TPO advantages include bitumen and polystyrene compatibility, very good low temperature flexibility, excellent puncture resistance, and increased welding rates. TPO is the fastest growing product type in the roofing industry.
TPO membranes are installed fully-adhered, mechanically-attached, or ballasted. Fully-adhered means that the roof is "glued" to the substrate using a special adhesive. Ballasted means the membrane is loose laid over the top of the roof, sealed at all penetrations and around the perimeter, and then a ballast is put on it to hold it in place. Ballast usually consists of smooth, round, river rock 2"-3" diameter. Mechanically-attached membranes are those that use some type of screw-type fastener to secure it. TPO sheets contain colorant, flame retardants, UV absorbers and other proprietary substances to achieve desired physical properties.
This system offers ease of installation, are lighter wieght, and usually a lower cost. Some of the concerns are punctures from heavy traffic, ponding water, delamination, shrinking, and chemical resistance.
Properly installed and mainatained TPO roofs should last between 15 and 20 years.