Cool Roofs in Northern Climates Provide More Bang for the Buck Than We Thought

Electricity demand in Washington, D.C., plotted against daily high temperature. Source: Weather Underground, PJM Interconnection (PJME).

(Figure 1) Electricity demand in Washington, D.C., plotted against daily high temperature. Source: Weather Underground, PJM Interconnection (PJME).

The energy savings from cool, reflective, roofs have long made them the go-to roof choice in warmer and temperate climates here in the United States. Both ASHRAE and the International Energy Conservation Code have included roof surface reflectivity requirements for a number of years. About half of all new flat roofs installed in the country are highly reflective and in some product categories white options outsell dark ones by a substantial margin. It is hard to argue with the notion that, where it is warm, the roofs should be white. While the building-level impacts of cool roofs in cool climates has been covered in the past, very little has been written about the broader economic benefits of cooler buildings and cities. When we include the economic impacts of factors like improved health, air quality, and energy savings, the case for cool roofs in cool climates looks even better.

The Benefits of Cool Roofs Go Way Beyond the Building

The building-level impacts of cool roofs are a central part of the discussion about whether they should be used in cold climates. However, it is also important to recognize the substantial co-benefits that come from installing cool roofs in terms of healthier and more comfortable people, improved productivity, better air quality, and increased economic prosperity. While the economic benefits of cool roofs are substantial, they may not always be fully included in a building owner’s roof buying decision.

How much cooler could our cities become if we added more reflective roofs? In a comprehensive review on this topic, Santamouris 2012 found that when a global increase of the city’s albedo is considered, the expected mean decrease of the average ambient temperature is close to 0.5°F (0.3°C) per 0.1 increase in reflectivity, while the corresponding average decrease of the peak ambient temperature is close to 1.6°F (0.9°C). The cooling impact of reflective roofs in certain neighborhoods could be significantly better, though. A study of Chicago by Notre Dame University found that installing reflective roofs cooled city surfaces by around 3.5 to 5.5°F (2-3°C), but surfaces in the downtown core cooled by 12.5 to 14.5°F (7-8°C).

Cool Cities Are Energy Savers

We have started to better understand and quantify the impact in cities that are able to get a degree or two of cooling. The most obvious benefit is that cooler cities demand less energy on hot days. The graph in Figure 1 plots electricity demand in

Lowering the temperature of cities can bring a multitude of benefits. Source: Global Cool Cities Alliance.

(Figure 2) Lowering the temperature of cities can bring a multitude of benefits. Source: Global Cool Cities Alliance.

Washington, D.C., against the maximum temperature every day for 5 years (2010–2015). The graph’s shape looks very similar to plots from other cities with high penetrations of air conditioning units. Demand for electricity climbs rapidly above about 80°F. When the maximum temperature is 90°F, the city requires 21 percent more electricity, on average, than on 80°F days. At 95°F, demand has spiked by nearly 40 percent over the 80°F baseline. Charges for peak electricity demand are a major expense for commercial and industrial building operators and, in seventeen states, for homeowners as well. Further, peaking demand is often met by less efficient, more expensive, and dirtier power plants that worsen air quality. At worst, peak demand can cause productivity-killing service interruptions or brownouts.

Cooler Cities Are Healthier Places

Heat is a potent but silent killer. On average, heat kills more people than any other natural disaster, and heat-related deaths tend to be underreported. In 2015, Scientific American reported that 9 out of the 10 deadliest heat events in history have occurred since 2000 and have led to nearly 130,000 deaths. Cities on dangerously hot days experience 7 percent to 14 percent spikes in mortality from all causes.

Heat stress and stroke are only the tip of the pyramid of heat health impacts. Heat puts significant additional stress on people already suffering from diseases of the heart, lungs, kidneys, and/or diabetes. A recent study finds that every 1.5°F increase in temperatures will kill 5.4 more people per 100,000 people every year.

