There are many choices to make when you are looking to replace your commercial roof. Due to the number and complexity of options facilities managers often leave this decision to their roofing contractor. Other times, architects will decide. But arming yourself with this knowledge will give you the opportunity to ask pertinent questions.

Flat roof systems are long term capital investments that will protect your building for decades to come. Making sure you’re getting the most out of your hard-earned dollars is just a sensible thing to do.

Bear in mind that the best product in the world will still fail if improperly installed. Success is almost always a collaboration of (1) a quality product installed by a (2) quality commercial roofing contractor. If you remove one part from that equation it is generally unreasonable to expect that you will get the best results. Remove both from the equation? Well, I’m sure you can do the math. The following are some points for comparison in commercial roofing products:

Breaking Strength

A majority of TPO roofing systems that are installed are mechanically fastened to the roof deck. Breaking strength is a critical measurement of a sheet’s strength if the membrane is ever subjected to extreme forces, such as excessive wind, against the fasteners that hold it in place. The ASTM breaking strength test consists of a machine pulling the membrane in opposite directions and recording the amount of force necessary to create membrane failure.

Tearing Strength

Tearing strength is very similar to breaking strength and its importance is just as critical. Tearing strength is a measurement of how much force is required to rip the membrane from the edge, as opposed to breaking strength which involves pulling opposite ends of the sheet in different directions. Tearing strength results are also measured by adding the results of the force required to tear the sheet both across and down the sheet. The main benefit to a high tearing strength value is experienced when a small cut in the membrane occurs. By having high tearing strength a small cut is less likely to become a large tear, which can lead to excessive damage.


In a recent survey contractors listed ease of installation as the physical characteristic that they use most often to determine which membrane they prefer to install. Ease of installation is defined in part by flexibility. The more flexible the membrane, the easier it is to complete details and install the membrane. Furthermore, the more flexible the membrane, the easier it will expand and contract with your building as the seasons change and your building settles over time.

Puncture Resistance

On a properly installed TPO roofing system a common way for leaks to occur is through punctures in the membrane. By ensuring that the membrane installed has high puncture resistance and the manufacturer has the ability to provide an accidental puncture warranty, leaks due to punctures in the membrane can be mitigated and handled in a timely manner.

Seam Strength

A chain is only as strong as its weakest link. It is extremely important that the seam of a TPO roofing system does not become that weak link. If welded properly the seam areas should be stronger than the sheet itself. A wide range of weldability will help ensure a solid seam at various temperatures and conditions without adjusting speeds and temperatures of the welder.

Thickness Over Scrim

While it’s important to have a thick sheet, which is measured in the “Thickness Overall” test, “Thickness Over Scrim” measures the top-ply of the TPO membrane. TPO consists of a top-ply, scrim in the middle and a bottom ply. The top-ply is the front line of defense against the elements and the usable life of the membrane is compromised when the scrim is exposed. Thickness over scrim is a critical measurement when evaluating the potential longevity of a TPO roofing system.

Weathering package

According to Carlisle Syntec, a TPO membrane is enhanced with a weathering package that helps protect the integrity of the membrane and prolong its service life. The thicker the membrane, the more weathering package per unit of surface and the longer the membrane will retain its smooth, glossy finish.


A wide window of weldability will help ensure a solid seam is created at various ambient temperatures and weather conditions without adjusting speeds and temperatures of the welder. In addition to more consistent seaming, a wide window of weldability provides labor savings and an easier to install roofing system.


There are many types of warranties on your roofing: from the contractor roof warranty to manufacturer roof warranty. Then on the manufacturer warranty there is the difference between a material-only vs labor-only vs total system warranty.

*Our thanks to Carlisle Syntec for providing a portion of the information in this post.

Leave a Reply