What’s Next for Cool Roofs?

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In July 2010, Secretary of Energy Steven Chu launched an initiative to install cool roofs on DOE and government buildings. Recognition of the benefits of cool roofs like those from Conklin and the development of emerging technologies promises to transform the future marketplace. Several laboratories, universities and companies are already conducting research on new cool roof products, from self-cleaning to thermally sensitive materials to solar panels that take advantage of cool roofs.

Although they may seem like conflicting technologies, cool roofs can be complimentary to solar photovoltaic panels. According to the DOE, a cool roof can keep the roof surface 50% cooler than a dark roof under the same conditions. Solar panels may perform more efficiently and for a longer lifespan under the cooler conditions provided by a cool roof. Panels by California solar photovoltaic manufacturers Solyndra have even been developed with curved surfaces to take advantage of light refracted off the cool roof.

The Lawrence Berkeley National Laboratory’s Heat Island Group is conducting research on the effects of dirt and algae on the roof surface over time, and it is working to develop an accelerated aging process. This can significantly decrease the aged testing timeline, allowing roofing manufacturers to design and improve product formulas without waiting three years for the aged performance. The Heat Island Group is also working on a self-cleaning surface for roofing materials to reduce the effects of weathering on solar reflectance values. The scientists at United Environment and Energy LLC are developing a coating that can recognize temperature changes to either reflect or absorb solar energy depending on what would be more advantageous for the building. The coating is created using waste cooking oil from restaurants and can be adapted to different climates with preset temperature thresholds. A team at the Massachusetts Institute of Technology has focused on a similar concept, designing a roof tile that changes colors according to temperature. The tiles are made of common polymers encapsulated by a clear plastic top layer and black back layer. These are just a few examples of new technologies that are pushing roofing materials to have the ability to maintain high-performance after weathering while decreasing both cooling and heating loads for a building.

Despite the benefits of cool roofing, it is still a ways off from being adopted as a standard building practice. In the U.S., it faces barriers from misconceptions, aesthetic design concerns and moisture issues caused by non-comprehensive installations. Yet, cool roofing is a simple design measure that can provide significant energy savings and environmental rewards. The Lawrence Berkeley National Laboratory’s Heat Island Group estimates that buildings with cool roofs use up to 40% less cooling energy than buildings with dark colored roofs. A designer specifying a rooftop now has several resources available to make informed and confident cool roof choices.

With increasingly rigorous roofing code and program standards, and promising emerging technologies on the horizon, cool roofs are quickly becoming one of the most effective ways to save energy and help mitigate global warming.

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Cool Roof Resources

There are thousands of product options just for cool roofing (including Conklin), so specifying an appropriate roof can be a daunting task. Cool roofs are available in all colors for virtually every roofing type, although white is still the most efficient option.

You can gauge the energy performance abilities by understanding how a cool roof reflects and emits the sun’s heat back to the sky instead of transferring it to the building below. Once you understand the basic technology of cool roofing, there are several resources available to help you make a confident, informed decision on your next project.

Solar reflectance and thermal emittance are the two key metrics determining how “cool” a roof will stay by its ability to reflect solar energy and emit absorbed heat. Solar reflectance and thermal emittance will appear as a value between 0 and 1, with a higher value signifying a “cooler” roof. Solar Reflectance Index (SRI) is a third metric that is calculated using a product’s solar reflectance and thermal emittance values. It is measured on a scale of 0 to 100 with a higher number symbolizing a more energy-efficient roof. SRI is sometimes used by code bodies or green building programs in place of solar reflectance and thermal emittance as a single-value alternative. Cool roof standards often specify higher reflectance requirements for low-slope, flat rooftops versus steep-slope, pitched rooftops. This difference in values is due to the energy impact the surface type faces, as the flat surface of a low-slope rooftop is exposed to greater solar radiation than a pitched roof.

Another factor in which roofing products are unique is that they are exposed to outdoor conditions that may alter the energy performing ability of the product. Each product is therefore tested initially as available straight off the shelf, as well as after it has been weathered by outdoor elements. A study by the Oak Ridge National Laboratory and DLR consultants found that the loss of effectiveness of solar reflectance for most roof types leveled out at around three years, so it is an industry standard to test roofing materials after three years of aging to determine their aged value. Code bodies sometimes reference this aged value, as it more accurately reflects the performance of the roof through its life cycle.

