TPO on Top
By Loren Snyder - November 2002 - Roofing
Roofing systems typically receive attention only when they require maintenance. As long as a roof needs minimal maintenance and keeps the contents of a facility dry and safe, maintenance and engineering managers have little think about —or so the reasoning goes.
But roofing manufacturers say there is quite a bit to consider, especially when considering single-ply systems. According to manufacturers, these systems continue to garner interest, thanks in part to the cost and performance benefits they deliver.
Although varieties of single-plies have been around for more than 40 years, only in the last decade has the full performance potential of the systems been realized with the advent of new thermoplastic formulations. New plies also are increasingly economical, say manufacturers, and particularly favored by consumers when they carry Energy Star ratings.
Single-plies exist predominantly as two types: vulcanized unweldable elastomerics — nearly all of which are based on an ethylene propylene diene monomer (EPDM) rubber — and weldable thermoplastics such as polyvinyl chlorides (PVC) and thermoplastic polyolefins (TPO).
EPDM remains a popular roofing choice because of its durability and economy, manufacturers say. Usually ballasted or adhered, EPDM systems have a proven performance record after several decades of use.
PVC has also been around for several decades; because of the formulation of PVC, many roofing manufacturers recommend it for installations that require chemical-impervious roofing.
TPO is the fastest-growing category of single-ply systems. Manufacturers say its market share is beginning to grow because TPO costs are coming down and because of the numerous benefits of using the material.
“There’s significant push for TPO systems because of its environmentally friendly nature, because it’s a recyclable product, and because of its energy-saving characteristics,” says Mike McAuley, national sales and marketing manager for Versico Inc.
But TPO systems are newer products that do not have the performance history of some single-plies. Some manufacturers also say that TPO formulations continue to be tweaked to improve longevity and weathering.
“Ultimately, TPO formulation remains a balancing act between fire retardants in the formula and the stability of UV-light protection elements in the formula,” says Brian Whelan, vice president of sales and marketing for Sarnafil.
McAuley agrees, adding that most, if not all, TPO systems remain in an “incremental improvement stage.” Manufacturers have established durable base formulations but introduce small changes to improve certain qualities, including fire resistance.
TPO first was used more than 20 years ago to sheathe buried cable and protect other sub-grade materials.
McAuley says specifiers in institutional and commercial facilities are learning about TPO performance and more often choosing it over other single-plies because costs are coming down. He says TPO material costs are higher than those for EPDM, but installation labor costs are lower.
Sarnafil’s Whelan says another reason specifiers favor TPO is because uncolored versions frequently carry an Energy Star rating. To meet Energy Star
“Increasing numbers of property owners seek the benefits of reflective roofing,” says John Gardner, low-slope roofing marketing manager for GAF Materials Corp. “You get the potential of energy savings, with distinct environmental benefits and the good public relations opportunities that also come with it.”
By reflecting solar energy, reflective roofing lessens summertime cooling loads, saving facilities money. Because Energy Star roofing by definition has high emissivity — giving off heat, rather than holding it — it also reduces the urban heat island effect, Whelan says.
Keeping it Clean
Over time, however, roofing materials accumulate dirt or grow mold, lessening roof reflectivity. To continue reaping the benefits of reflective roofing, managers should clean the roof, using a power washer, a minimum of once annually.
Mold is a sensitive topic for roofing suppliers and maintenance managers alike, one manufacturer says. Some companies, including Stevens, use fungicides or algaecides in TPO formulations to combat mold growth. But these biocides do not always prevent the buildup of mold and mildew, and some might lose effectiveness over time.
Other mold-eradication options exist, especially for the Southeast United States, where geography and weather conditions tend to support mold growth.
“Mold grows on all kinds of roofing materials, not just single-ply,” says Sarnafil’s Whelan. “We’ve discovered that water passed over zinc kills fungal growth. For sloped roofs, Sarnafil is investigating incorporating zinc ridge strips so that a natural rainwater wash kills roof molds.”
GAF makes a family of membranes designed to fight molds, and the company is establishing a mold resource page on its Web site to give managers information on strategies to fight mold. Regardless of the methods used to prevent mold build-up, manufacturers stress the need to wash roofing regularly.
“The only way to keep a roof clean and truly, effectively get rid of mildew is to spray the roof,” McAuley says.
Also vital to the health of single-ply roofing systems are regular inspections of the membrane. Manufacturers encourage maintenance managers to schedule roofing inspections at least yearly, to clear debris and check seams, flashing joints and vent boots for signs of damage. If protective coatings are used, managers also should have inspectors check and repair those as needed.
Gardner recommends managers keep a roof log and offers the following tips to keep single-ply roofing in top shape: criteria, low-slope roof materials must have an initial solar reflectance greater than 65 percent. After three years in place, reflectivity must remain greater than 50 percent.
- Maintain a roof maintenance file, keeping a log of repairs or service done to the roof, as well as other work not directly related to the roof, such chiller maintenance, that requires rooftop traffic. The log should include inspection dates, with notes of any findings.
- Inspect roofs twice yearly.
- Inspect roofs after severe weather. Severe weather, including hail and strong winds, can damage roofing.
- Promptly remove debris from roof.
- Minimize rooftop traffic.
“Most damage to roofing occurs during construction, particularly if other trades use the roof as a staging area,” Whelan says.
Gardner agrees that workers are often a common cause of membrane punctures.
“Minimizing the number of people and the need for them to be on the roof helps maximize membrane integrity,” he says.
Until several years ago, U.S. manufacturers crafted TPO membranes in thicknesses of 45-60mm. Meanwhile, European manufacturers were creating thicker membranes. But that has changed. Now, U.S. manufacturers have bulked up their ply thicknesses, making membranes up to 80mm thick.
“I’m seeing more customers requesting thicker membranes, switching, say, from 48mm to 60mm membranes,” Whelan says. “Generally, there’s no difference in labor costs for different thicknesses. The only cost difference is in the material itself, and those costs usually aren’t that significant. Remember that thicker materials are less likely to puncture, will last longer and carry longer factory warranties.”
That is why Whelan also recommends that when bidding out jobs, managers should ask for bids on at least three membrane thicknesses. Many specifiers also are increasingly choosing mechanically fastened membranes over adhered or ballasted.
“It can be difficult and frustrating to find leaks on ballasted roofing because it requires contractors to move aside massive amounts of aggregate,” Whelan says.
Manufacturers also say that mechanically fastened systems are stronger and require less installation time than adhered or ballasted systems. Tom Gallivan, marketing manager for Stevens Roofing Systems, says mechanically fastened systems use few, if any, adhesive solvents, a consideration for managers who want to maximize environmental responsibility.
Although PVC and EPDM remain appropriate choices in some environments, TPO has emerged as a growing player in the single-ply roofing market. The material’s combination of strength, energy-efficiency returns and economy makes it an increasingly appealing option for managers.
Despite these benefits, managers need to invest the time to conduct regular rooftop inspections, minimize roof traffic, and — when using an Energy Star roof — wash the membrane to help it retain its efficiency.