PVC vs. TPO: Is the Debate Over?

Over the last several years, it seemed as if TPO supporters have wanted to push the membrane onto every roof. Certainly the material has done very well and gained a large market share. But other membranes haven’t gone away, and some have a fairly stable market share. It’s easy to understand why single ply hasn’t done well on smaller roofs in urban areas, with their large numbers of penetrations and often chopped-up shapes; for these roofs, mod bit (or possibly a coating system) seems like an obvious choice.

What about PVC? It has a similar reflectivity to TPO and was the original weldable sheet. But there were questions about the plasticizers; what happens as they migrate out of the sheet? TPO was seen as being inherently flexible; over the years, it’s proven itself and has steadily improved in terms of weathering resistance. Manufacturers have been investing heavily in TPO but, surprisingly to some, PVC remains a viable alternative. In fact, we are starting to see investment in new capacity.

Let’s look at a comparison of the performance of the two sheets:

PVC_TPO-chart1[1]

In terms of weathering (i.e., based on the Heat Aging and the Accelerated Weathering tests), TPO has the clear edge over PVC. This may surprise some diehard PVC users, who may be unaware of the advances made in TPO formulation over the last several years.

While TPO has superior weathering and slightly better tear and break resistance than PVC, PVC does have some characteristics that certain customers need or prefer. For example, PVC has better chemical resistance; it does not absorb or get weakened by oils and greases. This means that PVC is the preferred membrane for restaurants and other buildings that have grease traps on the roof.

Also, PVC is slightly more flexible than TPO, which some contractors like. There used to be talk about welding differences, but both membranes weld well. TPO requires higher temperatures but, once a crew has adapted, welding is as straightforward as it is for PVC.

The following chart gives a snapshot of the overall performance of TPO versus PVC:

PVC_TPO-chart2[1]
So next time you’re debating which product would work best for an upcoming roofing job, it may be helpful to refer to the two charts above before you make your decision.

What do you think is the best roofing membrane: TPO or PVC? We’d love to hear from you in the comments below.

Related blogs:

PVC vs. KEE: What are the Pros and Cons?
How to Clean a TPO or PVC Roof
What are the Best Attachment Options for PVC and TPO Membranes?
Cool Weather Application Precautions for TPO and PVC

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  1. Jamie

    There are 4 types of PVC’s under ASTM 4434. I think you should qualify that your chart shows type II or III. PVC’s that meet ASTM 4434 Type IV still have much stricter qualifications than ASTM 6878.

    • Thomas J Taylor, PhD

      Jamie – thanks for the comments. Yes, I focused on Type’s II and III because they are far more common. Type IV sheet has a heavier weight reinforcing fabric and does have stronger physical properties as a result. In my view, single ply roofs don’t typically fail as a result of deficiencies in physical strength. The ASTM D4434 Type IV membranes have the exact same cap and core PVC layers as the Type II and III sheets. Best wishes for a successful 2015 roofing season!

  2. David Austad

    Which is the better roof depends upon configuration of roof structures building roof type and penetrations and any chemical usages.
    That being said I install a fair amount of Gaf 60 mil tpo for installation purposes tpo is much faster to install based on sheet sizes reducing seam footage by close to 50 percent compared to pvc and on top of that we are using the rhino bond attachment system which reduces labor costs even more.
    If your in the market to replace that old roof system let me show you how to save money and end up with a top of the line GAF TPO roofsystem with a 20 yr ndl warranty
    Best REgards
    David Austad Austadconstruction.com your gaf roofing and sheet metal contractor

  3. Thomas Berger

    Nice article. Bottom line, as an independent Consultant, we see PVC roofs that are performing well after 30 years. Recently we did a retrofit on a Laboratory Building with a PVC roof that was almost 50 years old and we patched and re-flashed new roof openings. They had no problem seaming to the original membrane.

    Most all TPO membrane, while less expensive, do not seem to have the longevity of the better quality PVC’s (such as a Sika Sarnifil PVC membrane). If our clients have to replace their roofs twice, or maybe three times in lieu of one installation of a good PVC roof, I consider the PVC option more green. To bad there is no current LEED points for that one.

    Not to say anything about the flammability of TPO. TPO is destroyed, while PVC stays intact. Interesting, yet un-scientific filed test https://www.youtube.com/watch?v=GySxn8egQpQ

    • Thomas J Taylor, PhD

      Thanks for sharing. There are definitely PVC roofs that have held up very well but some that haven’t. GAF has not had long term performance issues with TPO. At the end of the day, it’s about making the right choice of membrane and supplier for each situation combined with a quality installation. By the way, essentially all roof systems are required to meet FM and UL fire ratings. In the event of a fire, TPO has the advantage of not releasing any dioxins – that can’t be said of PVC. Best wishes for 2015!

