There Is Evidence Cool Roofs Provide Benefits to Buildings in Climate Zones 4 through 8

FIGURE 1: Reflective roof requirements in ASHRAE 90.1 and IECC only apply in Climate Zones 1 through 3, shown here on the ASHRAE Climate Zone Map. SOURCE: U.S. Department of Energy

FIGURE 1: Reflective roof requirements in ASHRAE 90.1 and IECC only apply in Climate Zones 1 through 3, shown here on the ASHRAE Climate Zone Map. SOURCE: U.S. Department of Energy

Reflective roofs are a tried and true way to improve building energy efficiency and comfort, generate net energy savings and help mitigate summer urban heat islands. Reflective roofs work by reflecting solar energy off the roof surface, rather than absorbing the energy as heat that can be transmitted into the building and surrounding community.

The simple act of switching from a dark to a light-colored roof surface has a number of benefits. Buildings protected by these types of roofs require less energy to cool and help building owners and residents save money. Cool roofs on buildings without air conditioning can save lives during heat waves by lowering indoor temperatures. Cooler city air is safer to breathe and less polluted, which makes cities more livable and less vulnerable during heat waves. Increasing the reflectivity of urban surfaces can also offset the warming effect of green- house gases already in the atmosphere and help us address the challenges of climate change. Taken together, these benefits are worth billions of dollars to the growing number of people that live and work in U.S. cities.

The energy-savings case for cool roofs in warm climates is clear. Widely adopted model building-code systems, ASHRAE and the IECC, address roof reflectivity. ASHRAE 90.1-1999 added a credit for highly reflective roofs with IECC allowing compliance via ASHRAE in 2003. ASHRAE 90.1-2010 added reflectivity requirements for new and replacement commercial roofs in Climate Zones 1 through 3. IECC added the same requirements in its 2012 version. (Figure 1 shows the ASHRAE climate zone map for the U.S.)

There is, however, an ongoing debate about whether cool roofs deliver net energy benefits in northern climates that experience cold winters and warm to hot summers (Climate Zones 4 through 8). Do reflective roofs remain beneficial as the cold weather season kicks in? The same properties that allow reflective roofs to keep buildings cooler in the summer may also cause them to make buildings colder in the winter. Theoretically, buildings with cool roofs could require more energy to reach a comfortable temperature in winter—a consequence known as the “winter heating penalty.” Furthermore, building codes tend to require more roof insulation in colder climates than warmer climates, potentially reducing the energy-efficiency benefits of roof surface reflectivity.

FIGURE 2A: Annual energy-cost savings ($1 per 100 square meters) from cool roofs on newly constructed, code-compliant buildings with all-electric HVAC. SOURCE: Energy and Buildings

FIGURE 2A: Annual energy-cost savings ($1 per 100 square meters) from cool roofs on newly constructed, code-compliant buildings with all-electric HVAC.
SOURCE: Energy and Buildings

The “winter heating penalty” and the impact of insulation are considerations when installing reflective roofs in some cold climates, but their negative effects are often greatly exaggerated. The sun is generally at a lower angle and days are shorter in winter months than summer months. In fact, in northern locations winter solar irradiance is only 20 to 35 percent of what is experienced in summer months, which means the sun has a reduced impact on roof surface temperature during the winter. Heating loads and expenditures are typically more pronounced in evenings, whereas the benefit of a darker roof in winter is mostly realized during daylight hours. Many commercial buildings require space cooling all year because of human activity or equipment usage, thereby negating the little—if any—heating benefit achieved by a dark roof.

Two new studies, along with decades of real-world examples from the marketplace, indicate that reflective roofs are an effective net energy (and money) saver even in our coldest cities.

SNOW’S IMPACT

In a study recently published in Energy and Buildings, researchers from Concordia University in Montreal evaluated the energy-consumption impact of adding cool roofs to a number of retail and commercial buildings in Anchorage, Alaska; Milwaukee; Montreal; and Toronto. The researchers looked at older, less insulated building prototypes, as well as newer buildings built with code-compliant levels of insulation. Unlike earlier work evaluating the impact of roof reflectivity on building energy consumption in cold climates, this new analysis also accounted for the impact of snow on the roof during winter months.