Installing cool roofs or vegetation can lead to a meaningful reduction in heat deaths by making the daytime weather conditions more tolerable. There are a number of studies estimating the impact of increasing urban reflectivity and vegetative cover on weather conditions. Kalkstein 2012 and Vanos 2013 looked at past heat waves in 4 U.S. cities and modeled the impact of increasing reflectivity by 0.1 (the estimated equivalent of switching about 25 percent of roofs from dark to light colors) and vegetative cover by 10 percent. Though the sample sizes are too small to draw sweeping conclusions, the studies found that cities making these modest changes could shift weather into less dangerous conditions and reduce mortality by 6 percent to 7 percent.

Cooler Cities Are Engines of Economic Growth

The health, air quality, and energy benefits of modest increases in urban roof reflectivity could generate billions of dollars of

An infrared scan of Sacramento, Calif., shows the range of surface temperatures in the area. Source: Lawrence Berkeley National Laboratories.

(Figure 3) An infrared scan of Sacramento, Calif., shows the range of surface temperatures in the area. Source: Lawrence Berkeley National Laboratories.

economic prosperity for our cities. A study of 1,700 cities published in the Journal Nature Climate Change found that changing only 20 percent of a city’s roofs and half of its pavement to cool options could save up to 12 times what they cost to install and maintain, and reduce air temperatures by about 1.5°F (0.8°C). For the average city, such an outcome would generate over a $1 billion in net economic benefits. Best of all, adding cool roofs to between 20 and 30 percent of urban buildings is a very realistic target if existing urban heat island mitigation policy best practices are adopted.

Cool Roof Performance in Cold Climates: In Brief

As positive as cool roofs are for cities in cool climates, they first have to be a high-performing choice for the building itself. What do we know about net energy savings in cool climates with higher heating load? This question was the subject of “There is Evidence Cool Roofs Provide Benefits to Buildings in Climate Zones 4-8” in the November/December 2016 issue of Roofing that summarized the newest science and field studies that show that reflective roofs provide net energy benefits and favorable heat flux impacts on roofs in cold climates. In short, the newest research from Columbia, Princeton and others demonstrates that the size of the “winter heating penalty” is significantly less than many had thought and shows net reductions in annual energy use when cool roofs are used, even with roof insulation levels as high as R48.

Real Cool Roofs in Cold Climates: The Target Survey

It is not just the science that supports the use of reflective roofs in cold climates. The strong and steady growth of cool roofing in northern markets over the last decade or two is also a good indication that reflective roofs are a high-performance option in those areas. For almost 20 years, Target Corporation has installed reflective PVC membranes on nearly all of its stores in the

Studies estimate that modest increases in urban roof reflectivity could generate billions of dollars of economic prosperity for cities. Pictured here is the roof on the Cricket Club in Toronto. Photo: Steve Pataki

Studies estimate that modest increases in urban roof reflectivity could generate billions of dollars of economic prosperity for cities. Pictured here is the roof on the Cricket Club in Toronto. Photo: Steve Pataki

United States and Canada. The membranes are usually installed over a steel deck with no vapor retarder. Target and manufacturer Sika Corporation undertook a field study of 26 roofs on randomly chosen stores located in ASHRAE Climate Zones 4-6 including Connecticut, Illinois, Massachusetts, Michigan, Minnesota, New York, Washington, and Wisconsin. The roofs were 10-14 years old at the time of the survey. None of the 51 total roof sample cuts were made across these roofs showed signs of condensation damage. A more detailed accounting of the study by representatives of Target Corporation and Sika Sarnafil published in Building Enclosure includes this important paragraph from authors Michael Fenner, Michael DiPietro and Stanley Graveline:

“Specific operational and other costs are confidential information and cannot be disclosed. However, it can be stated unequivocally that although the magnitude varies, Target has experienced net energy savings from the use of cool roofs in all but the most extreme climates. Although the savings in northern states are clearly less than those achieved in southern locations, experience over approximately two decades has validated the ongoing use of cool roofs across the entire real estate portfolio. Even in climates with lengthy heating seasons, overall cooling costs exceed heating costs in Target’s facilities.”