The Cool Roof Rating Council (CRRC) is a third-party rating program that works with manufacturers to rate their products’ solar reflectance and thermal emittance. The Rated Products Directory is a free online database of roofing products rated by the CRRC. Code bodies and voluntary green building programs define a cool roof by specifying a minimum value for initial and aged solar reflectance, thermal emittance and SRI, or a combination thereof. The CRRC does not set minimum standards for products to be listed on its Rated Products Directory, but provides unbiased and credible ratings for all products. You can search through more than 2,000 products by categories such as material type, color or manufacturer. You can even search by minimum initial or aged solar reflectance, thermal emittance or SRI value in order to fine-tune your search to products that meet a specific code or program standard.

While code bodies set cool roof minimum standards as guidelines, many people find it more realistic to specify a cool roof based on quantifiable benefits. The U.S. Department of Energy (DOE) and the Environmental Protection Agency (EPA) have both created cool roof calculators to determine energy and monetary savings based on climate, building size, HVAC equipment and other important factors.

• The DOE Cool Roof Calculator offers savings estimates for small- and medium-sized facilities with flat roofs.
• The EPA Roof Savings Calculator is designed for both residential and commercial buildings, and it allows you to define information about your existing and proposed roofs for comparison.

The cool roof calculators show the tangible savings gained from cool roofs, yet cool roofs offer several other environmental benefits. Eco-conscious designers may also want to consider the cradle-to-cradle aspects of their material choices, including recycled content, end of life recyclability and toxicity of materials.

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Roof Specification and Installation

Building owners and facilities or maintenance managers need to take into account the importance of quality assurance during roof system installation. Typically, quality assurance is provided by the roofing contractor, who is responsible for installing the roof according to the contract.

Many times a lack of supervision, training or poor crew morale can result in poor quality roof installation. On the other hand, hiring an outside roof-system design professional (an architect, engineer or roof consultant) can help a manager ensure quality control.

It is recommended in most cases that someone with roofing experience be on the jobsite throughout the duration of the project. Sometimes it is best to get a design professional involved early on in the project, possibly even having a designer prepare a job-specific detailed specification. This way the designer is familiar with the project from beginning to end and can control the installation of the roof system.

Even little things, such as making sure the contractor is using the materials specified for a particular job and using the correct amount of fasteners, asphalt or adhesives is important in ensuring a quality finished product. Using this type of professional enables managers to have an expert design a detail for those unique situations on a roof.

Although roofers are good at figuring out difficult details, others might simply throw materials together and call it "watertight". Some manufacturers can assist in selecting a particular roof system and preparing a site-specific specification. But other manufacturers merely push their product, which might or might not meet the needs of a particular building or facility.

A roof system design professional, on the other hand, has the knowledge of a wide variety of roofing manufacturers and roofing systems in the market. The designer will specify a roof that fits the needs and uniqueness of a given building and can offer a list of manufacturers from which to choose.

The specifier will design specific details for your building where a roofing contractor or manufacturer may overlook or try to get by with an inadequate standard detail.

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Preventing Premature Roof Failures

The way a roof wears can show a lot about why it is failing. Each type of failure, whether it be blisters, splits or punctures (just to name a few) typically results from a specific cause. For example, poor design can lead to splits and debris can cause punctures. Understanding the causes of the most common types of roof problems can help building owners and facility managers prevent the errors that too often shorten the life of the roof.

Preventing problems begins with the design of the roof and choice of materials. The roof membrane chosen should reflect the characteristics of the building. If there will be a lot of foot traffic, you should choose a system that will be resistant to such damage. If the roof is wide open and there will be a great deal of thermal movement, a stretchable material such as an EPDM membrane is a better choice than a system that has limited elongation capabilities.

Details must be carefully thought out prior to installation. A transition from a gravel stop to a parapet is a poor building design that must be compensated for in the roof design. A metal transition piece can help alleviate problems that occur as a result of differential movement and different directional movement between the gravel-stop portion and the parapet portion. Correcting slope-to-drain problems should be determined at the design stage.

The roof must also be properly installed, using dry materials and installing them according to the design details or manufacturer’s requirements. Expansion joints have to terminate in a way that the end of the joint will still compensate for building movement. This means that there should be no material crossing the joint — not gravel stops, copings, membrane, and certainly not roofing cement — that cannot flex or move with the movement of the structure. All seams should be properly adhered.

