Roofing supp jump
August 11, 2010

New Roofing Concepts and Techniques (Continued from p. 61 of the January 2009 issue of BD+C)

                  
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Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. 

 

COOL ROOFS, COOL SAVINGS
Cool roofs can be a more economically viable green alternative to green roofs and BIPVs, says Burt Hill’s Germishuizen. “The technology is understood, risk free, requires less maintenance, and is often easier to sell to clients and end users,” he says. “Installed costs are lower than planted systems, giving building owners options when looking for green or LEED-related products.”

Here’s how they work, according to Aztec’s Funk: “The principle is that if you have a light-colored or reflective roofing surface, the sun’s energy is reflected much more dramatically than a darker color. This means that the roof heats up much less, transmitting less heat energy to the building envelope. This has an impact on [lowering] HVAC demand, which reduces energy consumption.”

In most cases,  cool roofs offer a longer lifespan than their more traditional alternatives. As the cooler systems generally contain the same components as a regular roof, first cost is not significantly different, adds Funk, who has worked with a variety of roofing systems on numerous project types. Cool colors and formulations are available for metal roofs, single-ply membrane, and some built-up roofs using ballast.

One reason cool roofs last longer than traditional roofs is that ultraviolet (UV) rays tend to break down black roof materials faster over time, while cool roof coatings generally slow down this natural process. (Some of the newer single-ply products are made with self-cleaning and mold-resistant polymers to better maintain solar reflectance.) For that reason, cool-roof systems can perform well in preventing leaks, handling greater wind loads, and reducing a building’s internal temperatures, according to Scott Shiver, a contractor with Uniqco Restoration & Coating, Clermont, Fla. “We’ve seen our customers achieve a 15-30% savings on energy almost immediately,” says Shiver. “In Florida, many of these reflective roof restoration systems are earning additional rebates.”

A few terms and technologies related to cool roofs are frequently used by manufacturers and roofing consultants. Among the most pertinent for Building Teams, according to the U.S. Environmental Protection Agency, are two performance measurements and three roofing products in addition to single-ply:
Solar reflectance – Also called albedo, this is the measure of the ability of a surface material’s ability to reflect sunlight—including the visible, infrared, and ultraviolet wavelengths—on a scale of 0 to 1. The higher the rating, the greater the solar reflectance.
Solar emittance – This ranks the ability of a material to release absorbed heat. Emittance is measured between 0 and 1, or 0% and 100%. Again, the higher the rating, the greater the solar emittance.
Cool roof coatings – These typically include white and light-colored paintlike liquids applied with a power sprayer or roller over existing roof structures or claddings. Recent advances include low-odor products and coatings with higher solids content, which can be applied in one coat rather than two.
Cool metal roofing – Unlike untreated metal, which efficiently absorbs and retains heat, cool metal roofing products offer high albedo to better reflect the sun’s radiation, keeping the roof cooler.














      
A 15,000-sf “cool roof” at the Dover Professional Center, Toms River, N.J. (top), uses a branded modified bituminous two-play system with a light-colored aggregate finish to reflect sunlight. Bottom image shows flashing around columns.
         

Cool tile roofing – While traditional clay or concrete tiles usually have a solar reflectance of 10-30%, cool tiles contain pigments that both reflect up to 70% and enable roofing materials to keep their traditional colors, such as brown, green, and terra cotta.  

Ballasted roof systems. Another common approach to creating a sustainable, energy-efficient roof is using a ballasted roofing system. This usually consists of a membrane or built-up roof, such as modified bitumen or asphaltic materials, topped with gravel or stone or concrete pavers. Some planted roofs may be ballasted types; in any event, some Building Teams favor the natural finished look and the added thermal mass of the ballast. Although the ballast material has a relatively low thermal resistance, or R-value, the combination of the stone mass and air spaces act as an effective insulator.

A ballasted system with at least 17 pounds of stone per square foot offers about the same surface reflectivity as a cool-roof membrane system. For that reason, it has nearly the same effect in mitigating peak energy demand, according to a recent study conducted by the Oak Ridge National Laboratory, “Evaluating the Energy Performance of Ballasted Roof Systems”  (http://www.spri.org/pdf/Thermal%20Performance%20of%20Ballast%20Study%20Final%20Report%2005%2008%20.pdf). Based on three years of experimental data, the study also found that some ballasted systems actually performed better than reflective roof systems in reducing the urban heat-island effect. With such compelling findings, the study’s conclusions prompted ASHRAE and the California Energy Commission to update their cool roofing standards to recognize ballasted applications as an acceptable alternative to cool roofing requirements.