      • Brad

        The only reason you are defending TPO is because it is what you produce and sell. PVC has been around for a long time, and as technology continues to advance with a large need/desire for “green roofing” TPO will remain to be what it currently is and pvc will exceed above. It’s just a matter of time. Try using tpo for a swimming pool liner (won’t hold up). PVC will reach a point of stability, and in fact already is, that tpo won’t be able to compete with. Also, price wise PVC will become less expensive as demands increase, leaving TPO on the back burner for good. With companies like Duro-Last, who continually push to improve their products to withstand all elements, flexibility, durability and weather conditions there really won’t be a need for dinosaur roofing like EPDM, multi ply, or TPO. Also, in your chart you’re comparing apples to oranges. You may want to consider your direction in engineering, unless you’re so close to retirement that it won’t matter. TPO roofs have a much higher maintenance cost than PVC as well. I fail to see how they are even comparable at all. tpo is more difficult to keep solar as it is not as easy to keep clean like PVC. TPO can only improve enough to stabilize itself as a cheaper choice than (why has there been no improvement on chemical durability/deterioration on TPO?) EPDM. Like I said though, PVC will continue to improve because chemistry will allow it to. (Elvaloy/ Ketone Ethylene Ester has been added to replace certain migrant causing plasticizers so UV rays do not cause damage as years past). PVC has already outperformed every roofing system out there over 50 years ago, yes in Germany, and it’s still holding up. TRUTH is TRUTH and cannot be disproven. No offense, but TPO is limited in it’s applications far more than PVC is, and has a 3rd life of proven performance than PVC.”Good luck this roofing season”.

        • Thomas J Taylor, PhD

          Brad – thanks for checking in with us. We have announced that we will be manufacturing PVC membrane in Cedar City, UT, later this year. Our goal is to support the roofing industry with a wide range of products that all meet or exceed industry standards. There isn’t a single “best membrane” for all situations. TPO has grown rapidly, but PVC is certainly a viable roofing option. Our goal is to offer a wide range of solid performing systems. Independent testing has shown EverGuard to have industry leading accelerated weathering performance, while EverGuard Extreme remains in a class by itself. Look for our GAF PVC later this year – this will help prove our commitment to the commercial roofing market.

    • Thomas J Taylor, PhD

      It sounds like you have a system that installs well for you. As you know, long term performance depends on installation and long term weathering. We’ve seen differences in the weathering performance of PVC depending on the manufacturer. Good luck in 2015!

  4. Owen

    Why is it that the TPO manufacturer’s have to make “advances – in TPO formulation over the last several years”?? Also, clarify why the ASTM standard for Heat Aging was increased in both temperature and days of testing several years ago? Admit it or not, many TPO membranes have suffered significant heat related failures in the recent past, thus requiring “reformulation” and modification to the ASTM testing. We (designers) understand that cost is always a factor in specifying of roof membranes, but longevity of reliable service life will serve the client, designer, and industry far better the lower initial cost.

    • Thomas J Taylor, PhD

      Thanks for your post. You’ve raised several questions, let me try to address them. First, you are correct, TPO has been continually improved since its introduction. As with any product, the TPO manufacturers have reformulated to take advantage of newer stabilizers that give better weathering. To demonstrate the improvement, the heat aging standard was increased. I think most people would agree that it’s a good thing whenever standards are improved or increased. Second, with regard to high heat failures, we have heard of (and seen) such failures in the lab and in the field. FWIW, we’ve never observed such a failure in GAF’s EverGuard TPO membrane. But the potential for heat related failure remains under certain conditions (that’s one of the reasons why we developed EverGuard Extreme TPO, but that’s a discussion for another day). Traditional PVC membranes can also suffer from significant plasticizer loss (and premature failure) in high heat situations. Some PVC manufacturers are now using newer KEE plasticizers. I don’t view this as a negative – better roofing membranes should be a goal of all of us. Good luck in 2015!

      • Bob Roofer

        Weather Resistance: So are you saying recent improvements in TPO roof membrane chemistry is why ASTM chose to increase the D6878 minimum standard? Not that ASTM increased the minimum requirements because of the issues with heat aging on TPO and failures?

        Why is there an exclusion for coverage on GAF TPO warranties as follows “8. Exposure to sustained high-temperature conditions; however, for
        systems utilizing EverGuard Extreme® TPO membrane, exposure in
        excess of 195°F.”

        • Thomas J Taylor, PhD

          Bob – good questions. I think there has been some industry confusion on these points, so I’ll try to clarify. The ASTM minimum heat aging specification was raised because of issues with some TPO membranes that were failing due to high heat. Most of these were early versions. Examples were membranes in the west at high altitude and southern roofs were some membranes were failing close to the parapet wall where heat was being trapped. GAF has always strongly supported efforts to toughen the TPO specification and our membrane has always performed well. Our EverGuard Extreme membrane was developed to handle very aggressive heat/sunlight situations and situations like solar panel installations. The latter are dark and absorb a lot of heat – raising roof temperatures a lot. Our standard membrane is one of the best performing TPO sheets, but for solar installations and other demanding situations we recommend EverGuard Extreme. I encourage you to check out our blog on the history of TPO and another on TPO formulation facts.

