What are Cool Roofs?
A cool roof is a roofing system with a membrane or coating that is light in color such as white, light gray, and tan. Unlike a conventional dark-colored roof, white roof systems reflect a large percentage of sunlight and quickly emit any heat absorbed into the roofing membrane or coating. A lower roof temperature means less heat entering the building through the roof membrane or coating, which reduces building cooling costs and extends roof service life. Cool roofing is a proven strategy to reduce building energy costs, greenhouse gas emissions, and the urban heat island effect.
How do Cool Roofs Work?
A white color roof works similarly to wearing light-colored clothing on a sunny day. White roofs are made with solar-reflective materials that absorb less sunlight than a conventional dark roof. Less heat-absorption means a lower surface temperature. This directly reduces heat gain through the roof and air-conditioning demand and leads to significant energy savings. In
one case study, a 100,000 sq. ft building in Austin, TX with a cool roof saved 14% on peak hour cooling costs, which resulted in annual savings of more than $10,000.
A number of studies by scientists at Lawrence Berkeley National Laboratory, Department of Energy, the National Center for Atmospheric Research in America (NCAR), and the University of Perugia in Italy all support the energy and carbon benefits of cool roofing products and systems for low-sloped roofs and steep-sloped roofs.
What are Cool Roofs Made of?
Cool roof membranes or coatings can be made from various materials such as PVC, TPO, EPDM, etc. They contain special pigments that reflect sunlight and can protect the roof membrane from UV.
What are the Benefits of Cool Roofs?
Cool roofs can reduce energy bills by diminishing A/C needs, improving indoor comfort for spaces that do not have A/C, and decreasing roof operating temperature, which may extend roof service life. They also boast a myriad of environmental benefits such as reduced local air temperature, which improves air quality and decreases smog, reduced peak electric power demand which leads to fewer power outages, reduced power plant emissions by reducing the cooling energy use in buildings, and reduced heat trapping in the atmosphere by reflecting more sunlight back into space, slowing climate change.
How Does a Cool Roof Compare to Other Roof Types?
A white roof versus a black roof ( or any dark-colored roof) such as EPDM rubber, Modified Bitumen or multi-layered asphalt sheets (Built-up) is the optimal choice for both the environment and the wallet due to the energy savings and its reduction of the urban heat island effect and other environmental factors.
Another roofing system commonly referred to as a cool roof is the Green “Vegetated” Roof or Garden Roof. Green roofs, like white roofs, can also help lessen the urban heat island effect, improve air quality, and reduce a building’s demand for energy usage. Unfortunately, green roofs are typically more expensive and heavier. Sarnabrite and Sika SolaRoofs
Skylights and solar can also be considered in any roofing-related energy strategy.
What is the Urban Heat Island Effect?
Anyone who lives or works in the city knows well that it’s hotter in the concrete jungle than in surrounding rural areas. The urban heat island effect (UHIE) is a phenomenon where a city experiences significantly warmer temperatures than nearby rural areas. Some of the major factors contributing to the UHIE are the large volume of dark-colored roofs and pavements, along with fewer trees and shrubs to shade surfaces.
Dark roofs collectively absorb significant amounts of the energy radiating from the sun, increasing the overall local temperature. These higher temperatures increase smog formation, which is compounded by the increased greenhouse gas emissions resulting from the power generation to further condition, or cool, living and working spaces to make up for the higher urban temperatures.
Dark-colored, hot roof surfaces are being targeted to minimize the heat island effect because they are unnecessary sources of heat that contribute to elevated air temperatures and increased demands on air conditioning which, in turn, leads to smog formation, higher energy bills, and heat-related illnesses.
Cool roofs are economical and ecological. The Lawrence Berkeley National Laboratory predicts that installing cool roofs, cool pavements, and trees over about 30% of the Los Angeles basin could reduce the local ambient temperature by as much as 5 degrees Fahrenheit. It is estimated that this would reduce smog by 10%. As a result of the lower ambient temperature, annual building cooling energy savings would be about 50% greater than expected for the roof alone. With less future A/C costs, the effect is significant reductions in greenhouse gases such as CO2.3
Are Cool Roofs Only for Hot Climates?
One myth that has been disproven over time is that cool roofs only make sense in hot climates but not in cool climates. The incorrect assumption was that the absorption of heat from the sun in cooler temperatures would help warm the building in the winter. However, studies have shown that, even in cool climates, cool roofs can help a building owner save energy and money on an annualized basis compared to a black top.
Studies have shown that a cool or white roof membrane can reduce average summertime air conditioning peak demand (1-4 pm) by 14% and the total daily air conditioning energy usage by 11%. However, peak demand is not just a warm climate problem. Oak Ridge National Laboratories examined the seasonal variation in peak air conditioning demand for various climates across North America. Their findings suggest that, even though base cooling demand may be higher in hot climates when compared to cooler climates, the ratio of monthly peak demand to annual peak demand is very similar across all climates.
Read more on cool roofs in cold climates
How Much Energy Does a Cool Roof Save?
The energy savings from installing a white roof can vary depending on where your uilding is located, the traditional climate and how much energy your building currently uses. White roofs are economic and ecological. The Lawrence Berkeley National Laboratory predicts that installing cool roofs, cool pavements, and trees over about 30% of the Los Angeles basin could reduce the local ambient temperature by as much as 5 degrees Fahrenheit. Estimates predict that this could reduce smog by 10%. As a result of the lower ambient temperature, annual building cooling energy savings would be about 50% greater than expected for the roof alone. With lower future A/C costs, the effect is significant reductions in greenhouse gases such as CO2.
