Low slope roofing includes water impermeable, or weatherproof, types of roof membranes installed on slopes less than or equal to 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 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. 

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