What is TPO Roofing? A Great TPO Roof Guide for Non-Roofers

By Jack Gray, Roof Online Editor • Updated October 3, 2022

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Table of Contents

Recently installed fully-adhered TPO roofing.
A fully-adhered TPO roof

Pictures of TPO Roofing

Introduction

TPO roofing is becoming more and more familiar to building owners and property managers – it’s that bright white roofing membrane constantly being recommended by roofing contractors.

The first time a “TPO-type” roofing product was used in the U.S. was around 1987, but in the last 15 years, interest in TPO roofing has skyrocketed. We’ve noticed more and more clients asking about TPO when their old roofs are starting to fail and it’s time to discuss a roof replacement.

TPO is now the most popular single-ply roof membrane in the United States when it comes to new low-slope roof installations.

Unfortunately, it’s hard for most people to find good information on TPO roofing. There is no reputable TPO Roofing Association the way there’s an EPDM Roofing Association.

Because of TPO’s limited history as a roofing material in the US, there isn’t a large body of TPO roofing research, technical papers, practical guides, or other reliable reference resources like there is for more established materials such as asphalt, EPDM, or PVC.

Most of the TPO roofing information that you find on the internet was written by roofing contractors who are trying to sell you a TPO roof.

We’re professional roof consultants – professional roof experts, you might say. Our clients include homeowners associations, corporate real estate asset managers, property managers, and facility directors.

As a part of our job, we research and write specifications for new TPO roofs. We inspect TPO roofs and provide quality assurance during TPO roof installations. We’ve overseen maintenance and leak repair programs for quite a few TPO roofs.

We have to make sure we’re up-to-date on the latest developments in TPO roofing.

We know TPO roofing pretty well, and we thought we would share some helpful information about TPO roofs here on our website.

What is TPO Roofing?

TPO roofing is a type of single-ply roofing in which sheets of TPO membrane are used as the primary waterproofing material. TPO, which stands for thermoplastic polyolefin, is heat-weldable (that’s the thermoplastic part) and extremely UV-resistant.

TPO Roof Membrane

The TPO membrane is delivered from the factory in large rolls. The sheets are typically 10 feet wide and 100 feet long, although there are many other sizes available.

The standard thicknesses of TPO roof membranes are 45-mil, 60-mil, and 80-mil. (A “mil” is 1/1000 of an inch, it does not stand for “millimeter”). The thicker the material is, the longer the roofing membrane normally lasts, and the longer the warranty coverage will normally be.

A sheet of TPO roof membrane has three layers: a TPO polymer base, a polyester reinforcement fabric middle layer (called the “scrim”) and a TPO polymer top ply.

The main chemical component in a TPO roof membrane is propylene ethylene copolymer.

Loading new rolls of TPO roof membrane onto an old TPO roof
Loading new rolls of TPO roof membrane onto an old TPO roof before a roof replacement project

Heat-Welding TPO

TPO roofs are installed the same way that PVC roofs are, using extremely hot air to join the TPO sheets together to create a continuous waterproof barrier that covers the entire surface of the roof.

TPO roof membranes are thermoplastic, unlike EPDM roofing, for instance, which is thermoset. Thermoplastic means that you can always use heat (hot air at roughly 1000° Fahrenheit) to weld pieces of TPO membrane together for the life of the roof.

This heat is applied using either a hand-held hot air welding gun or a self-propelled automatic hot air welding machine (called a “robot” by TPO roof installers). The robot is used for the long seams in the field of the roof, while the heat gun is used for flashings and patches.

Heat welding is the proper way to seam TPO sheets together, to install TPO flashing, and to apply patches to the roof if it needs to be repaired.

The heat-welded seams in a TPO roof system are exceptionally strong, actually stronger than the rest of the TPO sheet.

Having heat-welded seams means that adhesives are not used to join the roof membrane sheets together, so adhesive failure and seam delamination are not problems for TPO roofs.

Unlike PVC, which is TPO’s main competitor as a white, cool roof membrane, the TPO roof membrane material does not rely on plasticizers to maintain flexibility over the life of the roof.

This means that the membrane does not lose flexibility over time because of plasticizer loss.

A hot air welding "robot" used for seaming sheets of TPO roof membrane together
A hot air welding “robot” used for seaming sheets of TPO roof membrane together

Typical TPO Roof Assembly

A typical TPO roof assembly consists of 1) the roof deck, usually concrete or corrugated steel, 2) a layer of insulation (commonly polyisocyanurate insulation) that varies in thickness according to local R-value requirements, 3) a cover board (most commonly gypsum board with a fiberglass facer), and 4) the TPO membrane itself.

