Roofing Strategies Reach New Heights: Sustainable Options for a Key Building Element  

Offering far more than mere protection from the elements, a roof can define a building's aesthetics, and add beauty, drama and distinction to the look and feel of any project. Today's roofs can also be sustainable building elements in their own right, upping the green quotient of the structure they cover.

 Sustainable roofs share several characteristics: some are built with materials created with minimal energy consumption and that have no negative impact on the environment. They require limited maintenance, are easily repaired and generate limited waste throughout their life cycle - and they're designed for long-term performance and extended life spans. These key goals are even more vital in light of current statistics. The U.S. Department of Energy (DOE) estimates that over a building's lifetime, some roofs need to be replaced an average of four times. Nearly three quarters of the roofing work done in the United States, in fact, is re-roofing, with old roofs pegged as the second largest contributor to solid waste generation, as well as being the second most prevalent castoff found in the nation's landfills. According to the Oak Ridge National Laboratory, most of this waste is from asphalt built-up roofing and modified-bitumen roofs removed prior to re-roofing - though tons of waste is generated by other types of roofing systems during both installation and tear-off.

Sustainable roofs also conserve energy through the thermal efficacy of materials used - an area which has received considerable attention. Just as dark clothes make you warmer, dark surfaces in the sun can become up to 70 degrees Fahrenheit hotter than the most reflective white surfaces. Dark roofs can also transfer some of that heat inside the building, boosting air-conditioning demand and energy bills. What's more, dark roofs jack up the temperature around them, adding to the heat island effect.

A natural tile roof is an aesthetic and sustainable choice. Photo courtesy David Ricketts at FX Imaging Inc.

 

The solution is a cool roof - defined by the Cool Roof Rating Council (CRRC) as one that "reflects and emits the sun's heat back to the sky instead of transferring it to the building below." A growing list of states and cities are already mandating cool roofs. "What's driving the change in roofing systems is cool roof legislation, but also a growing concern for the environment and a sustainability awareness that didn't exist twenty years ago," says Nick Causey, executive vice president for Quest Construction Products and former president of Hydro-Stop, noting that architects and users alike are increasingly interested in roof systems that last longer and promote green goals. "A roof is one of the most important building elements in terms of sustainability," says Rich Thomas of the US Tile Company. With so much at stake, it behooves architects to make the right choice for a particular project. This article will discuss roof systems, roof flashings and curbs and new sustainable roofing products that represent sustainable options for today's buildings.

A fluid-applied roof can be both waterproof and beautiful as in the example at the Waikiki Beach Walk Outrigger Hotel in Honolulu. Photo courtesy of Hydro-Stop/Quest Construction Products

Clay Tiles for Steep Slopes

Clay is one of the oldest roofing materials in existence, with clay tiles dating back as far as 3,000 B.C. in ancient civilizations in China and the Middle East. Clay's staying power stems from the fact that it is fire resistant, non-combustible, low maintenance, will not rot, and can stand up to strong winds, temperature changes, and freezing and thawing. Clay tiles made of naturally occurring materials will not fade over time. "They're 99 percent dirt and water," says US. Tile's Thomas, noting that natural clay tiles are 100 percent recyclable, and can contain as much as 59 percent recycled materials. Because it contains complex inorganic color pigments that boost its reflectance in the infrared spectrum, clay is said to have a natural reflectivity.

In this "cool roof" blend, all clay tiles have an SRI value of greater than 29. Photo courtesy of US Tile

The color in natural clay tiles is determined by the natural occurrence of trace elements such as iron, chrome and nickel, as well as by the kiln temperature, and oxygen present during the firing process. Alternatively, tiles can be coated during manufacturing, a somewhat easier and less expensive option than obtaining different clay sources to produce specific colors, the tradeoffs being authenticity and susceptibility to fading. Firing can be energy intensive, though natural clay tiles can utilize a quick fire method using a roller hearth kiln that cures the tiles in 60 to 110 minutes, lowering firing times and saving energy. Other manufacturers, particularly those that glaze tiles, use other types of kilns that can take up to one week to fire products. Over the past decade, the industry has been able to reduce energy usage significantly - some manufacturers claiming up to 27 percent - by continually upgrading equipment and process and utilizing alternative energy sources, such as solar energy or purchasing certificates for renewable energy off the grid.

