TPO and PVC: Thoughts & Concerns
Over the last decade, TPO (thermoplastic polyolefin) roofing membranes have become the most popular choice for flat and low-slope roofs. They are even used for roof recovers and attached over old roofs. PVC (polyvinyl chloride) is also a thermoplastic membrane that was the dominate single-ply until the recent rise of TPO. Thermoplastics are strong materials and typically produced in reflective white colors. They comes in rolls and are mechanically attached with fasteners into the deck, fully adhered using glue and adhesives, or heat-welded to induction plates that fasten the insulation or cover board down. The seams are overlapped and welded together with hot air. Typically, TPO and PVC welds hold strong over time. It is supplied in 60 mil (1.5 mm), 72 mil (1.8 mm) or 80 mil (2 mm) thick sheets, though a portion of the thickness is taken up by the reinforcement scrim. There is thermoplastic polymer material, which is the actual waterproofing, above and below this scrim. The thickness above the scrim depends upon the manufacturer and the quality of their TPO or PVC.
Some manufacturers, such as Duro-Last and Fibertite, are even selling 40 mil thick sheets. In this instance, they state in their literature there is only 17 mils of PVC polymer above the scrim. This means you only have 17 mils of waterproofing to withstand UV, ponding water, and the elements before the scrim is exposed.
TPO became popular for many reasons, mostly economical, as it is the cheapest rolled roofing membrane in the market. It is lightweight, safe to install, durable, and energy efficient. No open flames, and no hot kettles. You could lay insulation board or hard board over an old roof, or use fleeceback membrane, and then roll out a TPO or PVC for a completely new, warranted system. However, most of the time this requires thousands upon thousands of fasteners to go through the old roof and the old deck in order to hold it down. Every seam must be welded perfectly, every flashing done correctly, and everything sealed with caulk in order to prevent the creation of a water bed.
The photos below I took in Las Vegas recently on a 14-year old TPO roof. You can see where the UV rays had been reflecting off of the parapet wall onto the field. What happens is a magnifying effect. The UV that bounces off the wall is more intense and deteriorates the TPO membrane faster. Remember, there is only 15-23 mils on average of material before the scrim is exposed. The scrim can then absorb water and moisture can actual wick through the scrim. This not only causes leaks but accelerates degradation of the rest of the sheet.
TPO became popular due to the discovery that PVC roof membranes had, under ponding water, their plasticizers “migrate”. This means the plasticizers that comprise the PVC polymer structure actually move out of their originally intended position. The result is brittleness and loss of stability. However, this greatly depends on the manufacturer and the type of plasticizers they use and how they are integrated during manufacturing. Plasticizer loss has been studied and analyzed extensively by prominent PVC manufacturers, such as our partner, Protan. I also want to note aged TPO is difficult to weld new TPO to. The welds typically don’t hold, so it must be repaired with tapes or peel-and-stick TPO. Protan PVC, on the other hand, can still be heat welded even after 30 years of service.
The other issue that led to the rise of TPO was the ease of welding during installation Plus, they are much cheaper! It would make sense that TPO is the way to go, right? Unfortunately, you get what you pay for. TPO membranes are struggling to last 10 years in many instances as the TPO polymer materials are not as strong, durable, and long-lasting as PVC. Many of you have likely experienced this firsthand. TPO manufacturers continue to modify and play with their formulations, whereas the highest quality PVC formulations haven’t changed in decades and have proven, documented lifespans.
PVC membranes do have their place in the market, despite some issues and maintenance requirements to ensure watertight performance. They are the most chemically-resistant rolled roofing membrane, lightweight, safe to install, and have predictable life expectancies. Triton believes in full roof replacement situations, or for new construction, PVC single-ply membranes are the best choice. A major downside to both TPO and PVC membranes is the smooth, slippery surface. When wet with dew or rain, this leads to a high number injuries from slips and falls. Triton has changed that by providing the only high-friction thermoplastic membrane in the industry through our partnership with Protan.
All of this proves why liquid-applied membranes are continuing to rise and gain a much larger footprint in the roofing industry. For restoring an existing roof membrane, a liquid membrane like ours makes the most sense. Unless, of course, the existing insulation is saturated or the old roof is completely shot and a tear-off is the only option. As these TPO roofs show signs of premature failure, a lot of money is being saved by being pro-active and restoring them with our TritoFlex 2K thermoset set rubber system.
If you’re interested in learning more about our stronger, safer, and sustainable approaches to roofing, reach out to me anytime.