Finally, the roof must also be properly maintained. Roof access should be limited to only those who need to be up there. Keep smokers, lunches and sunbathers off the roof. Not only will the cigarettes burn holes in the membrane, the foot traffic will damage the surface and cause the roof to fail prematurely. Building owners and managers should monitor the activity of sign installers and window washers to be sure that they are not damaging the roof as they work. New HVAC installations should be flashed not by the mechanical contractor, but by a competent roofing contractor to be sure that the penetrations are sealed.

The roof itself should be examined twice a year, including having the drains cleared and all roof debris removed. All small problems like punctures and sealant failures should be addressed at this time to be sure that they are not causing problems that will lead to failure. The life of a roof is finite, but it doesn’t have to be short-lived. Some common sense when designing the roof, attention to detail when installing it, and care when using it will maximize its life.

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5 More Reasons Roofs Fail

Wrinkles

Wrinkles can occur both in the flashings and within the membrane itself. When there is differential movement between the roof deck and the perimeter, the flashings will wrinkle on a 45-degree angle. When a wrinkle reaches the edge of a membrane or flashing, the opening left at the end of the wrinkle is called a fishmouth because of its bass-mouth-like appearance. Depending on the ply in which the wrinkle occurred, the fishmouth can be a tunnel for water to get down into the building.

Wrinkles within the membrane will eventually fatigue and crack. Because they are raised above the surface of the roof, they are more prone to traffic damage, scuffing and surfacing loss than the rest of the roof.

Flashings

Flashings must be fastened at the top to prevent the membrane from slipping down the wall or curb, or to keep the membrane from creating a funnel into the building. A flashing normally terminates under a metal counterflashing. If it does, the counterflashing can create problems if the top is not properly sealed or the sealant has failed. If the metal counterflashing does not lap the membrane enough, it may fail to divert water from the flashing and instead funnel water into it.

Surfacings
Surfacings (like those from Conklin) on membranes may provide protection from ultraviolet radiation and damage from traffic on the roof. They also may be a component of the fire rating of the roof. In the case of ballasted roofs, surfacings may be the only thing keeping the roof in place other than gravity. When the surfacing gets displaced or worn off, either from foot traffic, repair persons, wind, etc., this protection no longer applies.

Fasteners
In mechanically attached roofing systems, movement from wind will cause fasteners to rock back and forth with the gusts.

Eventually, this movement causes the hole in the deck around the fastener to enlarge and the fastener to back out. The fastener heads can eventually puncture the membrane from below. But fastener back-out is not limited to single-ply membranes. It is also a common occurrence in metal roofing and in metal accessories on membrane roofs. In these cases, the backed-out fasteners leave holes where water can directly enter the building. This is an especially serious problem when a coping — the metal cap on the top of a parapet — is fastened through the top of the horizontal portion and not through the vertical flanges.

Abuse and Neglect
When it comes to mistreating a roof, the most common culprits are air conditioning and maintenance technicians, window washers, and sign installers. It is not unusual to see debris — ranging from screws and bits of sheet metal all the way up to empty refrigerant canisters and abandoned HVAC units — left on roofs after an air conditioning repair visit.

Small debris can cut into the roof if the debris is stepped on; large debris will work its way into the roof membrane during the hot months of the year. Sign installers routinely install conduit through the walls without properly sealing the penetrations. The water that gets into those penetrations works its way through the walls and into the building, disguised as a roof leak. Window washers and painters hang access equipment over the side of the roof, kick flashings and damage parapets, allowing leaks to occur. All of these groups of people can wreak havoc on base flashings, which get kicked, punctured with tools and machinery, and have mechanical equipment run up against them.

Owners contribute to the early demise of their own roofs by not properly maintaining them and failing to repair small problems, before they become big ones.

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5 Reasons Roofs Fail

Blisters

Bubble-like or long, thin raised areas on the roof are called blisters. Blisters are the most common roofing problem. They occur when a gas, usually water vapor, is trapped within the roofing system either between the plies or between the plies and the insulation. The heat of the sun during the day causes the gas to expand. The expansion of the gas creates a pressure within the system that pushes the plies apart, resulting in the blister.

Blisters would not occur if there were not some reason for moisture in the membrane. Two common ones are applying the roof to a damp substrate, as during a re-cover, and applying wet materials, such as felts, that have absorbed dew or rain on the edges. The moisture that causes blisters can often be traced back to another problem: improper storage of insulation, which allows water to soak through holes in shrink wrap or at the bottom of the stack where shrink wrap doesn’t cover. Moisture can also get into a roof installed in the presence of rain, snow or dew.