FIGURE 2B: Annual energy-cost savings ($1 per 100 square meters) from cool roofs installed on older buildings with all- electric HVAC. SOURCE: Energy and Buildings

FIGURE 2B: Annual energy-cost savings ($1 per 100 square meters) from cool roofs installed on older buildings with all- electric HVAC.
SOURCE: Energy and Buildings

Snow has two impacts on the roof that are relevant to understanding the true impact of roof surface reflectivity on energy consumption. First, snow helps insulate the roof. As a porous medium with high air content, snow conducts less heat than soil. This effect generally increases with snow density and thickness. Second, snow is white and, therefore, reflective. At a thickness of about 4 inches, snow will turn even a dark roof into a highly reflective surface (approximately 0.6 to 0.9 solar reflectance).

When snow is factored in, the benefits of cool roofs in cold climates be- come much clearer. Figure 2a shows the net energy savings and peak electricity reduction with and without snow for cool roofs installed on newly constructed, code-compliant buildings, assuming all-electric HVAC. Figure 2b shows savings from cool roofs installed on existing, older vintage buildings. The paper, available from the journal Energy and Buildings also includes results with gas HVAC systems.

INSULATION’S EFFECTS

Another argument often heard against reflective roofing in cold climates is that buildings in northern climates tend to have higher levels of roof insulation that reduce or negate the energy-savings impact of roof surface color. A new field study and model analysis of black and white roof membranes over various levels of insulation by the City University of New York and Princeton University and Princeton Plasma Physics Lab, the latter two of Princeton, N.J., clearly rebuts the “insulation versus reflectivity” tradeoff.

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Never Stop Learning

This year as I watch my friends and family send their little ones off to school, I, too, am starting a new educational journey. I’m taking piano lessons. I’ve wanted to play since I was a child but never had the opportunity. My husband heard me talk about wanting to play a few times, so he suggested giving me lessons and a piano as a gift for our first wedding anniversary.

I literally thought about it for a full day. I was completely touched that my husband wanted to help me accomplish a lifelong dream. However, did I really want to commit myself to something completely out of the ordinary? I learned to play the trumpet in middle school and played through high school, so I can read music—treble clef. I’ve never had to learn bass clef or how to make my left hand and right hand play different music at the same time. Could I do it? What if I’m the worst adult student my teacher has ever had?

I came to the realization that the accomplishments of which I’m most proud pushed me out of my comfort zone. Plus, how could I possibly say no to my husband when his gesture was so sweet? I’ve had one lesson so far and the idea of being able to coordinate my hands still seems a little like being able to rub my stomach while patting my head. However, I’m excited about the future and am hoping I’ll be playing well by the holidays!

Every issue of Roofing has an educational bent, but this issue may push you out of your comfort zone. For example, cool roofs have been a hot topic for many years. Conventional wisdom states cool roofs are not appropriate for northern climates. Kurt Shickman, executive director of the Washington, D.C.-based Global Cool Cities Alliance, will challenge that notion in “Cool Roofing”. He presents new evidence from several scientific studies that demonstrate cool roofs provide benefits to buildings in Climate Zones 4 through 8.

Meanwhile, Thomas W. Hutchinson, AIA, FRCI, RRC, CSI, RRP, principal of Hutchinson Design Group Ltd., Barrington, Ill., and a member of Roofing’s editorial advisory board, shares his in-the-field experiences regularly. He notes in “From the Hutchinson Files” that code-mandated insulation thicknesses are forcing designers to take roof access door and clerestory sill details seriously. Hutch’s goal with his article is to give designers some confidence to create appropriate design and detailing solutions.

These articles may challenge what you’ve always done but they’re worth considering and discussing. In fact, I’d really like to hear what you think about them. In return, I’ll keep you updated on whether I’m becoming the next Chopin!