TPO roof membranes are either fully-adhered, which means that the entire membrane is glued to the cover board, or mechanically-attached, which most often means that the TPO roofing sheets are individually fastened down into the roof deck using a line of fasteners which are hidden inside the heat-welded seams which join the sheets together.

installing polyiso insulation over a steel roof deck during a TPO roof installation
The first step toward a TPO roof system: installing polyiso insulation boards over a steel roof deck (image courtesy Carlisle SynTec Systems)

TPO Membrane Colors

All TPO roof membranes have a gray bottom ply, which nobody can see once it’s installed. A huge majority of TPO roofs are white, that is, they have a white top ply.

This is understandable, since a huge reason for using TPO is that it provides a reflective cool roof membrane, and white membranes are the most reflective.

TPO roofing actually comes standard from most manufacturers in more than just white. You can get TPO in white, tan, and gray from almost all manufacturers without it being a special order.

Many other custom colors are available as well, but you normally have to order enough of the material to make it worth the manufacturer’s while.

GAF, for instance, has 15 pre-formulated TPO colors, including green and red, but you need to order at least 40,000 square feet worth of membrane in order for them to make it for you.

A sheet of TPO during a roof installation, folded back on itself to show the white top surface and the gray underside.
A sheet of TPO during a roof installation, folded back on itself to show the reflective white top surface and the gray bottom layer.

TPO Roofing Solar Reflectance

One assumption that a lot of people have about colored TPO is that if the roof membrane isn’t white, it won’t be as “cool” and it won’t qualify for LEED points.

This is only partially true. The solar reflectance of tan TPO roofing, for instance, isn’t much lower than that of the white TPO. Colored TPO membranes can meet energy savings requirements and qualify for LEED points.

The initial solar reflectance (Solar Reflectance Index – ASTM E1980) for white TPO is 99. The initial solar reflectance is 86 for tan TPO. (And it’s 53 for gray TPO.)

And the 3-year aged (Solar Reflectance Index) for white TPO is 85, while for tan TPO it’s 77. (And 48 for gray TPO.)

These are numbers you can work with.

TPO Roof Repairs

If you aren’t a roofer who works with TPO, TPO roofing is one of the most difficult roofing materials to repair properly in accordance with the manufacturer’s instructions.

This is because of the heat-welding. Applying a proper TPO roof patch requires a specialized tool (the heat welder) and experience using it.

If your TPO roof is still under warranty, any repairs should be made by a roofing contractor approved by the manufacturer. You don’t want to give the manufacturer any reason to deny a future warranty claim.

Past improperly-made or unapproved repairs may be enough to void the warranty in some situations.

This goes for repairing items not even covered by the warranty, such as roof membrane punctures made by careless HVAC mechanics, for example. You still want a manufacturer-approved contractor to repair the roof.

If you have a preferred roofer who you want to use, you should call the manufacturer’s warranty department and check if it’s OK (it usually is). If you don’t have a roofer in mind, the manufacturer will give you the contact information of approved TPO roofers in your area.

If your roof warranty has expired, it’s a different ballgame. TPO roofing is among the easiest roofing materials to repair if you don’t need to do it as directed by the manufacturer for warranty reasons.

Although it’s still a good idea to have proper repairs made by a TPO roofing contractor, you can actually make most simple repairs yourself. You don’t need to use a heat-welder, or even TPO. Roof punctures, tears, or open roof seams can be fixed using third-party roof repair tape.

TPO is probably the most compatible single-ply roofing material there is when it comes to roof repair tape. Many roof sealant tapes use TPO as the protective backing on the tape due to its compatibility with the adhesive.

A roof patch made with a good repair tape can last more than 20 years, and if your roof is out of warranty, this probably means it will last as long as the roof.

If you want to repair your TPO roof yourself with repair tape, you’ll need to thoroughly clean the area with warm, soapy water and follow the instructions from the tape manufacturer. We talk more about using roof repair tape (and list the good ones) here on this page.

Using a handheld heat gun and a hand roller to apply a TPO patch
Using a handheld heat gun and a hand roller to apply a TPO patch

Popularity of TPO Roofing

TPO roofing is the single most popular type of roofing for new installations on flat (low-slope) roofs in the United States today.

