What is TPO Roofing?

TPO (thermoplastic polyolefin) is one of the best solutions for commercial roofs for many reasons including cost, energy efficiency and longevity. TPO is a single-ply membrane material used on flat roof systems. It is impact resistant and very flexible which allows it to adapt to the expanding and contracting of any building upon which it is installed. TPO is available in several thicknesses from .40-mil (.04”) to .90-mil (.09”), the most common being 45-mil, 60-mil and 80-mil.

Does TPO Roof Thickness Matter?

Yes. Thicker TPO performs better for longer periods of time but requires a greater investment. When TPO is applied to a roof for the first time, a thicker membrane is preferred and performs best over twenty to thirty years. A thinner membrane is best used when applied to a pre-existing membrane.

To fully appreciate the importance of thickness in the context of a new TPO roof, you must first understand of what a TPO membrane consists. There are three layers:

1. the bottom: polymer layer
2. the middle: polyester reinforced fabric center layer (commonly referred to as “the scrim”)
3. the top: thermoplastic polyolefin (the waterproof material)

With ideal weather conditions, TPO roofs generally wear about 2 mils of thickness per year.

Labor is another expense to consider. As you increase the thickness of the membrane, it becomes stiffer and more difficult to install which costs more. Consider only experienced TPO installation crews to ensure the greatest chance of success and performance.

How To Install a TPO Roof

First determine what material is currently installed on the roof. If it is anything other than a membrane material such as a gravel roof, you must first remove the old roofing material down to the roof deck. Ensure that the substrate of the old roof is completely clean, and all debris and dust are removed. Next, cut and place insulation boards around the entire roof surface. Secure the insulation boards to the roof substrate with screws.

Mechanically Attached vs. Adhered TPO Roofs

Mechanically attached TPO roofs include plates which are aligned with holes spaced 6-8” from center within the membrane material at the seams. Screws are then placed into the plates and a drill is used to secure them to the insulation boards. Different screw fastening patterns can also be used depending on the specifications of the building the new roof is to be installed on.

Adhered TPO roofs differ from mechanically attached TPO roofs in that they use a bonding adhesive to secure the membrane to the insulation boards instead of plates and screws. Adhesive is applied to both the insulation board and the underside of each TPO sheet. Once the adhesive has had time to become “tacky”, you can adhere the membrane. Finally, use a pressure roller to ensure a proper seal.

Installing a New TPO Roof over an Old Membrane Roof

For roofs with a pre-existing membrane roof, the new TPO can be installed over the existing membrane as an additional layer. It is in these cases, thinner TPO may be applied.

It’s best to check your city and/or county regulations prior to layering a new TPO roof over an older membrane roof. Some cities and counties only allow membrane roofs to be re-layered up to two times.

Furthermore, it’s best not to layer a membrane roof more than twice as any underlying issues with the older membrane roofs may become so hidden and expansive that removing all the material including the new roof may be the only method to repair leaks and other roofing issues.