The Building Industry Is Working to Reduce Long-term Costs and Limit Disruptions of Extreme Events

“Resilience is the ability to prepare for and adapt to changing conditions and to withstand and recover rapidly from deliberate attacks, accidents, or naturally occurring threats or incidents.” —White House Presidential Policy Directive on Critical Infrastructure Security and Resilience

In August 2005, Hurricane Katrina made landfall in the Gulf Coast as a category 3 storm. Insured losses topped $41 billion, the costliest U.S. catastrophe in the history of the industry. Studies following the storm indicated that lax enforcement of building codes had significantly increased the number and severity of claims and structural losses. Researchers at Louisiana State University, Baton Rouge, found that if stronger building codes had been in place, wind damages from Hurricane Katrina would have been reduced by a staggering 80 percent. With one storm, resiliency went from a post-event adjective to a global movement calling for better preparation, response and recovery—not if but when the next major disaster strikes.

CHALLENGES OF AN AGING INFRASTRUCTURE

We can all agree that the U.S. building stock and infrastructure are old and woefully unprepared for climatic events, which will occur in the years ahead. Moving forward, engineering has to be more focused on risk management; historical weather patterns don’t matter because the past is no longer a reliable map for future building-code requirements. On community-wide and building-specific levels, conscientious groups are creating plans to deal with robust weather, climatic events and national security threats through changing codes and standards to improve their capacity to withstand, absorb and recover from stress.

Improvements to infrastructure resiliency, whether they are called risk-management strategies, extreme-weather preparedness or climate-change adaptation, can help a region bounce back quickly from the next storm at considerably less cost. Two years ago, leading groups in America’s design and construction industry issued an Industry Statement on Resiliency, which stated: “We recognize that natural and manmade hazards pose an increasing threat to the safety of the public and the vitality of our nation. Aging infrastructure and disasters result in unacceptable losses of life and property, straining our nation’s ability to respond in a timely and efficient manner. We further recognize that contemporary planning, building materials, and design, construction and operational techniques can make our communities more resilient to these threats.”

With these principles in mind, there has been a coordinated effort to revolutionize building standards to respond to higher demands.

STRENGTHENING BUILDING STANDARDS

Resiliency begins with ensuring that buildings are constructed and renovated in accordance with modern building codes and designed to evolve with change in the built and natural environment. In addition to protecting the lives of occupants, buildings that are designed for resilience can rapidly re-cover from a disruptive event, allowing continuity of operations that can liter- ally save lives.

Disasters are expensive to respond to, but much of the destruction can be prevented with cost-effective mitigation features and advanced planning. A 2005 study funded by the Washington, D.C.-based Federal Emergency Management Agency and conducted by the Washington-based National Institute of Building Sciences’ Multi-hazard Mitigation Council found that every dollar spent on mitigation would save $4 in losses. Improved building-code requirements during the past decade have been the single, unifying force in driving high-performing and more resilient building envelopes, especially in states that have taken the initiative to extend these requirements to existing buildings.

MITIGATION IS COST-EFFECTIVE IN THE LONG TERM

In California, there is an oft-repeated saying that “earthquakes don’t kill people, buildings do.” Second only to Alaska in frequency of earthquakes and with a much higher population density, California has made seismic-code upgrades a priority, even in the face of financial constraints. Last year, Los Angeles passed an ambitious bill requiring 15,000 buildings and homes to be retrofitted to meet modern codes. Without the changes, a major earth- quake could seriously damage the city’s economic viability: Large swaths of housing could be destroyed, commercial areas could become uninhabitable and the city would face an uphill battle to regain its economic footing. As L.A. City Councilman Gil Cedillo said, “Why are we waiting for an earthquake and then committed to spending billions of dollars, when we can spend millions of dollars before the earthquake, avoid the trauma, avoid the loss of afford- able housing and do so in a preemptive manner that costs us less?”

This preemptive strategy has been adopted in response to other threats, as well. In the aftermath of Hurricane Sandy, Princeton University, Princeton, N.J., emerged as a national example of electrical resilience with its microgrid, an efficient on-campus power-generation and -delivery network that draws electricity from a gas-turbine generator and solar-panel field. When the New Jersey utility grid went down in the storm, police, firefighters, paramedics and other emergency-services workers used Princeton University as a staging ground and charging station for phones and equipment. It also served as a haven for local residents whose homes lost power. Even absent a major storm, the system provides cost efficiency, reduced environmental impact and the opportunity to use renewable energy, making the initial investment a smart one.