It is increasingly clear that installing cool roofs is the definition of “doing well by doing good.” Even in cold areas, a properly built roof system with a reflective surface is a high-performance option that delivers value for building owners while making hugely positive contributions to the neighborhoods and cities they occupy.

North Carolina Middle School Generates More Energy Than It Uses

Sandy Grove Middle School in Hoke County, N.C.

Sandy Grove Middle School in Hoke County, N.C., was designed to be an energy-positive building. It generates 40 percent more energy than it consumes. Photo: Mathew Carbone Photography

When Robbie Ferris first presented the idea of a school building that generates more energy than it uses, people were skeptical. Now he can point to Sandy Grove Middle School in Hoke County, N.C., as proof that a high-performance school building can go well beyond net zero and generate 40 percent more energy than it consumes.

Ferris is the president of SfL+a Architects and manager at Firstfloor, a development company that specializes in public-private partnerships and design-build-operate agreements. “We designed the building, we own it and we lease it to the school district,” he says. “We monitor all of the systems remotely. One of the reasons we do that is because when you put really high-performance systems in buildings, you have to make sure they are operating at peak efficiency. It can take time to make sure everything is optimized.”

Three years after completion, Sandy Grove Middle School is outperforming its energy models, and the building continues to win accolades. It recently received Energy Star 100 Certification and has been recognized as the nation’s most energy positive school.

“Sandy Grove Middle School is a perfect example of a high-performance facility,” says Ferris. “With the public-private lease-back model, everyone wins. The students receive a quality school, it fits in to the school system budget, and it is energy efficient to help both total cost and our environment.”

The building’s systems were designed to be as energy-efficient as possible, and that includes the roof, which features an array of photovoltaic (PV) panels to generate electricity. “We wanted a roof that would last 30 years,” Ferris notes. “We’ve had a tremendous amount of success with TPOs, and metal roofs as well. This particular client wanted a metal roof look from the front, but they were very open to a membrane roof on other parts of the building. We made the decision to put the metal roof on the front of the building and a TPO on the wings at the back of the building.”

On this project, the warranties were important considerations, along with durability and energy efficiency. SfL+a specified a standing seam metal roof system manufactured by Dimensional Metals Inc. and a TPO system manufactured by GenFlex. “Obviously, if you’re putting a couple of million dollars’ worth of solar panels on your roof, you want to make sure you have a roof that is going to be problem free.”

A Smooth Installation

The installation was a challenging one, but everything went smoothly, notes Aaron Thomas, president and CEO of Metcon Inc. Headquartered in Pembroke, N.C., Metcon is a full-service general contractor that specializes in energy positive commercial buildings, so it was perfectly suited to serve as the construction manager on the project.

Photovoltaic panels were installed

Photovoltaic panels were installed on both the standing seam metal roof and the TPO system. The systems on the low-slope roof sections are fully ballasted, and both sections were installed without penetrating the roof system. Photo: SfL+a Architects

Thomas and Ryan Parker, senior project manager with Metcon, coordinated the work of subcontractors on the job, including the Youngsville, N.C. branch of Eastern Corp., which installed the TPO and metal roofs, and PowerSecure, the solar installer on the project, based in Wake Forest, N.C.

The roof systems covered 85,000 square feet, and Sharp PV panels were installed on both the metal roof and the TPO system. Solar panels were also installed on freestanding structures called “solar trees.” Each solar tree is 20 feet tall, 25 feet wide and weighs 3,200 pounds.

“The TPO roof system was upgraded to an 80-mil product due to solar panels being added to the roof,” Parker notes. “It was 100 percent ballasted on the low-slope sections, with slip sheets being used below the racking on the TPO roof.”

On the metal roof, clips manufactured by S-5! were used to affix the solar racking to the seams. “There are no penetrations for the frames, and penetrations for the electrical wiring went through vertical walls, not the roof,” Parker says. “There were no penetrations anywhere in the roof system, which made all of the warranties that much easier to keep intact.”