Clay roofs can be used in any climate, and have a wide range  applications on residences, small and large businesses, and academic buildings. Properly maintained clay roofs - either natural or coated - have life expectancies of 100 years or more. "The main reason for most roofing products' degradation is water absorption," says Thomas. "Products with the best longevity are typically those with low water absorption rates." To gain that property, all clay tiles, like bricks, are vitrified, meaning they are kiln fired to 2000 degrees Fahrenheit to achieve the density that will lock out water absorption. Very fine particle size also helps eliminate voids in the body of clay tile that limit water absorption even further. Clay tiles so fired are appropriate for any climate condition including salt intrusion experienced in coastal areas, severe freeze thaw action, and snow loads of harsh climates.

Depending on their color, natural reflectivity and glaze, some of today's clay tiles are rated "cool" by the Cool Roof Rating Council. A cool rated roof differs from a non-rated roof in two aspects: it reflects the sun better and dissipates heat more effectively. To measure reflectivity, a machine is used to take readings on six different random areas of an installed tile, with reflectivity based on an average of the readings. Emissivity is measured by a specialized emissometer machine that measures the amount of heat that travels through the product. Clay can reflect 53 percent of the sun's energy - vs. 10 percent for asphalt shingles - and emits 86 percent of the heat, allowing the roof surface to stay relatively cool compared to the ambient temperature. That, in turn, minimizes the heat island effect and interior heat fluctuations at the top of the building next to the roof. Clay has been shown to deliver up to 36 percent less ceiling heat fluctuation than concrete tile, and 75 percent less than asphalt shingles, reducing dramatic swings in ceiling temperatures, which saves energy and reduces the strain on building cooling systems, especially during peak expensive rate periods.

Source: Oakridge National Laboratory

 

A cool roof doesn'thave to be a white roof. Even darker colored clay tiles can have an innate reflectivity that eliminates the need for paints or additives to reach an SRI (Solar Reflectivity Index) rating of 29 or greater, the magic number for LEED compliance on steep slope roofs. "Because of this natural reflectivity, clay colors that meet the LEED cool roof requirements are typically going to have darker and richer colors than other products such as concrete or asphalt," says Thomas.

In specifying clay tiles, architects will want to examine the manufacturers' warranties to be sure that they cover fading for at least 20 years. Another point to look for is Cradle to Cradle certification granted by MBDC (McDonough Braungart Design Chemistry), a consultancy founded in 1995 by architect William McDonough and chemist Michael Braungart to reorient the design of products, processes and systems to provide financial, environmental and societal benefits. C2C provides manufacturers with a means to measure achievement in environmentally intelligent design and helps customers purchase and specify products that are pursuing a broader definition of quality. Within the terms of the C2C program, this means using environmentally safe and healthy materials design for material reutilization, such as recycling or composting energy efficiency and the use of renewable energy efficient use of water, and maximum water quality associated with production; and instituting strategies for social responsibility. If a candidate product achieves the necessary criteria, it is certified as a Silver, Gold or Platinum product and can be labeled as Cradle to Cradle. In April 2007, the U.S. Green Building Council established an innovation point for specification of products certified under the Cradle to CradleSM (C2C) Certification program. "C2C is another opportunity for clay tiles to earn LEED points," says Thomas. "Clay tile roofs have the potential to help in seven or eight LEED categories, whereas other roofing systems may be able to help in two to three."

The extra LEED point for Cradle to Cradle certification helped push the 39,000-square-foot athletic building on the Santa Margarita Catholic High School campus in Rancho Santa Margarita, California, closer to LEED silver certification. Architect Jon Gomer LEED AP of tBP/Architecture in Newport Beach specified a "cool" clay tile roof to match surrounding buildings. "We chose a through-color tile rather than one with a painted-on surface because it would last throughout the building's life cycle," says Gomer. "That it was also a ‘cool' roof product made it the right choice to pursue LEED credit points. And as an added bonus, the Cradle to Cradle certification qualifies the building for an additional Innovation Design point - and that's a plus you don't currently find with other clay tile."

The Westminster, California, Chamber of Commerce building features a barrel tile roof that contributes to LEED Gold certification. Image courtesy of Dougherty + Dougherty Architects LLC

 

 In its new Chamber of Commerce Building, the City of Westminster, California, sought to set a standard for contextual and sustainable design as a community-wide goal, and targeted LEED Gold certification from the outset. An integral part of the strategy was a sustainable roof. Dougherty + Dougherty Architects LLP of Costa Mesa specified a clay tile roof with the barrel profile and variegated texture prevalent in the community and consistent with city's traditional design preferences. "The roof was self venting, exceeded LEED SRI criteria and was cost competitive, which is where the rubber meets the road," says Dougherty + Dougherty Partner-in-Charge Betsey Olenick Dougherty, FAIA, LEED AP. "To achieve a green advantage with what is considered to be a traditional material is truly a breakthrough." The project is in construction, with LEED criteria embedded into the specifications. "Architects are in an extremely powerful position to implement a green agenda," Dougherty adds.

