Single Ply – EPDM
EPDM is similar to TPO in the fact that it is a single ply membrane, however EPDM is a rubber compound instead of plastic, like TPO. EPDM has a strong reputation for durability. With properly taped seams and detailed flashings, an EPDM roof can easily last 30 years. However, unlike TPO, the seams are treated with adhesive making them vulnerable over the long term and will eventually require maintenance.
EPDM is commonly installed mechanically fastened, fully adhered, or ballasted. Ballasted EPDM roofs are very economical on large projects, when the structure can support the weight of the rock ballast.
EPDM is available both reinforced with polyester scrim and non-reinforced in thick nesses ranging from 45 to 90 mills. 90 mill EPDM is the only EPDM membrane eligible for a 30 year system rating.
Definitions of Single Ply installation methods:
Fully adhered - a roofing system or a component of that system that is glued in place or otherwise secured with adhesives. Fully Adhered roofs carry system ratings of 15-20 years (30 years on EPDM with proper construction of the roofing assembly).
Mechanically fastened - a roofing system or a component of that system that is secured in place using fasteners of some kind. Often these fasteners are button head nails or screws with plates. Regular shingle style roofing nails are not acceptable. Mechanically fastened roofs carry system ratings of 10-15 years.
Ballasted - a roofing system that is not fastened nor glued in place. Instead the roof is weighted in place by the application of washed river rock, manufactured concrete pavers or other media of substantial weight. Ballasted single ply roofs carry system ratings of 10 years.
Mill Thickness can be translated into inches for better understanding. Since 1 mil = 0.001" (or 1/1000 of an inch; hence it being called a "mil"), 45 mils = .045". In fractions a 45 mill membrane would equal approximately 1/22".