40% of all new single-ply roof installations in 2019 used a TPO roof membrane, with that market share projected to increase over the next few years.

This means that right now, out of all new flat roofs in general, more than 3 out of every 10 are made out of TPO.

In the year 2000, almost nobody knew what TPO roofing was. The use of TPO as a roofing material has truly skyrocketed over the past 20 years.

So why is TPO roofing so popular now?

The popularity of TPO roofing has been driven mainly by a huge increase in demand for white (cool) single-ply roofing in the last 20 years. This demand is due to the savings on energy that a white roof membrane can provide by reducing building cooling expenses.

Stricter energy code requirements and the rise of LEED has made the use of white roof membranes practically mandatory in many places. But why TPO instead of one of the other white roofing materials?

In the early 2000’s, the consultants at our company knew all about TPO roofing as an alternative to white PVC and white EPDM for energy-saving cool roof installations. We also knew all about several serious issues with TPO roofing that had been identified both by researchers and by reports of real-life TPO roof failures.

We were not particularly satisfied by the reliability of TPO, and we continued to specify PVC and EPDM roofs for our clients.

Around 2010, we started to notice something curious. Whenever a client needed a roof replaced and we put the project out to bid, the contractors on our bid list started to pester us about maybe switching to a TPO membrane instead of whatever we had specified.

Eventually, we asked a few roofing manufacturer sales reps what was going on.

Apparently, there was a huge push among US roofing manufacturers to boost the volume of TPO roofing installations. The manufacturers wanted to make TPO a major part of their business because it was cheaper and easier to produce.

a sheet of TPO roofing at the factory
A 16-foot wide sheet of TPO roofing membrane at the factory (image courtesy Carlisle SynTec Systems)

They were offering commercial roofing contractors greatly reduced prices on TPO material, which in turn led the roofing contractors to start pushing TPO every chance they got. TPO suddenly meant significantly more profit per roof for the contractors even while they charged less for a roofing job.

As the contractors installed more and more TPO roofs, they effectively trained their crews to be TPO roof installers, which made them even more likely to recommend TPO to their customers.

The lower material price of TPO also made purchasing a new roof more attractive. More customers were willing to pay for a roof replacement instead of trying to keep their old roof going as long as possible. TPO roofing sales did, in fact, increase, and in a big way.

So that explains how TPO burst onto the scene.

A TPO roof is still less expensive than its competitors in the cool roof membrane market. It currently beats the other two types of single-ply roof membrane commonly used today, white EPDM and PVC membrane, on price.

In addition, many of our early concerns about TPO have been addressed by the TPO manufacturers – TPO roofing today is a much more reliable roofing material than it was in 2005 or 2010.

1. General: See this in-depth general article about various roof systems. It’s on the Whole Building Design Guide site, which is maintained by the National Institute of Building Sciences.

2. Building Codes: “R905.13 Thermoplastic Single-Ply Roofing” from the 2018 International Residential Code and “1507.13 Thermoplastic Single-Ply Roofing” from the 2018 International Building Code. Both available on the UpCodes website.

3. Chemical Compatibility of TPO: See this Chemical Resistance Guide for information about whether a substance will damage a TPO roof. The document is on the website of Roofing Products International.

4. Inspection of TPO Roof Systems: “TPO (Thermoplastic) Rooftop Guide/Inspection Checklist” is a handy two-page document put together by Carlisle Syntec Systems. It references Carlisle products, but it’s broadly applicable to other TPO systems.

5. Safety: See this material safety data sheet for health and safety information about TPO roofing at the GenFlex website. This is only an example and other products and brands may be different.

6. Technical: “Technical Advisory – TPO Single-Ply Roof Systems: Performance and Service Life” is an IIBEC paper from 2016 presenting “a general overview of information regarding the performance of thermoplastic polyolefin (TPO) single-ply membranes, to summarize general information related to the evolution of TPO single-ply roof membranes, and to provide general information to assist individuals with reviewing in-place existing conditions of TPO roof membranes”.  

7. Technical: See this TPO roof installation guide to see what’s going on in a typical TPO roof system. The guide is made available on the Johns Manville website.

8. Technical: See this product data sheet for the technical characteristics of TPO roofing at the Johns Manville website. This is only an example and other products and brands may be different.

9. Testing: “Testing TPOs (An unprecedented study shows surprising variations among TPO membranes)” explores TPO performance issues. The article appeared in Professional Roofing magazine in 2015.  

10. Manufacturers: See this list of TPO roofing manufacturers.