What is a Thermoplastic Single Ply Roof?

If you have done any research about commercial flat roofing over the last few years, you have doubtless come across the term "Single Ply Roofing".  So what the heck is a "Single Ply Roof" anyway? You can trouble yourself no more, because today we are going to discuss Thermoplastic Single Ply Roofing Systems! When you are done reading this article you'll have a well rounded understanding of the basics. 

Thermoplastic single ply membranes represent the fastest growing segment of the U.S. new construction roofing market over the past five years.They come in two basic varieties, PVC and TPO (there are others, but for the purpose of this article we are going to stick with the most popular). PVC is commonly referred to as "Vinyl" and TPO is commonly referred to as "Plastic".

The PVC (polyvinyl-chloride) product is a reinforced membrane with hot-air welded seams. This material has excellent durability and dimensional stability and is the category leader for dependability and longevity. Since the 1960s’ PVC has an unblemished history of commercial roofing performance.


The TPO (thermoplastic-polyolefin) is relatively new to the single ply category; wide spread distribution and application started in the mid 1990’s. TPO combines the hot-air welding benefit of PVC with the promise of greater flexibility and weatherability benefits. While TPO has good testing results in the laboratory, results from the field are troubling to say the least. 

Both PVC and TPO are aesthetically pleasing, lightweight, highly reflective, and chemical resistant. They also offer nominal fire resistance.

SINGLE-PLY BENEFITS
Resistant to chemicals
Reflective, California Title-24 Compliant
Green Building Counsel approved for LEED points
Energy Star rated to decrease HVAC cooling costs
Safe to install


SINGLE-PLY DRAWBACKS
One layer -Single ply roofs have no redundancy of waterproofing. The thin top layer is the entire roof. One puncture, tear, or open seam and moisture can easily enter the facility.  If the system is mechanically fastened water can migrate below the system, making leak detection and correction very difficult. Mold can easily grow when moisture is trapped between one of these ultra thin roofs.
Seams - miles and miles of seams that all need to be heat welded. Miss one sean and you can have a severe leaking and other related water intrusion issues.
Safety Concerns - these roofs are very slippery. Early morning dew and a slippery surface can be a recipe for disaster. If you choose one of these systems make sure you have a full safety rail system and walk pads installed.
Cost - These systems can be very expensive to install. Compare all of your options before buying. 
Puncture issues - Because these membranes are very thin, with average thickness of only 50 mils thick - they can be easily punctured. One sharp edged toolbox can cause thousands in damages.

Additional drawbacks of TPO membranes - TPO membranes have an extremely short track record. TPO Manufacturers have changed their formulations year after year due to problems. The product that ends up on your roof could have less than a few months of 'real world' application.  There is also cause for concern when TPO is applied in areas of High Solar Loading. The Midwest Roofing Contractors Association has gone so far as to issued a "bulletin" warning that the use of TPO membranes in areas of High Solar Loading can lead to premature membrane failure. The problem has become so prevalent that there are a number of Class Action lawsuits pending.

If you choose to install one of these single ply systems, my personal preference is the time proven PVC system. You will pay a bit more up front, but you will have a product that is field tested and reliable.

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