Roof system types
Roof systems and materials generally are divided into generic classifications: low slope and steep slope. Low slope roofing includes water impermeable, or weatherproof, types of roof membranes installed on slopes less than or equal to 3:12 (14 degrees). Steep slope roofing includes water shedding types of roof coverings installed on slopes exceeding 3:12 (14 degrees).
There are five generic 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
- Single-ply membranes
- Thermoplastic membranes (e.g., PVC, TPO)
- Thermoset membranes (e.g., EPDM)
- Spray polyurethane foam-based (SPF) roof systems
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 — reinforcement adds strength, puncture resistance and dimensional stability to a membrane.
- Surfacing — surfacing is the component that protects the weatherproofing and reinforcement from sunlight and weather. Some surfacing 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.