Changes in PVC technology over the years have produced stronger, more flexible membranes

— By Rita Tatum, Contributing Editor

Roofing and reroofing of commercial buildings generally reflect the overall economy. Growth for the first six months of 2001 is at best flat and at worst down a few percentage points. The exception to that rule, however, is in thermoplastics, where shipments are up more than 16 percent for the first six months, according to industry data.

Essentially composed of TPO and PVC membranes, the thermoplastic market continues to buck the trend. PVC membranes account for about 55 percent of the thermoplastic shipments during the first six months.

“Because of economic conditions around the world, the roofing industry in general is down,” explains Tom Hollingsworth, president of Duro-Last. “But thermoplastics have enjoyed a huge increase already this year.”

Installed costs for PVC roofing membranes range from about $1.28 to $1.89 per square foot, according to R.S. Means’ 1999 data, which allows them to compare favorably with EPDM on costs.

Vinyl roof membranes were introduced in the United States in the 1970s. The concept caught on because these single-ply membranes offered a clean, safe, energy-efficient and cost-effective solution, while also providing design flexibility.

In Europe, vinyl single-ply membranes were being used extensively in the 1970s. As they gained popularity in the harsher U.S. climate during the mid to late 1970s, formulations and installation techniques were fine-tuned by both American and European companies.

Some of those initial vinyl roofs remain in service today. Though the specifics of PVC membranes vary from manufacturer to manufacturer, they share some basic characteristics. According to the Single-Ply Roofing Institute (SPRI), PVC membranes are generally reinforced and often are light colored and have a high resistance to fire, bacterial growth, industrial chemical atmospheres, root penetration and extreme weather conditions.

Early formulations used stabilizers and plasticizers to provide flexibility and ultra-violet resistance. “Newer formulations have incorporated other polymeric additives to achieve the same results,” says SPRI.

“Many of PVC’s attributes are achieved in the compounding,” says Paul Oliveira, thermoplastics product manager for Firestone Building Products. How the polymer is built and how reinforcement materials are used help define the PVC membrane’s flexibility and other attributes.

The success of PVC membranes in the market can be attributed to a range of factors. One is that they can be heat-welded so that seams are extremely strong. What’s more, the basic makeup of vinyl is fire resistant. Vinyl roofing membranes self-extinguish and resist flame spread.

“PVC roofing also is lightweight compared to built-up roofing,” points out Tom Gallivan, marketing manager for Stevens.

PVC is also well-suited for some conditions that can damage other roofing systems. “PVC roofs have high chemical resistance, particularly to animal fats and greases,” says Jim Burkett, national product and marketing manager for GenFlex.

Urban Heat Island
White and light colored roofs offer facility executives a way to reduce a building’s cooling load as well as to help the environment around the building. Scientists at Lawrence Berkeley National Laboratory (LBNL) have documented that heat gets trapped in cities’ concrete and asphalt. About half of U.S. citizens live in urban heat islands, where the temperature can be as much as 5 degrees hotter than in the nearby countryside, where trees and vegetation help to reduce afternoon heat.

To demonstrate the effect of roof color on the urban heat island effect, Jeffrey C. Luvall and Dale Quattrochi from NASA’s Global Hydrology and Climate Center used a specially equipped airplane to record photographic and thermal infrared images of Salt Lake City. As predicted by LBNL research, dark-colored roof surfaces were shown to be absorbing solar radiation, thus indirectly intensifying the urban heat around them. In contrast, a large distribution center with a light-colored roof was nearly undetectable to NASA’s heat-sensing instrumentation.

“Quite honestly, because of its reflective properties I didn’t know that the building existed until the day I was escorted onto the roof,” comments Luvall.

Many vinyl roofing membranes have reflective surfaces, which reflect the sunlight and radiant heat away from the building. Reinforced thermoplastic vinyl has scored more than 104 on the Solar Reflective Index — off the chart on a scale that is designed to measure the relative reflective and thermal emissive performance properties of roofing surfaces on a scale of one to 100. That’s why a number of PVC membranes are recognized by the Energy Star Roof Products Program of the Environmental Protection Agency.

In addition to helping the environment, PVC membranes can help green the company’s bottom line, according to Jon Gardner, GAF marketing director for low-slope products. “Energy savings are significant,” says Gardner, who worked through the numbers using formulas on the Oak Ridge National Laboratories Web site. “For example, in Miami a 500-square (50,000 square feet) PVC roof can save as much as $55,000 in energy costs over 15 years.”

Recycling and Repairs
PVC roofing can be removed and replaced with little or no release of airborne contaminants. During installation, fumes and odors are minimized as well because the membranes are hot-air-welded.

When removed from rooftops, PVC is being turned into speed bumps, parking curbs and asphalt patching material. In addition, vinyl roofing manufacturers may turn what little post-industrial recycled roofing scrap is left from the manufacturing process back into some membranes.

Vinyl roofing membranes also are being used on urban rooftop gardens, which consist of a multiple layered soil and drainage system that allows vegetation to grow on urban rooftops. These living roofs improve the energy efficiency of the building below, promote healthier air and enhance the appearance of urban roofscapes.

Should a PVC membrane be damaged, repairs are relatively simple to do, according to Steve Ruth, director of sales for Duro-Last. “The roofing contractor can heat-seam a patch or fix a curb or a flashing without compromising the roof’s performance,” says Ruth.

