Flat roofs are common in areas with little rainfall or snow and on industrial buildings with wide roof spans, but are also found on homes with large areas on roofs that have a small or no pitch. The following products are typically used on flat roofs:
- Tar and gravel roof: This type of roofing is used primarily on flat roofs up to a 3-in-12 pitch. Even flat roofs are sloped somewhat to prevent water from ponding. Tar and gravel roofs are constructed from alternating layers of heavy roofing felt and hot asphalt or tar and finished with a protective mineral coat, such as gravel or mica. The roofs are rated by how many layers are installed, usually from three to five. Read more about Built-up Roofing.
- Modified Bitumen Roofing: This type of roofing combines many of the features in the standard tar and gravel roof with the addition of layers of polyester or fiberglass impregnated with bitumen, a derivative of tar or asphalt. The roofing is put down in multiple plies, or layers, and gains significant strength and resistance to weathering by adding the polyester membranes. Other bitumen modifier agents that enhance asphalt's qualities include atactic polypropylene (APP) and styrene butadiene styrene (SBS). Read more about Bitumen Roofing.
- EPDM rubber roofing (EPDM): stands for ethylene propylene diene monomer and is a synthetic rubber membrane which can stretch up to 300% elongation, allowing for expansion and contraction in the building where it is installed. It is virtually unaffected by Ozone and UV radiation, therefore far longer lasting than bitumised products. It does not crack tear or split and is manufactured in various sizes of sheet greatly reducing the number of joints required in a large roof. Read more about Rubber Roofing.