The biggest challenges on the project, according to Parker, were coordinating the different scopes of work and ensuring all of the manufacturers’ warranty considerations were met. “We had two different kinds of roofs, both coupled with solar panels,” Parker says. “Like any rooftop with photovoltaic products, there had to be special attention paid to the warranties of all parties involved. Both Genflex and DMI were closely involved in coordinating details to ensure that the owner achieved a great roof free of defects.”

The building’s systems were designed for energy efficiency

The building’s systems were designed for energy efficiency, and the roof features an array of photovoltaic panels to generate electricity. Photo: Mathew Carbone Photography

One key was developing a detailed schedule and keeping everyone on it. “We would meet once a week and huddle up on how it was progressing and what else needed to be done,” Parker recalls. “We found that by using a collaborative submittal sharing platform, all of the varying parts and pieces could be checked by all parties to ensure compatibility.”

There were multiple safety concerns associated with combining solar panels to the roofing system, so everyone had to be on the same page. “The roofing subcontractor and the solar subcontractor performed a joint safety plan that utilized common tie off points,” Parker notes. “The job had zero lost time.”

“Everyone coordinated their work and it was a great team effort,” Ferris says. “It was one of the smoothest jobs I’ve ever seen. We have not had a single leak on that project—not a single problem.”

Proof Positive

For Ferris, the greatest obstacle on energy-positive projects convincing members of the public and governmental agencies of the benefits. “The biggest challenges had nothing to do with construction; they had to do with just doing something new and different,” he says. “The toughest challenge was getting the school board, the county commissioners, the public and the review agencies on board. It took a very long time—and lots of meetings.”

Photo: SfL+a Architects

Now Ferris can point to Sandy Grove as an example of just how a high-performance school building can pay huge dividends. “As soon as you see it in real life, you’re on board,” he says. “It’s very exciting for people to see it. If we can get people to the school, they’ll walk away convinced it is the right thing to do.”

With Sandy Grove, the school district has a 30-year lease with an option to purchase. Ferris believes the lease model is the perfect solution for educators. “We’re responsible for any problems for the life of the lease,” he says. “If a problem does come up, we usually know about it before the school does because we monitor the systems remotely online.”

“In their world, buildings are a distraction from educating kids,” Ferris concludes. “This is one building that is not a distraction.”

TEAM

Building Owner: Firstfloor, Inc., Winston-Salem, N.C., Firstfloor.biz
Architect: SfL+a Architects, Raleigh, N.C., Sfla.biz
Construction Manager: Metcon Inc., Pembroke, N.C., Metconus.com
Roofing Contractor: Eastern Corp., Youngsville, N.C.
Photovoltaic Panel Installer: PowerSecure, Wake Forest, N.C., Powersecure.com
Metal Roof System Manufacturer: Dimensional Metals Inc., DMImetals.com
TPO Roof System Manufacturer: GenFlex Roofing Systems, GenFlex.com

Duro-Last Single-Ply Roofing Membranes Earn Platinum Certification

Duro-Last announces that it has achieved platinum certification under the NSF American National Standard for Sustainable Roofing Membranes, NSF/ANSI 347. Certified by UL, this standard represents that Duro-Last manufactures a product that is third-party verified as sustainable, durable, and high performing. The certification applies to 40, 50 and 60 mil, white, tan, gray and dark gray as well as 50 mil terra cotta Duro-Last membranes.
 
“Duro-Last was excited to have most of our membrane product lines certified by this third-party standard,” says Jason Tunney, executive vice president and general counsel of Duro-Last. “But we wanted to take it to the next level and achieve the highest rating possible.”
 
NSF/ANSI 347 was written by NSF International and, according to their website, is based on life-cycle assessment principles. NSF/ANSI 347 employs a point system to evaluate roofing membranes against established prerequisite requirements, performance criteria and quantifiable metrics in five key areas:

  • Product design
  • Product manufacturing
  • Membrane durability
  • Corporate governance
  • Innovation

 
Obtaining this certification will help the Duro-Last membrane meet the market demand for products that comply with green building standards like the Green Building Initiative’s Green Globes. Product specifiers and purchasers are under pressure to find products that meet their sustainability criteria, and having the NSF 347 certification can give them the peace of mind of specifying a third-party verified product.
 