          • Thomas J Taylor, PhD

            Bob – if you read manufacturers’ specs or application books you’ll find that PVC typically has limitations between 140 and 150F. It makes sense because the plasticizers are relatively volatile at elevated temperatures. TPO is inherently flexible and therefore doesn’t contain plasticizers. Having said that, both materials are excellent choices, depending on the location, building specifics, and contractor experience. We provide both PVC and TPO membranes and have good contractor training programs available.

      • David

        RE: “FWIW, we’ve never observed such a failure in GAF’s EverGuard TPO membrane.”

        What about the Allan Buick & Bers 2011 Study on the roofs at UNLV in Las Vegas that found high heat related failures of a 3 year old GAF TPO roof that resulted in replacement only 3 years later (2008) with a GAF TPO that was also failing only 2.5 years later? The study also found a 7 year old GAF TPO with cracking membrane at the seams and deterioration in the field of roof with no additional UV loading from adjacent reflective surfaces.

        This is, of course just one example, that happened to receive a lot of notice. It seems misleading, at best, to state that GAF has not observed pre-mature failures of their TPO membranes when it is well documented. And following Bob Roofer’s comments below, with regard to the heat restrictions in the warranty, if there were no observed issues, why exclude “high temperature conditions” (and especially with no definition of what those conditions are) from the warranty?

        While re-formulations and testing standard revisions may have improved TPO performance in recent years, wouldn’t we all feel more comfortable with the product if TPO Manufacturers would own up to the issues and the corrective measures taken to address them? Instead it seems like all TPO manufacturers will continue to dodge the issues, spin the data, blame “other manufacturer’s” products for the failures, and protect themselves against unproven performance with vague and misleading warranty language…

        • Thomas J Taylor, PhD

          Thanks for your comments. GAF has addressed the Allana, Buick & Bers 2011 observations in presentations at several industry meetings. Their study didn’t involve forensics as to what the root causes were – our own investigation, as part of our regular roof inspection program, found that the issues were due to a particular adhesive, no longer in use in the industry.

          All TPO manufacturers list temperature limits either in their warranty or in their spec books. We regard 160°F as an upper limit for standard TPO and sustained temperatures of up to 195°F for EverGuard Extreme.

          GAF has led the industry in showing that high heat situations can be challenging for some TPO membranes. In fact, our EverGuard Extreme was designed for high heat and demanding applications where long warranties were required. We are proud of the performance of our EverGuard and EverGuard Extreme membranes, as demonstrated in a large independent study and over 1.5 billion square feet installed. As you noted, TPO has continually improved and is now the largest low slope membrane in the US. All roof membranes have different strengths and we support roof consultants, specifiers, and other roofing professionals in selecting the best membrane for each situation.

  5. OP

    Well my seller line used to be” TPO they make frigging figher jets out of this stuff “!! Lol …,, greetings from atlanta ,ga;-)

  6. Gerald B. Curtis

    Although I have not seen this personally, information from credible New Mexico contractors report several instances where cracks about an inch away from and parallel to welded seams of fully-adhered, fleece-back TPO membranes have appeared. These appear to be manufacturer-independant occurrences.

    Gerald B. Curtis, RRC, RRO

  7. Wayne Scholten

    Thomas, I will only speak from real life experience. Over the past 10 plus years I have been called out on and evaluated numerous pre-mature TPO membrane failures, and not one PVC membrane failure.
    Maybe someone else is getting those calls? The TPO membrane failures are not partial to any particular manufacturer. Recent failures have been on 60-mil TPO’s that have rapid polymer deterioration at high heat or reflective light onto the membrane. Sun light bouncing off walls or skylights.

    That being said, I think the TPO formulation ‘growing pains’ will eventually work themselves out, who knows when?

    • Thomas J Taylor, PhD

      Wayne – thanks. We are aware that some brands of standard TPO have experienced premature failure in the past, including in high heat or reflected light applications. (I can say with certainty that I have not seen any such failures with GAF’s standard TPO to this point, and I have been here for 8 years.) Some of these failures are likely from earlier formulations. There is no doubt that the manufacturers have continued to improve their formulations, but there are sheets that have been doing well for many years (we know that ours has, based on the lack of guarantee claims and other corroborating evidence). There is also our EverGuard Extreme TPO, which was designed for high heat applications and has proven to outperform under those adverse conditions. As for PVC, loss of plasticizer over time is definitely a concern, and that makes it stiffer and, ultimately, more susceptible to cracking. That doesn’t mean it will fail earlier than expected, just that you always need to go with a reputable supplier who designs the sheet to go to the full warranty length.