Ballasted roof systems also work well as a hybrid in combination with landscaped roofing, which can reduce first costs while simultaneously maintaining solar reflectance and water retention benefits. Additional sustainability benefits include an average service life of 15 to 20 years and the ability to remove and recycle the underlying roof membrane and insulation, which better maintains integrity in the absence of excessive mechanical fasteners and adhesives required by other roofing systems, according to James L. Hoff, research director at the Center for Environmental Innovation in Roofing, Washington, D.C.

AIR AND MOISTURE PROTECTION
Although green roofing innovations like vegetated roofs, BIPV, and cool roofs offer much in the realm of energy efficiency and building performance, a more elementary but critical issue is protecting the roof membrane against air and moisture penetration. “Figuring out where the water wants to go versus where you think it will go is not always a straightforward process,” says Funk. “There are issues that are not so easily managed, like capillary action, condensation, freeze-and-thaw cycles and ice damming.” In general, Funk recommends what he refers to as a “belt-and-suspenders” approach to roofing: Keep things simple, and design so that, if part of the system fails, either due to improper installation or a lack of proper maintenance, the whole system won’t fail.

Whatever design strategy you choose, Funk emphasizes the importance of sealing all openings. “It’s all in the details. Terminations, penetrations, expansion, contraction, and tie-ins are some of the major sources of a roof breach,” he says. “Once the right materials and system are selected, it is essential for the proper details to be followed and the execution performed correctly.” Follow-through by the entire Building Team, from architects and engineers to the general contractor and specialty trades, is essential.

For example, roofing consultants and contractors point out that if water saturates the insulation or gets behind a partially installed roof membrane during installation, there can be major problems: when water evaporates and is trapped behind the roofing layer, the membrane materials can bubble or delaminate.

Barrier materials. With regard to air barriers, the well-known building envelope expert Wagdy Anis, FAIA, a principal with Wiss, Janney, Elstner Associates, Cambridge, Mass., explains that fully adhered or hot/cold-mopped roof membranes can actually serve as air barriers. The National Roofing Contractor’s Association’s Roofing and Waterproofing Manual also states that the roof deck itself can work as an air retarder if it is monolithic, such as cast-in-place concrete: “When the deck is used as an air retarder, deck penetrations such as plumbing vents should be sealed, and the deck should be sealed at parapets,” the manual recommends.

On the other hand, with mechanically fastened or ballasted roof systems, an air barrier must be designed into the system. As Anis explains in his article on this subject in the Whole Building Design Guide, an online green building design resource with content developed by federal agencies and expert private-sector consultants (http://www.wbdg.org/resources/airbarriers.php), “Either a peel-and-stick air-and-vapor barrier on the inboard side of the roof system (interior conditions and weather dependent), or taped gypsum underlayment board beneath the insulation can be used in a system with adhered underlayers of thermal protection board and insulation.”

Because an air barrier system will not work effectively unless it is carefully coordinated, Anis stresses the importance of close collaboration among the trades. “A preconstruction conference on the air barrier system must include the trades involved in the air barrier system, such as the wall air barrier subcontractor, the window subcontractor, the sealant subcontractor, and also the roofing subcontractor, to discuss the connection between the roof air barrier and the wall air barrier, as well as the sequence of making an airtight and flexible connection.”

Germishuizen recommends regularly scheduled job conferences, field inspections, and required interim inspections and testing by the roof system manufacturer during the installation phase, in addition to regular coordination between the owner, architect, and contractor throughout all project phases.

Polyurethane foam. Among the different product types available to effectively seal roofing systems is spray polyurethane foam (SPF). Acting as a vapor, moisture, and air barrier, spray foam can mitigate condensation problems and vapor drive, which can damage roofing materials and other parts of the building envelope, according to Funk. This also reduces the opportunity for mold to develop, as spray foam insulation does not support the growth of mold or mildew, he adds. And because the foam doesn’t settle or shrink over time, it maintains a seal against air leakage, which is a major source of heat loss.

According to Germishuizen, SPF works particularly well with flat roof applications over large areas in urban heat-island zones. “Due to the nature of the spray application, the material can be applied over irregular surfaces and shapes to create a seamless, monolithic membrane surface,” he notes. “The spray-applied, low-rise foam also allows the installer to increase the amount of foam applied to areas where water tends to pond on roof surfaces due to deviations within the structure.”

On the other hand, NBBJ’s Highman favors extruded polyurethane foam panels. In terms of performance, he says that these panels—sloped and flat—provide technical advantages to sprayed products. “When the mechanical engineer does an energy model for the project, his or her bottom line calculations have a higher degree of accuracy, and from the contractor’s point of view, installation of rigid panels is quick, clean and safe, not to mention standard practice,” says Highman.