Clay Goes Solar
The newest innovation in clay tile roofing is a recently launched building-integrated photovoltaic roofing product (BIPV) that uses flexible thin film solar cells. The thin film laminate is bonded to the polymer tile with a proprietary adhesive material and process to produce the first curved solar tile to be introduced to the U.S. marketplace. They look like standard Mission clay tile and are light weight and easy to install. The thin film solar tiles are currently available in a "solar blue," barrel-shaped profile that mesh seamlessly with blue-glazed tiles of a similar profile, or in a profile-only integration with clay tile of earthen hues. They have been tested under harsh conditions for durability, including UV stability, color fastness, wind resistance, electrical output, safety, and extreme mechanical stresses. UL and ICC code approvals are anticipated this fall. "It's a quantum step for solar energy," says Thomas. "The question has always been: how do you incorporate a solar cell without sacrificing curb appeal."  

While solar systems are typically installed by the watt, energy is generated and billed by the kilowatt hour (kWh). The value of a solar system then, or its rate of return, is dependent on how many kilowatt-hours it generates, offsetting electrical consumption. In order to determine how much energy the solar system will generate the following must be considered: solar capacity of the system, peak sun hours, system efficiency, and time. Based on these considerations, over a year period, the thin film technology allows the tile system to produce an estimated 10 to 15 percent more energy than silicon panels. "This thin film technology is comprised of three layers of semi-conductor material," says Abby Nessa Feinstein of SRS Energy in Philadelphia, noting that each layer absorbs a different spectrum of light, allowing the cells to convert a broader spectrum of light into electricity. "The light spectrum at dusk is different than that the spectrum at 10 o'clock, noon, so and so forth. And the spectrum is different under cloudy conditions. In essence these cells are ‘less picky' than traditional silicon wafers with regards to which light they convert to electricity," Feinstein adds.

With regard to determining the system size, a number of factors come into play, including location, electrical equipment, demand, etc. According to Feinstein, the average American home uses over 10,000 kWh per year. Assuming this and other typical parameters, in California, an estimated 25 percent of the roof covered by these thin film solar panels could reduce the dwelling's energy bill by 75 percent.

Solar tiles integrate with clay tiles for a seamless look. Photos courtesy of SRS Energy

Fluid-Applied Systems for Flat Roofs

On the opposite side of the roofing spectrum are fluid-applied roof systems. Rather than roof-applied tile-by-tile or shingle-by-shingle systems, fluid-applied roofing is a monolithic system used mostly in commercial settings. Primarily a flat or low-slope roofing solution, these systems are water-based elastomeric acrylic membranes reinforced with a non-woven polyester fabric. A base coat is applied and reinforced by the fabric and subsequent layers of coating. "It all cures as one monolithic system and forms its own flashings," says Quest Construction Products' Causey. Some manufacturers claim their fluid-applied systems waterproof all surface areas associated with the building's roof substrate including the interior and exterior parapet walls and caps, scuppers, drain bowls, through-roof protrusions and decks - and that when properly installed and maintained, fluid-applied systems can remain 100 percent waterproof regardless of weather conditions or age, with virtually no leak points. Roofing systems thus qualified can be covered by up to 20-year warranties on most roofing applications, which can be extended at the conclusion of the warranty period for additional 10-year periods under a prescribed maintenance schedule. In contrast, traditional roofing systems require leak-prone accessories such as sealants, tapes, adhesives, clamps, termination bars, drain rings or counter-flashings. In some cases, manufacturers of traditional roofing systems write exclusions into their warranties because they can't guarantee 100 percent waterproofing capabilities and cannot completely waterproof all areas above the roof substrate - a situation that architects should fully examine in selecting roofing options. "Other roofing manufacturers tend to warrant only their roofing product itself, as flashing is required and they do not manufacture those parts," says Causey, noting that with fluid-applied systems, the flashingis the product. The flashing is covered under the warranty, in all climates and conditions, provided the product is applied according to the manufacturer's specifications by an approved applicator and the proper inspections have been made before, during, and after the installation. Manufacturers may be able to supply years of successful applications as research data.