This certification is one more step in Duro-Last’s commitment to sustainability and transparency, coming after the announcement of the publication of Environmental Product Declarations (EPDs) for Duro-Tuff, Duro-Fleece and Duro-Last EV membranes. To read more about Duro-Last’s sustainability efforts, visit here.
 
“There’s talk in the roofing industry about being ‘green’ and sustainable,” says Katie Chapman, Duro-Last corporate sustainability specialist. “At Duro-Last we want to help people make informed decisions when purchasing roofing products.”
 
For more information regarding Duro-Last’s sustainability initiatives contact Katie Chapman at (800)248-0280 or kchapman@duro-last.com.

Standard for the Design of High-Performance Green Buildings Is Open for Public Review

Changes to the purpose and scope that reflect advances in green buildings over the last 10 years are proposed for the high performance building standard from ASHRAE, the International Code Council (ICC), the U.S. Green Building Council (USGBC) and the Illuminating Engineering Society (IES).

ASHRAE/IES/USGBC/ICC Standard 189.1, Standard for the Design of High-Performance Green Buildings, contains minimum requirements for the siting, design and construction of high-performance green buildings in support of reducing building energy use, resource consumption and other environmental impacts while maintaining acceptable indoor environments.

Among them is addenda o, which proposes revisions to the existing purpose and scope of the standard to clarify its intended purposes and application, and to better reflect the revisions to the standard that are being considered by the committee.

Committee chair Andrew Persily notes that the current title, purpose and scope were approved in 2006 and that much has taken place in the world of green buildings in the past 10 years.

Under addenda o, the purpose of the standard has been rewritten to focus on goals vs. strategies. For example, rather than energy efficiency, the goal of reduced building emissions is proposed for inclusion in the purpose.

A new section of the purpose speaks to the alignment of Standard 189.1 with the International Green Construction Code (IgCC), noting specifically that the standard is intended to serve as the technical basis of mandatory buildings codes and regulations for high-performance buildings.

Standard 189.1 currently is a compliance option of the 2015 IgCC, published by the International Code Council, ASTM and the American Institute of Architects. The standard will serve as the technical content for the IgCC beginning in 2018.

Other addenda open for public review until May 8, 2016 are:

  • Addendum i reorganizes the roof heat island mitigation section and adds new provisions for vegetated terrace and roofing systems relative to plant selection, growing medium, roof membrane protection and clearances. In addition, provisions for the operation and maintenance of vegetated roofs are proposed for addition to Section 10.
  • Addendum n clarifies footnote b to Table 7.5.2A. This footnote provides a method to adjust the percent reduction for buildings with unregulated energy cost exceeding 35 percent of the total energy cost. This addendum clarifies that the adjustment is to be made on the basis of energy cost, not energy use.
  • Addendum p proposes to add requirements for water bottle filling stations, which are intended to improve water efficiency and sanitation of public drinking water and to reduce the environmental effects of plastic bottles.
  • Addendum r lowers the ductwork pressure testing threshold to include 3-inch pressure class ducts, which are common upstream of variable air volume (VAV) boxes.
  • Addendum t adds new requirements for reverse osmosis and onsite reclaimed water systems in order to reduce the likelihood of excessive water use because of poor design of water treatment and filter system.
  • Addendum u adds new requirements for water softeners to reduce water consumption given the impact of the design and efficiency of these systems on water discharge water rates.

Open for public review from April 8 until May 23, 2016 are:

  • Addendum q modifies Chapters 5, 7, 8 and 11, as well as Appendices A and E, to reflect the addition of Climate Zone 0 in ANSI/ASHRAE Standard 169-2013, Climatic Data for Building Design Standards.
  • Addendum s removes the performance option for water use and moves the prescriptive option into the mandatory section.