What is the Cool Roof Rating Council?
The Cool Roof Rating Council (CRRC) was formed in 1998 to develop the most accurate methods for evaluating the solar reflectance and thermal emittance of roofing products and share that information with the public. The CRRC has collected solar reflectance and thermal emittance data for more than 2,000 products and has set standards for cool roof products based on reflectance, emittance, and solar reflectance index (SRI).
Solar reflectance measures the fraction of solar energy that a roof reflects. Thermal emittance refers to the ability of a roof surface to radiate away the heat it absorbs. The solar reflectance index (SRI) is another metric for comparing the “coolness” of a roof membrane or coating, which considers both the solar reflectance and thermal emittance.
Reflective light-colored roofs, such as Sika Sarnafil’s EnergySmart Roof, are being recommended by both the scientific and environmental communities to help mitigate temperature increases in buildings and surrounding areas and improve air quality.
Are Cool Roof Benefits Reduced When the Roof Becomes Dirty?
No. Most cool roofs do not lose significant cooling benefits when subject to various forms of soiling relative to darker roofs. All outdoor surfaces are subject to getting dirty. However, a review of CRRC's low slope products database shows that 90% of these samples still retain a significant amount of their initial reflectivity after three years. Studies have shown that roof cleaning can restore practically 100% of initial reflectivity for many products, should an owner maintain that level.
Will Wetting a Roof Cool a House or Building?
If you're wondering how to cool a roof in the summer, wetting a dark-colored roof might cool a house or building temporarily and on a small scale (it also adds costs to your water bill). A cool or white roof, on the other hand, is a long-term solution with no additional steps to take.
How Much Do Cool Roofs Cost?
Typically, cool roofs cost the same or even less than darker membrane alternatives (except a green vegetative roof).
Energy-cost savings achieved will depend on climate, amount of roof insulation, energy prices, and building use. It is important to consider that, along with energy savings, some utilities and agencies offer rebates and incentives for cool roofs. HVAC equipment savings may also be achieved when a cool roof reduces peak cooling loads enough to reduce the air condition capacity needed. The lower rooftop temperature may also extend the membrane's service life.
Are Cool Roofs Worth it?
Yes. Dark, heat-absorbing roofs become extremely hot and are unnecessary sources of heat that contribute to elevated temperatures and increase a building's cooling energy needs. Increasing air temperatures translate into poorer air quality. Highly reflective cool roofs diminish this condition and have been identified as an environmentally preferable roofing solution. They provide economic, energy efficiency, durability, and environmental benefits.
Should I Install a Cool Roof? What Colors are Cool Roofs?
If you plan a new building or replace or restore an existing roof, a cool roof system should be viewed as an energy-efficient, cost-effective, and long-term solution. If you’re wondering whether installing a cool roof is the right decision for you, consider the cost-benefit analysis. White roof surfaces have been proven to reduce the energy required to maintain comfort in an air-conditioned building by decreasing heat flow through the building envelope. Note that while white roof materials tend to be very good solar reflectors, colored roofing materials can also be made to reflect more sunlight. Sika Sarnafil's EnergySmart Roof features options for a White, Tan, Reflective Gray, or Patina Green reflective surface. They also meet and/or exceed the criteria from the Cool Roof Rating Council (CRRC) for a roofing membrane to qualify as a cool roof.
Using a highly reflective EnergySmart roofing membrane from Sika Sarnafil can save significant amounts of energy, depending on the location of the building, and that means financial savings. For example, if 80% of all commercial buildings in the U.S. had cool roofs, it has been estimated that there would be approximately $735 million in overall energy savings. Ultimately, cool roof products exist for virtually every kind of roof. Cool roofing systems like the EnergySmart Roof can save money, improve occupant comfort, increase a roof’s longevity, and reliably protect a building and its contents, meaning the benefits are well worth considering.
Sika Cool Roof Systems – What Makes a Good Product?
Our extensive product portfolio of roofing and waterproofing membranes for low and steep sloped commercial roofs includes solutions for virtually any cool roof application.
|Requirements||Do Sika Sarnafil’s Systems meet the requirements?|
|High initial Solar Reflectance Index (SRI) values||✓|
|High reflectance value after 3 year exposure||✓|
|The benefits of cool roofs (significantly reduced energy consumption) is maintained throughout the service life||✓|
|Meets LEED requirements for white reflective roofing||✓|
|Lower surface temperatures increase life expectancy||✓|
|Environmental Product Declarations (EPD) available||✓|
Learn more about cool roofs in this webinar.
Want More Reading Material?
1. CFFA Chemical Fabrics and Film Association Vinyl Roofing Division. Cool Roofing Myths.
2. CFFA Chemical Fabrics and Film Association Vinyl Roofing Division. Cool Roofing Myths.
3. Graveline, Stanley, Sika Corporation Roofing. The Heat Over Cool Roofs: Setting the Record Straight on Reflective Roofing.
4. Sika Corporation – Roofing. How Demand Charges Are Increasing Your Energy Bill.
5. CFFA Chemical Fabrics and Film Association Vinyl Roofing Division. Cool Roofing Myths.
6. Graveline, Stanley, Chemical Fabrics and Film Association. Cool Roofs Not Just For the Sun Belt. (Commercial Building Products, January/February 2014).