Specify “Green” and Realize Big Life-Cycle Savings with Cool Roofing
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By Drew Ballensky
Rising energy costs and recent regulations – such as California’s Title 24 Building Code and Section 303 of the Chicago Energy Code – have made cool roofing a white-hot topic again among architects, specifying contractors, building owners, and government officials responsible for building codes and the environment. In fact, cool roofing is considered by many scientists and government officials to be an effective means of addressing critical national energy efficiency and environmental challenges.
Their proven effectiveness at reducing both energy consumption and air pollution have made cool roofing systems popular among architects and contractors, who also specify white, reflective roofing for their aesthetic advantages. However, there is one important aspect of cool roofing that is often overlooked – their significant potential life-cycle cost benefits. Given the immediacy of rising energy costs and regulatory momentum, this is a good time to review cool roofing dynamics and their long-term, life-cycle cost benefits.
Cool Roofing Dynamics.
Understanding the cost benefits of cool roofing systems begins with a basic understanding of their dynamics. Cool roofing is a relatively new trend, but mankind has understood for centuries that white or light-colored surfaces are cooler than dark surfaces. Recent studies by Oak Ridge National Laboratory (ORNL) have demonstrated different levels of
solar reflectance and infrared emittance among various materials:
Reflectance, also known as albedo or reflectivity, is the percentage of solar energy reflected by a surface. The higher the percentage of reflectance, the more heat energy will be reflected from the surface. Generally, white or light-colored surfaces have the greatest reflectance.
Emittance, or emissivity, is the amount of heat energy a material can absorb and then shed in the form of infrared radiation. Materials with low emittance tend to heat up more easily because they collect and trap heat. It is interesting that while many black materials have very low reflectance, they can exhibit very high
Lawrence Berkeley National Laboratories (LBNL) has led related research into the dynamics of urban heat islands, or UHIs – even small cities are typically three to ten degrees warmer than nearby suburbs or countryside. Using infrared photographs from outer space, LBNL has confirmed that most large American cities suffer from the heat island effect. The UHI chain of cause and effect is clear: As temperatures increase, more electric power is needed for air conditioning, and more fossil fuel is consumed. This causes higher levels of air pollution. LBNL has established that the probability of smog creation rises 5 percent for each one-half degree increase above 70°F. While reduced vegetation accounts for the largest percentage of the UHI at 56 percent, dark roofing surfaces run a strong second at 38 percent.
What is Cool Roofing?
Although there is no industry-wide definition of a cool roof per se, the EPA’s ENERGY STAR ROOF® Products Program has established a minimum standard, requiring that low-slope roof products have an initial reflectance of at least 65 percent and a reflectance of at least 50 percent after three years of weathering. ENERGY STAR ratings can be found on their web site,
State and local regulations are another means of defining what constitutes a cool roof. Under the Chicago Energy Code, lowslope (relatively flat) commercial roofs installed after April 1, 2003 must have a minimum reflectance of 25 percent; after December 31, 2008, low-slope roofs must meet or exceed the criteria to qualify for an Energy Star label (currently set at 65% initial and 50% weathered reflectivity). California’s Title 24 Building Code is a little more aggressive. Effective October 2005, Title 24 mandates that, in most cases, new and replacement commercial roofs have a minimum initial thermal emittance of 75 percent, and a minimum initial solar reflectance of 70 percent.
The Cool Roof Rating Council (CRRC) was established in 1998 as a non-profit association to implement and promote fair, accurate performance ratings for solar reflectance and emittance from roof surfaces. All tests are performed by accredited, independent laboratories following established American Society of Testing Materials (ASTM) protocols. Performance data for more than 100 products from 30 manufacturers can be found on their web site,
Environmental and Cost Benefits of Cool Roofing.
High-performance cool roofing systems have several related environmental advantages:
Cool roofs reduce the UHI effect by reducing the amount of dark, solar energy-absorbing surfaces.
Reducing the UHI effect results in lower urban temperatures, less air pollution, and less energy demand for air conditioning.
Some single-ply cool roofing systems with full warranties can be installed directly over existing roofs, eliminating the need for tearing off the existing roof and placing the waste in landfills.
Many, but not all, of the cost benefits of good cool roofing systems are related to their environmental advantages: Cool roofs can reduce annual air conditioning consumption by 10 percent to 40 percent, depending on location, building design, climate, and other factors.
Reduced air conditioning demands have enabled many buildings to downsize their air conditioning equipment considerably.
Air conditioning units will also run less, which reduces wear and maintenance on the units.
Reflective membranes typically last longer because they slow down the rate of chemical reactions, or degradation. The rate of these reactions generally doubles for every temperature increase of 18°F. Clearly, highly reflective roof membranes are cooler (Fig. 1), and will last longer than dark membranes with similar chemical compositions. Longer service reduces the cost of a roof over time, and also reduces the amount of waste going into landfills.
The cost benefits of cool roofing are greatest in southern climates, but significant advantages can be realized in most North American cities (Fig. 2). Indoor comfort can be improved dramatically in buildings that are not climate-controlled. Cool roofs have been shown to reduce interior temperatures by 15 to 20 degrees on hot days.
Life-Cycle Cost Benefits
We hear more and more about the life-cycle costs of building materials and systems, driven in part by environmental impact considerations. Unlike installation costs, which are relatively easy to calculate, life-cycle costing must estimate future considerations such as longevity, maintenance and repair, and the longterm impact on overall facility operations. Life-cycle cost estimates are not as precise as installation cost estimates because variables can change, but life-cycle cost estimates can serve as a useful guide to the value of building system choices over time.
This is especially true with cool roofing, where energy savings alone can make a big difference in the 20-year cost of a roof. About a year ago – before the most recent energy price increases – we asked several Midwest roofing contractors to help us prepare a hypothetical, 20-year life-cycle cost comparison for a fullywarranted, 50,000 square-foot re-roof in the Midwest.
For the cool roof, we selected a PVC single-ply system, the cool roof with the longest track record (dating back to the 1960s). For the traditional black roof, we took contractor estimates for the two most popular systems – built-up asphalt roofs and EPDM single-plies – then averaged them. For energy savings, we used the EPA ENERGY STAR Roof Products Program cool roof energy savings calculator (available online at
http://roofcalc.cadmusdev.com) and projected out 20 years.
Although far from perfect, this hypothetical life-cycle cost comparison clearly demonstrates the impact that a cool roof can have over time. The total Installed costs – the cost of the roof product, installation, tear-off and disposal – are pretty close: $142,500 for the traditional black system; $133,000 for the white PVC cool roof. Estimated maintenance and repair could vary considerably, but these costs are relatively low compared with other variables.
The biggest difference is clearly in energy savings, where the cool roofing system saves the building owner an estimated $4,200 a year. Based on our experience, this is actually a conservative estimate, especially considering the energy price increases we have experienced during the last year or so.
Cool Roofing is a Win-Win
While many “green” building products have cost or performance tradeoffs, contractors, architects and building owners have discovered that there really is no downside to choosing the best cool roofing systems in terms of life-cycle cost, durability, maintenance, or overall product performance. Energy savings alone can reduce the cost of a cool roof by a factor of two or three compared with traditional, nonreflective roofing systems.
About the Author, Drew Ballensky is the general manager of Duro-Last Roofing Inc.’s Iowa plant and spokesman for the
Duro-Last® Cool Zone™ roofing system. He can be contacted at 877-556-6700.