When vinyl roofing is damaged by a tear, cut or seam opening, the damage can be spot-repaired. Roofing contractors simply clean and then repair the area with the same methods used to weld the seams during installation.

“But you do want to go back to the contractor who installed your membrane for any modifications so you don’t compromise the roof or your warranty,” says Ruth.

Another advantage of PVC membranes is that they are not weather-sensitive; they can be installed year round. Because of their flexibility and light weight, PVC membranes can be installed in reroof and recover roof construction, over some metal roofs and over built-up roofs, provided the deck is sound.

Technological Innovations
No technology, even a good one, can afford to stand still. PVC membranes are no exception to that rule. Changes to early formulations have led to stronger, more flexible membranes that can withstand the tantrums of Mother Nature.

“The big difference between earlier PVC roofs and those produced today is that all major manufacturers produce reinforced membranes,” says Burkett of GenFlex.

Some early PVCs were not reinforced, and the compounds were designed for European applications where the weather tends to be less severe. When confronted with the harsher climate of North America, some of these early PVC membranes shattered. Improvements and modifications were made in the formulations so that today's PVC roofing is better prepared to deal with what the weather dishes out.

Another technological advance in PVC roofing was replacing solvents for sealing seams with hot-welded seams. No solvent wiping or solvent-based adhesives are required. PVC roofs also can be mechanically attached and adhered with VOC- compliant adhesives.

And, like its TPO counterpart, PVC manufacturers are producing wider sheets. “The wider membranes are more contractor friendly and more financially competitive,” says Brian Whelan, vice president of sales and marketing for Sarnafil.

Details to Consider
Overall performance of PVC roofs has been good. In 1999, Simpson Gumpertz & Heger, Inc., conducted a detailed analysis of vinyl roofing membranes, TPOs and ethylene-propylene (EP). Test data by the engineering firm on 31 different performance criteria, using ASTM D-4434 on 13 membrane samples, were collected and assigned performance values on a scale of one to 100 so the different materials could be compared.

ASTM D-4434 is the only national standard for vinyl-based roofing membranes. It sets a minimum 5,000 hour requirement for weathering performance, based on an accelerated weathering test subjecting the material to simulations of sunlight, water spray and elevated temperatures. To pass the test, the membrane cannot have any cracking or crazing, and discoloration must be negligible.

When averaged, the performance ratings of seven of the eight vinyl samples in the analysis outperformed the other materials, 36 percent better than TPO samples and up to 57 percent better than EP.

The most important PVC membrane difference is thickness, says Bob Cujé of Johns-Manville. “PVC is commonly sold in 50, 60 or 80 mil thicknesses,” says Cujé. “Facility managers should consider ‘good, better and best’ when evaluating their needs. For example, General Motors uses 80 mil almost exclusively, as their building investments are generally modeled on a 20-year plant life cycle. Developers, on the other hand, may have quality in mind, but are generally not holding their properties for the long haul.”

A 1996 study by Simpson Gumpertz & Heger, Inc., places the average lifespan at 14 years for both reinforced and unreinforced systems. According to General Roofing Company, 14 years is the average lifespan of commercial roofing, regardless of type, so properly installed PVC membranes compare favorably with other roofing options.

Like other roofing options, PVC is not for every roof. According to SPRI, PVC membranes are chemically incompatible with bituminous materials. Early formulations also had problems with the plasticizer leaching to stones used for ballast, according to Gallivan of Stevens. “New formulations correct this by using a polymer that does not migrate and that is blended into the molecular structure,” says Gallivan.

Though PVC roofing membranes offer good performance, they can have problems. For instance, a fierce hailstorm in mid-June punched holes and cracks in the flat roofs at Denver International Airport (DIA). The six-year-old roofs, covering more than 4 million square feet, are being replaced. Insurance will cover some of the damage, and DIA hopes that the airport or its insurance carrier may get additional payments from the roofing manufacturer, as the roofs carried a 10-year warranty.

Facility executives can take steps to avoid problems. Many of these are the same sorts of steps that apply to any roofing selection process. For example, it’s important to specify the appropriate thickness for the membrane, taking into account the potential for severe weather. It’s also important to take a close look at the manufacturer and contractor.

“Look at the manufacturer’s reputation,” suggests Burkett. “How long have they been offering the product, and are their roofing contractors fully versed in commercial roofing? Make sure you trust the roofing contractor as well. A bad contractor can make the best product fail.”

Gallivan agrees that knowing both the manufacturer and the roofing contractor are equally important. “Look for references on similar building types and projects,” he recommends. “Find out from the contractor how long they have been installing PVC, how much they’ve installed and what their service record is.”

“The best thing to do is to deal with companies that show a dedication to the roofing industry and have been around for awhile,” suggests Oliveira. “Facility executives should be shown documentation that the PVC actually has performed. If you are concerned, let the building tell you what it needs. Sometimes that means bumping up the gauge a bit. Maybe instead of mechanically fastened, the building’s roof would be better fully adhered.” Matching facility needs with system design is a familiar rule, but one that rewards the time spent up front with better long term performance and lower life cycle costs.

Rita Tatum has covered facility management and technology issues for more than 25 years.

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