      • MKT

        Started in the year 2000 with TPO 45mil and still installing TPO but minimum thickness 60mil. We experianced complete faillure with 45mil after 7-8 years and with darker colors even faster. Believe however that present formulations have approved signifently.
        PVC experiances in the urly days 30- 40 years ago same problem when using 40-45mil thick membranes, and I remember that you could hear the PVC membrane craking o snattering. Non migrating plasticicers and anough thickness gives longer life span.
        Regards,
        C.S

        • Thomas J Taylor, PhD

          Chris – thanks for checking our blog site. Today’s membranes, both PVC and TPO, perform far better than when they first came out. Our EverGuard membrane has been shown in a large independent study to be one of the best performing TPO materials and EverGuard Extreme to be in a different class. Extreme was designed for demanding situations and is proving to be a very strong performer.

        • Pat

          The PVC sheets that cracked were Trocal without a reinforcement scrim. A terrible experiment that went horribly wrong. That said, there are 30+ year old Trocal roofs in the Burlington, VT area that were installed at the same time and perform well to this day.

          • Thomas J Taylor, PhD

            Pat – good comment. A reinforcing fabric or scrim has proven to be essential. Some membranes are generally recognized as not performing well, although there are sometimes examples that are holding up after many years. We believe that both good design and consistent manufacturing go a long way to reducing the risk of roof issues.

  8. Cool Flat Roof

    Back to Qwen’s and Wayne’s questions, and to advance the thought.

    1) How does a client know which “generation” of TPO they are getting … even GAF is not branding their membrane as Gen 1, Gen 2, Gen 7, etc.

    2) Since you (GAF) produce / sell both TPO and PVC, when / why was a decision made to pronounce TPO the king and sweep PVC under the rug?

    3) How many generations of TPO has GAF produced?

    Are newer GAF TPO products compatible with old / original membranes?

    Are all TPOs compatible with each other – can you weld old Carlisle to new GAF or any other combination of manufacturer and generation?

    Thanks, Leo

    • Thomas J Taylor, PhD

      Leo – thanks. I’ll answer all your questions, but in a different order:

      1. When repairing a TPO roof, the procedure is the same as with PVC that your company is familiar with. Old TPO can be repaired with new material if the surface is prepared correctly. Always do a test weld to determine the right welder settings and technique.
      2. TPO roofs that are under warranty have to be repaired with our membrane to maintain that warranty. We believe that our membranes perform better than any others, so we don’t see why anyone would repair a GAF roof with another membrane.
      3. GAF has over 1.8 billion square feet of TPO installed. We haven’t seen any systemic issues with our membrane since it was introduced in early 2002. In 2011, we introduced a new generation, EverGuard Extreme™, designed for both longer life and very demanding situations. It carries warranties as long as 35 years, depending on thickness and installation method.
      4. Whenever you buy our standard TPO you can be assured that you are getting one of the best performing membranes in the industry. We invest heavily in testing and have the most advanced manufacturing plants to ensure high consistency.
      5. You are correct in that we carry both TPO and PVC membranes. As I said in the blog, both have their place – there are plusses and minuses of each.

      • Brad

        TPO is cheaper to produce, that’s why PVC was put on the back burner. In 2003 (one year after TPO roofing was introduced)Global Development and Environment Institute did a research study in attempt to try to phase out PVC.

        This was also during the beginning of the “Go Green” explosion, which is still big, but has calmed down since then. So in this I will suggest that many companies developed TPO roofing systems in lieu of this “phase out PVC” as an alternative product to PVC roofing. Well, PVC is still here, highly recyclable, and (after production) earth friendly. However, PVC is nearly twice the cost to produce as TPO while the profit manufacturer’s and distributers make is nearly twice as high as that of PVC due to the low production cost even though TPO is cheaper to the consumer than PVC. This is why TPO has become the fastest selling roof in the U.S. not because it’s a better or even equal product, but because it is a “cash cow” no matter who the manufacturer.

        If you’re going to choose a “green roof” choose PVC. It’s slightly more than TPO when purchased, but with lower maintenance costs over a 15-35 year warranty period, and beyond.

        Now, where is GAF’s products made? PROUDLY in the USA! I’m not at all knocking their products. I am suggesting that PVC roofing be strongly re-introduced again by GAF. It’s a difficult task and expensive journey to manufacture here in the USA, it’s no wonder they sell TPO over PVC. But, who’s first here? The customer should be the true scope of GAF’s focus, not their already insanely high profits. It’s a bit irritating to see a company swear by a product they KNOW is not as good as another, and try to “white-lie” their way around it. Just be honest! It’s NOT as good of a product as PVC, it just makes more money. I suppose that makes perfect sense considering the division of GAF that makes sheet goods filed for bankruptcy and bailouts in 2001 to make a product that would help recover losses. But I think it is time to hang up the TPO line and get back to the PVC engineering and production. EDPM and TPO need to become a thing of the past. It’s time to move forward. It makes no sense to continue to attempt to improve a product when after 14 years it still deteriorates from chemicals, natural salt, solar, and acid rain.

