Classifications of low slope roof membranes or systems:
- Built-up roof (BUR) membranes
- Metal panel roof systems for low-slope applications
- Polymer-modified bitumen sheet membranes
Typically, low-slope roof assemblies are composed of three interrelated components: the roof membrane, roof insulation, and the roof deck. The roof system is defined as the roof membrane (including surfacing) and the roof insulation. The roof assembly is defined as the roof deck, along with the roof membrane and roof insulation. Low-slope roofs are often referred to as flat roofs. Roof assemblies with a pitch (slope) of less than 3:12 are considered low-slope roofs.
Most low-slope roof membranes have three principal components:
- Weatherproofing layer or layers
The weatherproofing component is the most important element because it keeps water from entering a roof assembly.
Reinforcement adds strength, puncture resistance and dimensional stability to a membrane
Surfacing is the component that protects the weatherproofing and reinforcement from sunlight and weather. Some surfacings provide other benefits such as increased fire resistance, improved traffic and hail resistance, and increased solar reflectivity.
With some roof membranes, a component may perform more than one function.