A flat roof is a roof which is almost level in contrast to the many types of sloped roofs. The slope of a roof is properly known as its pitch and flat roofs have up to approximately 10°. EPDM: is a synthetic rubber most commonly used in single-ply roofing because it is readily available and simple to apply. Seaming and detailing has evolved over the years and is fast, simple and reliable with many membranes including factory applied tape, resulting in a faster installation. The addition of these tapes has reduced labor by as much as 75%. TPO: Thermoplastic Polyolefin single-ply roofing. This roofing material can be fully adhered, mechanically fastened, or ballasted. TPO seam strengths are reported to be three to four times higher than EPDM roofing systems. This is a popular choice for "Green" building as there are no plasticizers added and TPO does not degrade under UV radiation. It is available in white, grey, and black. When this technique is properly applied, in appropriate places, its warranted life-span has reached 30 years and its expected lifespan has reached 50 years.