Other products, such as elastomeric bitumen, which strongly adheres to most construction surfaces, and rubberized elastomeric membrane, which is durable, UV- and weather-resistant, also offer viable solutions based upon the nature of the project. Adhesive sheet products are lightweight, don’t require mechanical fasteners, and offer a variety of options, whether it’s blocking air and water while allowing vapor through so that the assembly can breathe, or self-adhesive membrane bonds that actually strengthen over time.

Funk says he recently specified such a product for a project located next to a school where fumes and off-gassing were a concern. “We chose a self-adhering, two-ply modified bituminous product as there are no VOCs and minimal odor, and it was relatively easy to install,” he says. (“VOCs” refers to volatile organic compounds.)

ROOFING CONSTRUCTION: BEST PRACTICES
New roof installation techniques are helping to achieve the goals of saving costs, improving efficiencies, and even promoting better product performance. “For example, insulation performance is improved when using a double-layer system with staggered joints in lieu of a single-ply system,” says Germishuizen.

According to Highman, construction equipment such as tower cranes and other rapid installation systems can play a key role as well. “Tower cranes can be used to stage materials and assist in material distribution, although they must be scheduled well due to their high [rental]  costs. For the installation of low-cost systems, low-pressure hydro-seed installation equipment offers a huge advantage as the material to be spread is almost liquid and easy to pump, while the equipment is relatively light and usually only one person is required to operate the entire process.”

Some additional installation innovations are delineated by Tom Smith, AIA, TLSmith Consulting Inc., Rockton, Ill., in a section he wrote for the Whole Building Design Guide (at http://www.wbdg.org/design/env_roofing.php):
• Wider single-ply sheets for mechanically attached application, requiring few rows of membrane fasteners and fabricated field seams.
• Non-bituminous adhesives in place of mechanical fasteners to attach insulation.
• Self-adhering, single-ply membranes offer faster installation, are more environmentally friendly, and eliminate the need for adhesives and torches for installation.
• Mechanized rooftop application equipment and heavier ballast spreaders.

Yet another trend is sustainable product development. Roof insulation manufacturers are making breakthroughs in the use of recycled material, such as cellulose fiber, denim, and wool, and post-industrial and post-consumer materials, in the development of products, says Germishuizen. According to Funk, greater attention toward VOCs and recycled or recyclable products is impacting how material is managed and installed on site. 

LIFE CYCLE BENEFITS IN ROOFING
Sustainable elements are also contributing to the life cycle benefits inherent in roofing systems. “Life cycle may be the greatest attribute of a green roof,” suggests Womack. “There are roofs in Germany that are 50 to 60 years old and they have never been replaced, because the roof is protected from UV rays and freeze-thaw cycles—two elements that have the biggest impact on a roof.”

In terms of recycled content and recyclability, metal roofing components likely offer the greatest opportunity for building projects. According to Durhman, however, such materials as ballast, rubber, and PVC can be recycled into other roofing products or reused on rooftops as well.

Some systems have much to offer when taking a larger, whole-building system approach, according to Funk. For example, panelized or modular roofing systems that can accommodate not only the functions of a roof, but also provide insulation and some structural spanning ability, accomplish several functions in one. This can speed up construction and offer greater economy by eliminating the need for separate systems and separate trades. 

“That means less material to manufacture, ship, handle on site, and install,” he says.
As for future offerings, an improved, long-lasting, and recyclable PVC-based waterproof membrane is under development, as well as a biodegradable tray system that breaks down over time, putting nutrients into the soil and eventually providing a monolithic growing medium for the plants, according to Womack.

But while sustainability continues to gain momentum, it still must compete with the problem of higher initial cost—real or perceived.  “As sustainability and cradle-to-cradle practices become more common and have less of a cost increase associated with them, I think more clients will be receptive,” Funk concludes. “Clients like the idea of environmentalism, but in the end it comes down to, ‘What will this cost me?’”

About the authors

C.C. Sullivan is a communications consultant and author specializing in architecture and construction. Barbara Horwitz-Bennett is a writer and contributor to construction industry publications.


























































Take the AIA Exam  (one-time registration required)

This BD+C continuing education program qualifies for 1 AIA HSW learning unit.

Reed Business Information is a Registered Provider with the American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be reported to CES Records for AIA members. Certificates of Completion for non-AIA members are available on request.
       This program is registered with the AIA/CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation.


         
 

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