Open laps
Open laps in the field membrane, but especially in the flashings, are another problem. Open laps are just carelessness on the part of the installer. Usually it means that the installer has failed to apply adhesive to the entire lap. Sometimes it is caused in built-up and modified-bitumen systems when the bitumen is applied too cold. The laps appear to be closed, but open up as the roof ages.

In single-ply membranes, open laps are usually caused by improper surface preparation, such as adhering to a dirty membrane, heat welding at too cold of a temperature, not allowing the adhesive to dry properly or applying too much or too little adhesive.

Splitting
The most common splits occur when a metal accessory is flashed with a membrane material. As the temperature changes, metals and membranes expand and contract at very different rates. Because the membrane generally cannot move as much as the metal, it will eventually fatigue and crack when it is adhered to metal. This problem is not as common with single-ply membranes with better expansion and contraction capabilities, but it is common in asphalt and coal tar systems.

Splits occur frequently in expansion joints. Contractors rarely know how to properly terminate an expansion joint cover. They run it to the wall and stop it dead. Unfortunately, the movement in the building does not stop at the end of the expansion joint and, consequently, it rips open any attempt to seal that edge. Splits are also common at joints within the expansion joint cover itself.

Splits are not limited to flashings, however. As most roofs age, they become more brittle and less resilient. This means that they become less resistant to movement from common sources such as temperature changes, foot traffic and substrate movement. Because the roof cannot flex or stretch as well as it did when new, it cracks.

Punctures
The most preventable failure symptom, punctures usually occur because of carelessness on the part of people visiting the roof: HVAC technicians, window washers, painters, maintenance staff, smokers and tenants. Punctures can also occur because of debris left, blown or tossed on the roof. They may appear as tears or holes.

Penetrations
Another common failure location is penetrations. Of particular concern are pitch pans. There are three failures common to pitch pans: the sealer itself, the container in which it sits and the penetration to which the sealant is supposed to adhere. Almost all sealers used in pitch pans will crack eventually due to loss of plasticizer or aging. If the penetration is not stabilized, vibration or movement of the penetration can cause the sealant to crack around the penetration. If a penetration is not thoroughly cleaned of asphalt before installing pourable sealers, the sealer will not adhere to the penetration.

Other types of penetration flashings also can fail. Concrete curbs filled with sealer will crack if not fully supported underneath. Metal pans eventually rust and lose adhesion to the sealer. Rubber and plastic boots will deteriorate with ultraviolet radiation exposure. The sealant used at metal penetration flashings eventually deteriorates with exposure and may not seal to the penetration if the penetration has not been properly cleaned before installation. The penetration flashing may also leak if the wrong diameter flashing is used or the cover is not correctly installed.

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Cooling the Planet with Cool Roofs

Cool roofs (like those from Conklin) and other reflective surfaces could help mitigate global warming by physically cooling the planet. Increasing the reflectivity of roofs and pavements in all North American cities with populations greater than 1 million would achieve a one-time offset of 57 gigatons of carbon dioxide emissions — double the worldwide carbon dioxide emissions total of 2006.

"Cool roofs are one of the quickest and lowest cost ways we can reduce our global carbon emissions and begin the hard work of slowing climate change," says U.S. Secretary of Energy Steven Chu.

The advantage of reflective surfaces as a method of physically cooling the planet is that it's actually a double-barreled attack. By reducing the temperature in urban areas, less air conditioning energy is used, and therefore fewer carbon dioxide emissions are produced. In addition, because cool surfaces reflect the sun's energy back to space, the actual temperature of the planet is lowered.

A Lawrence Berkeley National Laboratory study found that raising the Earth's average reflectance by 0.3% would result in an average temperature decrease of 0.01 degrees Celsius. That may sound like a modest temperature change, but it's also a relatively modest reflectance change. And, as Andre O. Desjarlais says, "every little bit helps."

The Cool Roofs Roadmap lays out plans to work with India and China on research to try to determine how cool surfaces can not only cool the planet, but also reduce pollution.

"If we do the research, and if the research shows what we suspect in terms of urban heat island mitigation and global cooling, policy can be based on this research," says P. Marc LaFrance.

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