Simple and affordable vegetative roof systems offer a myriad of benefits to the property owner. (Photo courtesy of GAF Materials Corporation.)
For most architects, the concept of sustainability is nothing new. Up until recently, the designer was the only member of the building team who understood the general concept and interpreted its guidelines on a job-by-job basis. For property owners and contractors, construction costs - and, hopefully - long-term performance, remain the primary drivers.
Today, regulatory agencies and codes at all levels often require architects to follow a rigid set of sustainability standards. Ironically, many of the officials who promulgate these criteria have little understanding, or tend to ignore, energy efficiency requirements from a building envelope perspective.
Admittedly, these issues are complex and involve interrelationships misunderstood by all but the most experienced design professionals.
At this stage of the game, most specifiers responsible for roofing and waterproofing are already familiar with the potential benefits of vegetative roofs and plaza decks, reflective membranes, solar, and other sustainable technologies. The literature on these subjects is voluminous, and a detailed description of each would require many separate articles. The concept of sustainability, however, often remains elusive.
Some reflective single-ply membranes feature a factory-applied coating to limit dirt pickup and maintain energy savings. (Photo courtesy of IB Roof Systems.)
Defining Sustainability
Seven years ago, an international joint committee of recognized experts and roofing specialists gathered information from different countries about the current criteria used for the design, construction and maintenance of membrane roofs that minimize harm to the environment.In a single page document, the committee summarized the key points of roofing sustainability and best practice for designers, property owners, contractors and manufacturers. These tenets include:
1. Minimizing the burden on the environment by responsible use of materials.
2. Conserving energy by improving thermal efficiency of roofs.
3. Extending roof life span by improving long-term performance. (For full attribution and a copy of the report, please visit www.rilem.net/repDetails.php?rep=rep026.)
The task group also agreed with the following definition of a sustainable roof: “A roofing system that is designed, constructed, maintained, rehabilitated and demolished with an emphasis throughout its life cycle on using natural resources efficiently and preserving the global environment.”
According to this definition, sustainable development requires that roof construction methods, their relationship with the environment, life cycle analysis and environmental quality all work in harmony.
The committee’s third tenet (extending roof life span) and the above definition share one thing: It is all about taking a long-term approach.
Unfortunately, this is where many of the current and proposed codes and standards on sustainable roofing and energy efficiency fall apart.
Properly designed and installed, photovoltaic solar technology gives property owners a virtual power plant up on the roof. (Photo courtesy of GAF Materials Corporation.)
The Cost of Sustainable Roofing
From a building envelope perspective, the benefits of designing a sustainable or “green” building often far outweigh the additional construction costs.Consider the Terrazzo, an under-construction, multi-family, mixed-use urban development located in The Gulch - Nashville, Tennessee’s $400 million Arts Redevelopment District. When it comes to sustainability, the architects and developers of The Gulch’s current crown jewel seem to have done everything right.
The 300,000-square-foot, $68 million, 14-story structure is the first mixed use/residential high rise in the Southeast to achieve Silver LEED (Leadership in Energy Efficiency and Design) pre-certification from the U.S. Green Building Council. When construction is complete and final certification achieved, Terrazzo will also be the first LEED-certified high rise in Nashville.
Bill Barkley is president of Crosland’s Tennessee division - the developer for Nashville’s Terrazzo and master planner for The Gulch. He estimates that green building initiatives add 1 percent to the cost of his project. That figure equates to about $700,000 - not pocket change, to be sure.
“However, on a high-end project like this, we probably would have met most of the LEED requirements anyway,” he reasons.
In addition to relatively exotic mechanical systems, Terrazzo features a long list of green initiatives, including vegetative rooftop terraces and a reflective and well-insulated low-slope roof.
“Many lenders are beginning to require LEED certification for Class ‘A’ buildings and the major pension funds are stressing it,” says Barkley. “Besides, we wanted to build a 21st century building that is not going to become obsolete in a few years.”