ROOFING STANDARDS ADAPT TO MEET DEMANDS

Many of today’s sustainable roofing standards were developed in response to severe weather events. Wind-design standards across the U.S. were bolstered after Hurricane Andrew in 1992 with minimum design wind speeds rising by 30-plus mph. Coastal jurisdictions, such as Miami-Dade County, went even further with the development of wind- borne debris standards and enhanced uplift design testing. Severe heat waves and brown-outs, such as the Chicago Heat Wave of 1995, prompted that city to require cool roofs on the city’s buildings.

Hurricane Sandy fostered innovation by demonstrating that when buildings are isolated from the supply of fresh water and electricity, roofs could serve an important role in keeping building occupants safe and secure. Locating power and water sources on rooftops would have maintained emergency lighting and water supplies when storm surges threatened systems located in basement utility areas. Thermally efficient roofs could have helped keep buildings more habitable until heating and cooling plants were put back into service.

In response to these changes, there are many opportunities for industry growth and adaptation. Roof designs must continue to evolve to accommodate the increasing presence of solar panels, small wind turbines and electrical equipment moved from basements, in addition to increasing snow and water loads on top of buildings. Potential energy disruptions demand greater insulation and window performance to create a habitable interior environment in the critical early hours and days after a climate event. Roofing product manufacturers will work more closely with the contractor community to ensure that roofing installation practices maximize product performance and that products are tested appropriately for in-situ behavior.

AVERTING FUTURE DISASTERS THROUGH PROACTIVE DESIGN

Rather than trying to do the minimum possible to meet requirements, building practitioners are “thinking beyond the code” to design structures built not just to withstand but to thrive in extreme circumstances. The Tampa, Fla.-based Insurance Institute for Business & Home Safety has developed an enhanced set of engineering and building standards called FORTIFIED Home, which are designed to help strengthen new and existing homes through system-specific building upgrades to reduce damage from specific natural hazards. Research on roofing materials is ongoing to find systems rigorous enough to withstand hail, UV radiation, temperature fluctuations and wind uplift. New techniques to improve roof installation quality and performance will require more training for roofing contractors and more engagement by manufacturers on the installation of their products to optimize value.

Confronted with growing exposure to disruptive events, the building industry is working cooperatively to meet the challenge of designing solutions that provide superior performance in changing circumstances to reduce long-term costs and limit disruptions. Achieving such integration requires active collaboration among building team members to improve the design process and incorporate new materials and technologies, resulting in high-performing structures that are durable, cost- and resource-efficient, and resilient so when the next disruptive event hits, our buildings and occupants will be ready.

North American Cities Are Implementing Urban Heat Reduction Strategies, Including Cool Roofing

A survey of North American cities by the American Council for an Energy Efficient Economy (ACEEE) and the Global Cool Cities Alliance (GCCA) finds that confronting the challenges of extreme weather, adapting to a changing climate, and improving the health and resiliency of urban populations are driving cities to develop and implement strategies to reduce excess urban heat.

Nearly two-thirds of the cities surveyed cited local extreme weather events as a key reason for initiating urban heat island mitigation strategies. “U.S. cities are waking up to the growing threat of urban heat and employing a number of innovative approaches suited to their location and priorities,” said ACEEE researcher and report author Virginia Hewitt. “Our report will help local planners adapt these practices to even more communities across the country.”

ACEEE and GCCA surveyed 26 cities in the U.S. and Canada representing all of the major climate zones, geographies, and city sizes. Despite the diversity of the respondents, several common themes emerged. Local governments are “leading by example” by requiring use of “cool” technologies, such as reflective roofs on municipal buildings, lining city streets with shade trees, and raising public awareness. Additionally, more than half of the cities have some kind of requirement in place for reflective and vegetated roofing for private sector buildings. Almost every city had policies to increase tree canopy and manage storm water.