        • Thomas J Taylor, PhD

          Brad – thanks for checking in with us. Yes, we are very proud to be a manufacturer here in the USA. Also, we have announced that we will be manufacturing PVC membrane in Cedar City, UT, later this year. Our goal is to support the roofing industry with a wide range of products that all meet or exceed industry standards. TPO has grown rapidly and we support the market with our GAF EverGuard and EverGuard Extreme membranes. Independent testing has shown EverGuard to have industry leading accelerated weathering performance, while EverGuard Extreme remains in a class by itself. As you note, PVC is a very viable roofing option – look for our GAF PVC later this year.

  9. Patrick

    In terms of weathering (i.e., based on the Heat Aging and the Accelerated Weathering tests), TPO has the clear edge over PVC. This may surprise some diehard PVC users, who may be unaware of the advances made in TPO formulation over the last several years.

    While TPO has superior weathering and slightly better tear and break resistance than PVC, PVC does have some characteristics that certain customers need or prefer. For example, PVC has better chemical resistance; it does not absorb or get weakened by oils and greases. This means that PVC is the preferred membrane for restaurants and other buildings that have grease traps on the roof.

    Also, PVC is slightly more flexible than TPO, which some contractors like. There used to be talk about welding differences, but both membranes weld well. TPO requires higher temperatures but, once a crew has adapted, welding is as straightforward as it is for PVC.

    The following chart gives a snapshot of the overall performance of TPO versus PVC

    ^^^^^^^^^^^^^^This is incorrect as when you weld TPO you use a lower temperature to not melt through the membrane while with PVC if your not smoking your not welding!

    • Thomas J Taylor, PhD

      Thanks. Yes, good manufacturers have taken advantage of advances in the technology and today’s membranes are better than ever. I agree with you that TPO and PVC weld differently. Remember to always do test welds at the start of the day and whenever conditions change.

  10. Mike

    Whenever I hear the term reformulated related to a roofing product, it’s time to run. A product that has stood the test of time doesn’t need to be “reformulated” nor should it be. I’ll stick with my PVC and its long standing 30+ years of proven reputation. GAF can reformulate TPO all they want, but past history and proven proformence are more important to me.

    • Thomas J Taylor, PhD

      As improvements become available most responsible manufacturers will take advantage of them. Although PVC has been around for a long time, there isn’t a single formulation out there that hasn’t been changed. Often standards and specifications get increased and so a manufacturer makes improvements to the formulation to meet those new requirements. Sometimes it’s simply the marketplace that asks for better performance. Think of your truck or cell phone – would you be happy sticking with these as they were made decades ago? We have improved our TPO, with proprietary technology being added to our EverGuard Extreme making it the best performing TPO on the market.

  11. RAD

    I am looking to replace my old tar and gravel roof on a low slope 2 storey semi-detach house. I really wanted to stay away from the torch down roof, and was thus looking at TPO roof. Many contractors advertised that they are GAF master elite roofers, yet only want to install torch down materials. Any advice/input would be greatly appreciated. I have had estimates for the torch down roofs from $3,600 – $10,000, and the TPO estimate was $9,000. One person wanted to do the GAF self stick membrane for $9,000 and another said shingles for $7,000. I am really confused, as I want a good product that will last, need to make a decision by this week. Thanks, Rad

    • Liza Barth

      Thanks for the interest. We’d recommend that you look for a GAF Master or Master Select roofer for advice (http://www.gaf.com/Roofing/Commercial/Contractors/SearchByPostalCode). They work more on the low slope side – our Master Elites, who you might have been talking to deal primarily with sloped residential and focus on shingles. While TPO is a great option, it lends itself more to large roofs like big box stores. Good luck with your project!

    • Thomas J Taylor, PhD

      Gary – thanks for checking in with us. When you put salt on a TPO roof, make sure you don’t walk over it – salt is fairly abrasive and sharp and walking on it could damage the TPO surface. Other than that, it won’t cause deterioration of the TPO. I’d be more concerned about the drains. In the future try to use one of the alternative products based on magnesium chloride – it might be a little kinder to any metals in the drain system. As a general comment – roofs are best left alone except for periodic inspections and the like. The less traffic the better.

      • Gerald B. Curtis

        Since NaCl is hygroscopic, even deliquescent under the right conditions of high humidity, I question if after a few minutes, any really sharp and abrasive edges/corners would remain POSSIBLY to do damage to a TPO membrane subjected to causal foot traffic.

        deliquescent
        becoming liquid or having a tendency to become liquid.
        CHEMISTRY
        (of a solid) tending to absorb moisture from the air and dissolve in it.

        MgCl might be gentler to the drain body metal, however, and I like the idea of avoiding all unnecessary roof traffic.

        • Thomas J Taylor, PhD

          Thanks for the comments. It is important to make sure that the areas around drains are not impeded for buildings in areas that might expect large snow storms. Although rare, there have been examples of snow and ice build-up that have led to roof collapse. My comments about avoiding damage to the roof surface are common sense – and, yes, salt does absorb moisture fairly quickly. My point about avoiding damage to the roof surface was aimed at the brief time while the salt is being applied. Some roofing companies have developed a winter business of clearing snow and ice away from roof drains on large commercial buildings. It may be worthwhile evaluating their services in your area.

