensures a watertight seal and protects the underlying structure from moisture infiltration.
Polymer