“Our report finds that by addressing their urban heat islands, cities are more effectively delivering core public health and safety services, making them attractive places to live, work, and play,” said Kurt Shickman, executive director of the Global Cool Cities Alliance.

The report includes case studies on how several cities have responded to urban heat, demonstrating the variety of strategies employed. In response to a study that found that Houston’s roofs and pavements can reach 160 F, the city now requires most flat roofs in the city to be reflective. After an extreme heat wave in 2008, Cincinnati lost much of its urban canopy, and instituted an aggressive forestry plan. Washington D.C., has instituted a wide suite of programs such as Green Alleys, which helps residents manage excess stormwater by replacing pavement with grass and trees, and requiring reflective roofs on all new buildings.

The survey also found that most city governments are not acting alone to reduce excess heat. States, neighboring jurisdictions, utilities, developers, contractors, and local building owners are collaborating to create incentives for communities to reduce urban heat and mainstream these practices.

“We recognized a number of years ago that keeping New York cooler was an important part of protecting public health and becoming more resilient. We started with cool-roof volunteer programs that raised awareness and understanding, while coating 5 million square feet of rooftops. These voluntary efforts led to the cool roof ordinance requiring investments in reflective roofs on certain buildings,” said Wendy Dessy of NYC Service.

Cities surveyed in the report include: Albuquerque, N.M.; Atlanta; Austin, Texas; Baltimore; Boston; Charlotte, N.C.; Chicago; Chula Vista, Calif.; Cincinnati; Dallas; Denver; Houston; Las Vegas; Los Angeles; Louisville, Ky.; New Orleans; New York; Omaha, Neb.; Philadelphia; Phoenix; Portland, Ore.; Sacramento, Calif.; St. Louis, Mo.; Toronto; Vancouver, British Columbia, Canada; and Washington, D.C.

View Cool Policies for Cool Cities: Best Practices for Mitigating Urban Heat Islands in North American Cities.

ERA Challenges LBNL Study about White Roofs

The Bethesda, Md.-based EPDM Roofing Association (ERA) is challenging a study released by Lawrence Berkeley National Laboratory, Berkeley, Calif., which cites white roofs as the most “cost-effective” roofing option over a 50-year time span. The study, published in the March 2014 issue of Energy and Buildings, also calls for the phase-out of black roofs.

“Our members make both black and white roofing membranes. We strongly oppose any recommendation that irresponsibly promotes the use of one of our products over another based on faulty science. We question the validity of this study since it is based on a sample size of only 22 roofs, and we are challenging the conclusions that the authors draw from the data,” says Ellen Thorp, ERA’s associate executive director. “Due to the complexity of roof and building science, prescriptive requirements that limit design choices are not in the best interests of architects, design professionals or building owners.”

To help provide clarity regarding roofing-system choice and refute some errors in the study, ERA convened a panel of experts to review the LBNL science and its conclusions. A complete analysis can be found on the ERA website.

Overall, the LBNL study was marked by “a systematic failure to understand that roofs are systems, not a single component,” says Thomas W. Hutchinson, AIA, FRCI, RRC, principal of Hutchinson Design Group Ltd., Barrington, Ill., an internationally recognized expert on roof system design and a Roofing editorial advisor. “Additionally, the study completely ignored
ballasted EPDM systems that, in other studies, have proven to be the roof system that provides the greatest service life and energy savings. To suggest that a comparatively ‘new’ roofing material will have a longer service life than EPDM, a material proven to last over 30 years, is naïve.”

“Our members—Firestone Building Products, Carlisle SynTec Systems and Johns Manville—have a vested interest in providing accurate information to our customers,” Thorp adds. “Their knowledge is based on marketing, installing and maintaining thousands of roofing systems. We hope that architects, specifiers and roofing consultants will continue to rely on their field-based knowledge about the comparative costs and effectiveness of roofing systems, rather than on flawed science based on flimsy and biased data.”

Benjamin Mandel, a research assistant in the Heat Island Group at LBNL and an author of the LBNL study, recently responded to ERA’s remarks on Today’s Facility Manager’s website.
Read Mandel’s reaction at bit.ly/1hcD0HR.