  12. Richard Chodera

    We have a TPO roof system with Polyiso and DensDeck coverboard in place. There were some previous leaks that were not immediately repaired. I am interested to know GAF’s policy on how much moisture is acceptable to leave in the polyiso profile when replacing the affected areas?

    • Thomas J Taylor, PhD

      We supply materials and are not roof designers. So, the local roofing professionals would need to be consulted for guidance on the specific situation you have. Having said that, a roof scan will highlight the areas that need to be investigated. If any liquid water is present then the affected insulation should be replaced. Decisions on other levels of moisture should be made by a local professional and/or roofing consultant. They would consider the amount of moisture, the size area affected, and the overall roof system. If the roof was covered by a GAF warranty, we would need to have an inspection performed because any remediation would depend on many factors beyond just the moisture level. We very much want to see roofing systems perform – thanks for checking in with us.

      • Richard Chodera

        So the presence of moisture in the Iso seems to indicate some thermal heat transfer through infrared, and we have seen old growth on the sheets as well. As a performance system, does GAF have any opinion about those two consequences of moisture being trapped in the iso layers? Long term detriment to the products being warranted?

        Thanks

        • Thomas J Taylor, PhD

          Thanks for following up. Yes, moisture within insulation is generally considered as being detrimental to thermal performance. Our products meet or exceed all required industry standards, but for guidance on any roof system you need to consult with a roofing design specialist. Each roof is unique and an actual inspection would be needed by a roof consultant or specialist to determine the best path forward.

  13. Margaret Fukunaga

    I am interested in a TPO roof for energy efficiency. However my insurance company is looking for the hail resistance “class”. They would like to see a class 4. Does anyone know this for a residential TPO roof?

    • Thomas J Taylor, PhD

      Single ply membranes such as TPO are rarely used for residential construction and are not used for pitched roofs. I would guide you towards our Timberline® ArmorShield™ II Shingles which do have a Class 4 hail rating. In addition, more reflective shingle colors are available for energy efficiency. I would suggest that you consult with a GAF certified contractor for more information. Thanks for reaching out to us – good luck with your project.

        • Thomas J Taylor, PhD

          Margaret – thanks for the comment. Yes, absolutely, TPO roof membranes do reflect a significant amount of heat back into the sky leading to less heat build up. TPO is very resistant to standing water, but if the roof surface isn’t pitched towards drains then you can get dirt build-up over the course of months during wetter seasons. That dirt leads to lowered reflectivity which reduces the energy efficiency. Also, flat roofed mission bungalows have parapet walls around the perimeter that reflect heat down onto the roof surface. Make sure that your TPO is designed for high heat / severe sun conditions that are seen in the west. Not all TPOs are the same and I would recommend GAF’s EverGuard Extreme which was designed for demanding situations. Take a look at TPO Independent Study to see more details about this product. Thanks for checking in with us.

  14. Dan Aware

    I need to replace a 30 yr old exposed fastener metal roof on a pre-engineered warehouse. The roof has about a 3/12 pitch, minimal penetrations (only plumbing stacks, no A/Cs), but requires several laps of the metal sheets due to size. It is located in FL a few miles from the east coast – lots of sun heat and salt spray, but no foot traffic or chemical/grease exposure. Several roofers have recommended a TPO overlay. A roofing consultant suggested PVC would be better. Two other roofers suggested metal replacement (one suggesting standing seam replacement). Which of your products would you recommend?

    • Thomas J Taylor, PhD

      There are really two answers to your question. Purely from a product perspective, I would recommend TPO as the best roof membrane for your area. Some TPO membranes are more resistant to high heat and UV exposure such as you get in Florida so you should consider GAF’s EverGuard Extreme which is the best TPO membrane available today (take a look at Independent TPO Study ). A good TPO membrane will withstand the conditions you list, but we also need to consider your existing roof system. A TPO membrane could be overlayed by filling in the metal flutes with polyiso insulation, followed by a cover board. But, you would need a roofing professional to evaluate the existing metal roof, taking note of its condition and design. I would urge you to reach out to a local GAF commercial roofing representative as a next step. Good luck with this project and thanks for checking in with us.

  15. Alan Smith

    In Florida, when you wrap the 60 mil GAF TPO over the roof edge and terminate with an aluminum terminatoin bar and screws, it splits open between 6-8 years where it goes over the edge. It happened on my flat Den roof and a lot of manufactured homes that I have come across. The sun makes the plasticizers come out, it thins and becomes brittle and splits. The only manufacturer that backs a warranty in Florida is a PVC manufacturer. After one summer, you wipe your hand on TPO and it turns white from plasticizers that came out of the material. This does not happen with PVC.

    • Gerald B. Curtis

      Plasticizers in TPO? I was going to write that you were confusing the need for plasticizers in PVC Membranes with the no-need arising from the quite different chemistry of the TPO Membranes that I thought required none.