The developer hired Greenshape, a Washington, D.C.-based green building consultant, to help with material selection, design techniques and process guidance.
“Besides the obvious energy savings and environmental benefits, achieving LEED certification is like the Good Housekeeping Seal of Approval,” says Barkley. “It demonstrates to our tenants that we went through a rigorous process and did what we said we would do.”
Architect Manuel Zeitlin, AIA, LEED AP and principal of Manuel Zeitlin Architects, Nashville, takes the importance of LEED certification a step further: “First, we don’t have a choice anymore - the clock is running out on renewable resources. Second, LEED certification recognizes that the building is designed to be environmentally sensitive.”
“It’s amazing what a 1 percent investment in front-end costs will achieve in savings on operating and life-cycle costs, as well as providing a healthier environment for occupants that helps to attract and retain tenants and their employees. And that doesn’t even reflect the unexpected exposure that the project has received,” adds co-architect David Bailey, AIA, LEED AP, of Hastings Architecture Associates, LLC, Nashville.
However, this scenario is relatively rare in the commodity construction market, especially when it comes to roofing. A vegetative roof is at least four times the installed cost of a typical $7 per-square-foot system. More important, sustainability requires good roofing practice, which is sometimes absent on “green” roofing projects.
“The biggest challenge I personally see at present is the rapid growth of green roofing that includes all manner of issues - recycling, vegetated rooftops, solar, reflectivity, and others too numerous to list,” says David R. Hawn, RRC, CEM and president of Dedicated Roof and Hydro-Solutions LLC, Centreville, Va.
Like most architects, roof consultants like Hawn have no agenda, barring the provision of a good roof for the building owner. That these comments also come from The Institute of Roofing, Waterproofing, and Building Envelope Professionals (RCI’s) first vice president make them even more credible.
“There is an opportunity to increase roofing risk and make mistakes as a particular green aspect that affects the way we roof buildings is pursued,” Hawn says. “Some of these are even promoted with incentives before we truly understand the influence these concepts have on roof performance.”
For example, when it comes to true sustainability, the EPA’s Energy Star program is sorely lacking.
“Just throw ‘white’ on it, and it’s great,” says Tom Hutchinson, AIA, FRCI, RRC and principal of Hutchinson Design Group Ltd. in Barrington, Ill. “There are so many outside influences with no vested interest telling the roofing industry what to do, with no liability on their part.”
Because the Energy Star program does not take a “systems” approach and only considers roof membrane reflectivity, actual energy savings can vary greatly from project to project.
Consider the 1 million-square-foot, Energy Star-rated, reflective roof membrane inspected last winter by Hutchinson in the Upper Midwest. The roof consultant estimates that the roof system cost the property owner 14 percent of his expected annual energy savings before the installers even left the roof.
There was nothing wrong with the reflective single-ply membrane. However, it was mechanically fastened to a steel deck through a single three-inch layer of insulation. Every fastener became a thermal short, with condensation forming a half-inch thick layer of ice under the membrane.
Where was the vapor retarder and/or second layer of staggered polyiso? Certainly, a fully adhered system using a cover board would have helped.
At this writing, even the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) have prepared an early draft document on sustainability which mentions nothing about using two layers of insulation.
Roofing consultants are also concerned about long-term (three-year-plus) dirt buildup on some reflective membranes and exactly what to do about it.
On the garden roof side, the International Code Council (ICC) says all vegetative roof systems must undergo wind and fire testing, but standards development in these areas is only just beginning.
The increasing number of electrical contractors who are taking over roof responsibilities on solar jobs and subbing out roofing work is another concern in the contracting industry. Sustainability and green building are the biggest roofing trends since the advent of single-ply membranes in the late 1970s. As in that industry, a combination of time-proven materials, roof designs and application techniques will be required to avoid an ugly shake-out for sustainable roof systems.
