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 watershedding types of roof coverings installed on
slopes exceeding 3:12 (14 degrees).
There are five generic classifications of low slope roof membranes or systems. Click
on a roof system for more information.
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
With some roof membranes, a component may perform more than one function.
There are six generic classifications of steep slope roof coverings. Click on a
roof covering type for more information.
Steep-slope roof systems typically are composed of individual pieces or components
installed in shingle fashion. Steep-slope roof assemblies typically consist of three
- Roof deck a roof deck is the structural substrate and usually is a wood-based
material such as plywood or oriented strand board (OSB).
- Underlayment underlayment provides temporary protection until a roof covering
is installed and provides a secondary weatherproofing barrier. Sometimes underlayment
is referred to as "felt" or "paper."
- Roof covering the roof covering is the external watershedding material.