Manufacturers offer two types of fluid-applied roof systems:

• Reinforced 45 mil acrylic elastomeric systems generally consist of multiple layers of coatings that are reinforced with non-woven polyester fabrics. These systems may be installed directly to the existing roof, eliminating disposal and landfill costs. They are UV- and IR-resistant, have very low emission of volatile organic compounds and nontoxic formulations. System life may be extended with additional coatings every decade, and generally come with 10-year renewable warranties. If a new furnace or AC unit is installed, the designer should require the approved applicator and technical representative to inspect the job, applying new roofing materials to flash any new penetrations.
• Reinforced 50 mil acrylic elastomeric systems with fluoropolymer coatings are installed exactly like a typical 45 mil acrylic elastomeric system but have additional coatings that use state of the art fluoropolymer resins. A fluoropolymer is the next generation of resins - with great weathering and color retention properties. When paired with a fluid-applied roofing and waterproofing system, a flurorpolymer can extend the life of the sustainable roof, extending the time between recoats. The fluoropolymer coatings provide the same advantages of a typical fluid applied system and offer solar reflectivity ratings of 87 percent and higher, well above the SRI LEED compliance number for low slope roofs. "There are several colors that are rated by the Cool Roof Rating Council," says Causey. "White, however, is most often cited for its highly reflective properties. "Cool" colors also do exist, usually in the greys and tans. "The roof coatings also provide higher dirt pick-up resistance, improved color retention, reduced weathering rates - all with 20-year renewable warranties."

A fluid-applied roofing system was used at a resort at Kiawah Island, South Carolina. Photo courtesy of Hydro-Stop/Quest Construction Products

 

A measurable amount of surface thickness is lost over the life of the product and can be replaced by additional coatings. Due to its chemistry, the regenerated fluid-applied roof is as strong as the original installation and will last for another set time period depending on the additional coating's mileage. "Unlike traditional roofing, fluid-applied roofs weather from the top down. So the top of the roof can be cleaned and refinished over and over again, without having to tear out the entire roof system," says Causey, noting that because 95 percent of roof substrates can be coated without requiring any tear off, fluid-applied roofs help to reduce landfill overload. To guarantee adherence, a clean, sound substrate is recommended. Most roof surfaces can be cleaned with water or water and a mild detergent. Since it is a waterborne product, specifications recommend applying the product in weather 40 °F and above.

Architects should make sure that a fluid applied roof system has an FM (Factory Mutual) 4470 approval as a stand alone roofing assembly. Currently there are two test methods being used for approval testing of mechanically attached roof systems, the FM 4470 and the Underwriters Laboratory (UL) 580 procedures. FM approval means that the product has been tested for a variety of parameters including interior and exterior fire exposure, wind uplift resistance, accelerated weathering, hail damage resistance, leakage resistance, foot traffic tolerance, and have passed third party formulations audits and third party production facility audits. In contrast, roof coatings - as opposed to roofing systems - are only tested for exterior fire exposure, and third party audits are not performed. Chad Roberson, AIA, LEED AP, of PBC+L Architecture in Asheville, NC, has used fluid-applied roofs in many applications, with considerable savings to clients. "They're easy to install, and you can patch the surface and it doesn't appear patched," he says, adding, "They're available in literally any color, almost like paint products."

A fluid-applied roof was used at the Tomball Independent School District in Tomball, Texas, to re-roof its Junior High and High School on a very limited budget. The district realized over $25,000 in savings with a reduction of 287,000 kWh one month after installation. The system subsequently stood up to Hurricane Ike with sustained winds of 90 mph and gusts up to 144 mph. Unlike many districts, Tomball did not have to pay for roof repairs as a result of the storm. "These roofing systems have made it through storms like Typhoon Paka with 241 mph wind gusts and Hurricane Wilma with 120 mph wind gusts," says Causey. "Because they're fully adhered and seamless, they can achieve high wind uplift ratings." 

Classified as "cool" by the Cool Roof Rating Council, fluid-applied roofs can have solar reflectance as high as of .79, and a thermal emittance of .90. Fluid applied systems that utilize a Cool Roof Rating Council-approved top coating will further reduce the surface temperature as well as the internal temperature of a building. Any reduction of roof temperature will prolong the lifespan of not only the fluid applied system, but any pre-existing roofs and insulations as well. Cool roof rated fluid applied systems will also benefit roof mounted HVAC units as cooler air will be used in the heat exchange, which makes the units more efficient, and prolongs equipment life.

As opposed to asphalt-based products that must be heated during manufacturing and installation, fluid applied systems don't require heating. Most are waterborne, do not use heavy solvents as carriers, and are manufactured without any harmful by-products such as chlorine commonly out-gassed by various roof systems.