      However, in the case of GAF’s TPOs, I would have been wrong. While other manufacturers specifically state that NO plasticizers are used, a GAF Technical Representative, and indeed GAF’s own TPO Product Information literature, both confirm that no LIQUID, but, instead, SOLID plasticizers are used.

      I am not questioning your observation of TPO splitting on a parapet edge (if, indeed, it is TPO of which you write) since a particular manufacturer’s TPO splitting has been observed under VERY specific circumstances in one of the Southwestern States, but your case may not be a viable example of this phenomenon.

      Perhaps Dr. Taylor will respond, throughly explaining the need for ANY plasticizer in GAF’s TPOs.

      • Thomas J Taylor, PhD

        Gerald – I can assure you that TPO roofing membranes do not contain plasticizers of any kind. TPO is inherently flexible – that is one of it’s advantages. Without visiting the roofs that are being discussed it’s difficult to say what might have happened. However, because TPO doesn’t contain plasticizers it is generally better suited to warmer / high sunlight conditions. Our GAF EverGuard Extreme TPO is specifically designed for high heat / sunlight and should be given strong consideration for demanding applications. Thanks.

    • Thomas J Taylor, PhD

      Alan – this is not something that we have seen happen.It could be that the TPO is being severely creased during installation, but again – we haven’t seen the cracking you describe. PVC is more flexible and maybe that makes it a better choice for your application. There’s no doubt that Florida has very high sunlight and heat exposure – you want to select a membrane that performs above average for this type of location (take a look at the Independent TPO Study for more information). Also, one huge advantage of TPO is that it doesn’t contain plasticizers. In severe conditions, earlier TPO can chalk – that’s the white pigment coming loose at the surface as the TPO starts to erode. Thanks for checking with us.

  16. Rob

    In 2003 I had a .60 mil epdm roof with insulation board installed on a flat roofed retail building and have nothing but problems. Water ponds in several areas as there is no roof pitch. I’m looking into covering the epdm with TPO or PVC. How does your Everguard Extreme TPO hold up in ponding roof situations as compared with PVC and are ponding situations covered under warranty?

    • Thomas J Taylor, PhD

      Rob – both TPO and PVC hold up well in ponding water situations. TPO is used as a pond liner, proving that it doesn’t degrade with water. PVC contains materials that can be food sources for algae and mold – so if water is present on a frequent basis I would steer you towards TPO. Our GAF EverGuard Extreme is specially formulated for demanding locations in terms of weather resistance and it’s very resistant to high sunlight and heat loads. We do not exclude ponding water for our TPO, but I would encourage you to discuss the specifics of our warranty with your local GAF representative.

      In situations where the roof has no pitch its good practice to install tapered polyiso insulation – this provides slope towards drains. Again, talk to your local GAF representative about this option – we have a tapered design service. Good luck with your building.

  17. James Newton

    I’m looking to install GAF TPO 60 on a tapered roof that will hold water at the perimeter almost continually. The roof flashing will have a lip on it that dams water about 12 to 18 inches wide at the perimeter. The ponding water will be present almost daily because of morning dew condensation on the TPO. Rain will also pond at the edges. Is TPO the best option for a roof that will have tapered insulation but that will hold water at the edges?

    • Thomas J Taylor, PhD

      Jim – TPO is generally not affected by standing water, however there are two cautions you should think about. It is never good roofing practice to have a roof design that will have standing water for significant periods of time. You need to consider the flashings and any penetrations and also depending on the location what might occur during freezing temperatures. Secondly, standing water tends to attract dirt and debris, resulting in the membrane getting a dark layer of that dirt etc. That can lead to heat build-up. If at all possible, look at how to put in slope towards the drains. It would be worth talking with a local roof consultant about your unique situation.

    • Thomas J Taylor, PhD

      William – on a single ply roof such as TPO, fishmouth is a term often used to describe a weld that’s partially opened up along a seam. So, the seam might not have failed, but the heat weld doesn’t extend all the way to the edge of the membrane in an area that might be a few inches long. If it wasn’t caught during an initial inspection the TPO sometimes starts to lift up over time, hence the term fishmouth. Also, if the welder wasn’t set up correctly, occasionally the top sheet gets pushed along a bit and scrunches up to form a small gap in the edge of the weld every now and then. I don’t hear the term fisheye with respect to TPO but I think it’s a small gap in the edge of the weld while a fishmouth is larger. In both cases, the weld might be fine, but the opening along the edge needs repairing for long term assurance of roof performance. I would recommend that you discuss this with a membrane manufacturer’s local technical service representative if you have concerns. But TPO welding defects along the edge can be repaired without issue.

    • Thomas J Taylor, PhD

      TPO is definitely an excellent performing roof membrane but PVC does have its place. You might also be interested in our blog about the history of TPO.. Thanks for checking in with us.

