Thermoplastic polyolefin (TPO) is a complex blend of polypropylene, polyethylene and other materials. It looks like plastic or rubber sheets and is widely used to cover flat roofs of commercial, institutional and industrial buildings. It is often covered with gravel "ballast" to prevent wind and sun damage. There are, however, some problems with TPO.
TPO is mostly polypropylene and polyethylene, but each manufacturer puts in different additives. Typical additives include some form of rubber to make it flexible and durable, some fire retardant, some ultraviolet (UV) retardant and a coloring agent. Unfortunately, only the coloring agent is obvious. This is where a lot of the problems come from--some manufacturers have left out the most expensive of the additives. This caused TPO to be taken off the market around 2000, but now it is making a comeback under the regulation of The National Roofing Contractors Association (NRCA) and other agencies.
TPO usually comes in sheets six feet wide and 0.05 inches thick, but it is also available in 12-foot sheets that are 0.08 inches thick. It can be attached with metal fasteners or glued to the roof. Sheets are attached to each other by overlapping them 1.5 inches and using hot air to fuse the sheets together. Hot air is also used to attach the sheets to pipes and other protrusions. These installations must be done by experts or under the supervision of experts. TPO is relatively resistant to tearing, but if it does tear (or is punctured), it can allow water underneath that will cause the TPO to degrade further. The ballast gravel that is added to hold the sheets in place and provide extra protection from the sun can contribute to tearing if disturbed by wind, maintenance men or birds. Structural damage and improper installation cause a lot of the TPO problems.
Age Related Problems
TPO is generally environmentally friendly and mold and algae resistant. The biggest problem with good quality TPO that was installed properly is sun damage. Over the years, the UV can weaken the TPO, and it will dry out and crack. This is especially a problem in the southern latitudes where there are more sunny days. A way to prevent the UV ageing problem is to buy white TPO. The white TPO usually carries the ENERGY STAR mark because it reflects 80 percent of UV radiation (ENERGY STAR requires 65 percent). This is the way to prevent a lot of TOP problems--look for the ENERGY STAR and NRCA stamps of approval that are displayed by responsible manufacturers.