A fluid-applied roof helped reduce energy costs at the Tomball Independent School District in Texas. Photo courtesy of Hydro-Stop/Quest Construction Products

 

Polyurethane Foam and Topcoats: Protecting the Roof

Another sustainable, water-based, roofing system is a topcoated spray-applied polyurethane foam (SPF) system. Dating from the 1960's, SPF roofs are monolithic, fully adhered and self-flashing, that is the polyurethane foam can be used to form its own flashing so no separate flashing materials are required.

SPF conforms to any surface profile to form a tough, waterproof membrane, offering the highest R-Value of any commercially available insulation material. Spray-applied as a two-component liquid, it expands to 30 times its fluid thickness to form a seamless, dimensionally stable blanket over new or existing roof substrates including metal, wood, concrete and built up roofing. "SPF is a good choice when extra insulation is needed, as there is an increase of R 6 to 7 per inch of foam," says Quest Construction Products' Vice President/Business Unit Manager Charlie Van Gelder. He adds that SPF is suitable for use in areas with severe temperatures and/or high winds, as well as for correcting roofs with ponding water problems. "The slope can be built up in to add slope where necessary until the proper drainage is achieved," Van Gelder says, noting that a quality applicator can apply the foam so that it forms a relatively smooth surface, with smooth transitions to details such as flashings and drains. Wind screens can be used to prevent overspray under moderate wind conditions.

Studies have indicated that cured spray polyurethane foam is relatively inert and does not release toxic gases or leach harmful chemicals into the atmosphere or soil. Two separate studies report that the effectiveness of an SPF roof did not diminish over time. A 1996 study for the National Roofing Foundation of 1,600 SPF roofs - with the oldest roofs being more than 30 years old - found that 97.6 percent of the roofs did not leak, 93 percent had less than 1 percent deterioration, and 55 percent required no maintenance.

Topcoating the SPF with an elastomeric coating, typically acrylic, silicone, polyurethane, or aggregate covering, is a must to protect it from UV degradation. Topcoats also work to reduce moisture vapor transmission, increase the roof system's resistance to impact, achieve fire rating code requirements and enhance aesthetics.

SPF roofing systems can be particularly effective, and relatively easy to apply, on roofs of elaborate design or numerous penetrations. The unique roof of the North Shore Congregation Israel in Glencoe, Illinois, built the 1960's, features varying angles and slopes with several rooftop skylights. Upon aging of the original topcoated SPF system, the synagogue opted to replace it with a similar combination of foam and coatings. After the old materials were removed, the building's concrete roof deck was exposed and cleaned, followed by application of the SPF system. Two layers of elastomeric acrylic basecoat were applied over the foam at a rate of 1.5 gallons per 100 square feet each. Two separate coats of a weather resistant fluoropolymer topcoat were then applied at the rate of 1/2-gallon per 100 square feet per coat.

Topcoated SPF was an ideal solution for the roof of the North Shore Congregation Israel, Glencoe, IL. Top images: After shots; Bottom image: During construction. Photos courtesy of Insulated Roofing Contractors of Louisville, KY

 

An SPF system also made sense at the massive MGM Grand Hotel and Casino in Las Vegas, where high temperatures and heavy maintenance had taken a toll on the 214,000-square-foot black EPDM (ethylene propylene diene terpolymer) rubber roof. An SPF roof was installed over the existing substrate and topcoated with a protective acrylic membrane, which provides high-build durability and waterproofing. A reflective fluoropolymer topcoat was added to aid in dirt pick-up resistance and improve durability under foot traffic. Fluoropolymer refers to a type of chemical composition that is a more UV- stable polymer than acrylics or polyurethanes.

A monolithic, spray-applied polyurethane foam roof, topcoated with an acrylic/fluoropolymer for UV protection, durability and solar reflectance, covers the existing substrate at the MGM Grand in Las Vegas. Photo courtesy of the MGM Grand Hotel

 

 "Due to the large amount of equipment and other obstructions, the roof was an ideal application for spray-applied foam and coatings," says Van Gelder. "And most importantly, the fluoropolymer topcoat, with a Solar Reflective Index (SRI) of 110, gives the owner maximum reflectance value for the life of the system."

 

Conclusion

As the quest for green buildings heats up, architects have a key asset in cool roofing strategies. Traditional materials, technological advances, and combinations thereof, offer an increasing array of aesthetic, sustainable options in roofing systems.