There are three main categories of single-ply roofing membranes: modified bitumen (which evolved from asphalt roofing and has other chemical components added); thermoset membranes (EPDM – essentially, synthetic rubber) and thermoplastic membranes, primarily PVCs (polyvinyl chloride) and TPOs (thermoplastic polyolefin).
Between thermoplastics, PVC has been in use since the 1960s, while TPO is a relative roofing newcomer, introduced in the 1990s. PVC and TPO membranes have a lot of similarities:
- Both PVC and TPO roof membranes are manufactured in many colors but typically installed in white, which gives them a cool, reflective surface, and makes them both great for energy savings.
- Both are recyclable, and some manufacturers have established post-use recycling programs that convert roofing materials into other products.
- Both are available in several thicknesses.
- For installation, both membrane types can be mechanically attached, adhered, or ballasted.
- Roof sections for both are hot-air welded – “seamed” – together on the rooftop. PVC membranes typically have a wider ambient temperature window for effective welding.
- Because they are both thermoplastic, the membrane material does not “cure” over time and remains weldable (in case patching is needed, for example) throughout the service life on the rooftop.
- Both provide good chemical and grease resistance (to varying degrees).
- Both can help a building achieve necessary fire ratings. PVC is inherently fire resistant; TPO is made fire resistant by adding fire retardant chemicals during manufacture.
The major advantage of TPOs compared with PVCs is price, as TPO membranes typically cost less per square foot of material. However, there are several factors that might make the overall cost of a TPO roof more expensive in the long run:
- TPO membranes tend to be stiffer than PVC membranes, making it more difficult for an installer to construct and install rooftop flashing components (for example) that retain their integrity and remain watertight over the roof’s life span. This might lead to increased maintenance costs down the road.
- Although TPO roofing products been around for 20 years, formulations have changed significantly and vary by manufacturer. How long has the formula for the TPO membrane you’re considering been in use? Does it have a proven track record? One manufacturer’s TPO membrane may not be ideally compatible with another’s, potentially making future patches and repairs problematic.
- In recent years, studies have shown that some TPO membranes have aged prematurely and deteriorated when installed in environments that get a lot of solar heat – regardless of whether it’s direct or reflected off nearby windows. This could require more frequent repair or an earlier replacement. Some manufacturers have addressed this issue by producing different TPO formulations and/or thicknesses – at a higher cost.
Both PVC and TPO systems enjoy large shares of the single-ply roofing market and are viable choices for most commercial roofing projects. Specific roof conditions may determine if one system is a better option than the other. Ultimately, the long-term quality of a roof installation is primarily dependent on the experience, skill and workmanship of the roofing contractor that’s chosen for the project.