  18. Christina

    Hi Thomas,
    Thanks for the above article. I have a residential home located in Southwest Florida that needs to be re-roofed. There are two areas of the roof that are flat: roof above garage (22′ x 26′; 572 sqft) and a section that is part of our living area (13′ x 19′; 247 sqft).

    I recently was quoted with Polyglass APP for the flat roofs which from my research seems to be a Modified Bitumen material.

    I want the best material (longest life) to be installed on my flat roofs and trying to figure out if TPO is better to go with. From the little research I have done, it sounds like TPO in Florida is superior to Modified Bitumen. However… you write:

    “It’s easy to understand why single ply hasn’t done well on smaller roofs in urban areas, with their large numbers of penetrations and often chopped-up shapes; for these roofs, mod bit (or possibly a coating system) seems like an obvious choice.”

    (1) What is considered “smaller roofs”?
    (2) What do you mean by “large numbers of penetrations and often chopped-up shapes”?

    I guess I am trying to find out whether or not my two flat roofs meet the criteria for a TPO installation… or am I better off with Mod Bit?

    Thanks,
    Christina

    • Thomas J Taylor, PhD

      Christina – thanks for checking in with us. In general, heat welded membranes such as TPO are best installed on large roofs, significantly bigger than you have. Think in terms of a local big box retailer or larger. Having said that, we know of far smaller roofs that have TPO installed with no issue. The higher reflectivity can noticeably reduce the summer heat load on any building. In terms of “penetrations and often chopped-up shapes” think about tall apartment buildings and the like. They have smaller roofs but there are often lots of vent stacks that penetrate through the roof. Also, older multi-story apartment buildings in urban areas frequently have irregular shaped roofs. These situations make for difficult installations of heat welded membranes such as TPO. I would encourage you to talk to a local GAF Factory-Certified Elite® Roofing Contractor for more specific advice for your situation.

  19. Don Clark

    My condo has a flat (slight slope) roof with a bright white membrane. The color appears to be molded into the membrane material and not painted. Based on this I assume the membrane is TPO or PVC. I have a technical background, but no expertise in roof membranes.

    There are a few small patch areas that a roofer has identified as dissimilar material patches. These areas appear to be heat or solvent welded. The roofer recommended replacing the entire membrane. This seems unnecessary since there is no sign of leakage externally or in the building interior. The condo was built in 2005 and is located in San Francisco so the roof is at most 11 years old.

    There is so much local demand for construction, that the condo association is unable to get competitive quotes. Can TPO and PVC be solvent or heat joined? If these materials cannot be joined, how could these patches be chemically dissimilar?

    • Thomas J Taylor, PhD

      Don – assuming the roof is either TPO or PVC, the patches should be the same. If you suspect they are not, then they must be glued on which is not a good solution. Small punctures of either membrane are repaired by heat welding a patch of the same material over the damaged area. I can’t comment on the best way to proceed without a lot more knowledge of the roof condition. You should consult with a GAF Master Select™ Roofing Contractor – they specialize in low slope roofing systems and will be able to give specific advice.

      • Don Clark

        Thanks Thomas. We have been unable to interest San Francisco roofing contractors in looking at small jobs. Is there a guide I could use to ascertain materials and joint technique myself?

        • Thomas J Taylor, PhD

          Don – I’m not aware of any such guide. It’s possible that a general building maintenance contractor could help. You might want to consult with other condo associations to see how they handle jobs of this size.

    • Thomas J Taylor, PhD

      Alan- thanks for checking in with us. In general, the roofing industry regards TPO as one of the most cost effective membrane options. Also, some TPO membranes that are available demonstrate excellent performance in accelerated weather resistance testing. If that translates to long term performance in the field, then that too would add to the value of installing the right TPO membrane. In hot climates such as yours, care needs to be taken if you are specifying PVC. Plasticizers get driven out of PVC membranes by heat and, as for TPO membranes, some are more resistant to this effect than others. Good luck with your projects.

    • Thomas J Taylor, PhD

      Joe – no, PVC and TPO can’t be welded together, they are two very different polymers. Imagine trying to weld steel and aluminum together! This means that during a repair its very important to figure out what the membrane is. On an older roof sometimes there are no longer records of what was installed and the owner doesn’t know. In that case, a contractor might have to resort to trying to weld on a piece of TPO and a piece of PVC. For each piece, the right cleaning procedures should be used for the existing membrane. Whatever welds will tell you what the original membrane is.

  20. Lynn

    We use PVC and TPO and we’ve found it very difficult to determine which is which. Is there/are there some relatively easy and quick methods to identify PVC vs TPO?

    • Thomas J Taylor, PhD

      Hi Lynn – unfortunately there isn’t a quick and easy way to distinguish between TPO and PVC. Membrane age and condition can make this quite hard. For a roof that is in need of repair, some contractors will clean a small area and try to weld PVC and TPO to the membrane. TPO won’t weld to PVC and vice versa. Having said that, an experienced commercial roofing contractor can generally tell by walking the roof and closely examining the surface in most cases.


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