Why Cool Roofs?
According to EPA, about $40 billion is spent annually in the US to air condition buildings — one-sixth of all electricity generated in a year! Cool roof products reduce the amount of air conditioning needed in buildings, and can reduce energy bills by up to 50 percent. There are many benefits to installing a cool roof from ElastiKote.
Downsize Cooling Equipment
A reflective roof can reduce peak cooling demand by 10-15%. As a result, the home or building owner may be able to purchase a smaller, more efficient, and less expensive cooling system.
Reduced energy demand means less burning of fossil fuels, which results in less pollution from power plants. Also, cool roof products help to reduce the “heat island effect,” in which dark, heat-absorbing buildings and paved areas make the air in urban areas hotter, and more smoggy.
Green Roof Ready
Over the last decade, green roofs have become a more common feature in urban environment. At the heart of any green roof is a roofing membrane; ElastiKote's unique properties make it an excellent choice for this role.
Resists Thermal Shock
Cool roof products maintain a more constant temperature and reduce thermal shock, which occurs when cool rain hits a hot roof, causing a sharp drop in temperature. During temperature changes, a roof expands and contracts, causing stress and degrading the roof.
Protects Against Water Pooling Damage
The collection of water on a roofing deck can cause structural failure not only due to the weight of the water, but also due to penetration of the deck by the water. The freeze/thaw cycle exacerbates the problem. ElastiKote has extremely low permeability, which reduces the risk of deck damage due to water permeation.
Reflection and Emittance
A high thermal emittance also plays a role, particularly in climates that are warm and sunny. Together, these properties help roofs to absorb less heat and stay up to 50-60°F (28-33°C) cooler than conventional materials during peak summer weather.1
Building owners and roofing contractors have used cool roofing products for more than 20 years on commercial, industrial, and residential buildings. They may be installed on low-slope roofs (such as the flat or gently sloping roofs typically found on commercial, industrial, and office buildings) or the steep-sloped roofs used in many residences and retail buildings.
Through the ENERGY STAR program, EPA and the Department of Energy (DOE) help consumers and other purchasers identify the most energy efficient roofing products.
Roofing materials with the ENERGY STAR label have met the minimum solar reflectance and reliability criteria. Based on 2006 data from more than 150 ENERGY STAR partners, shipments of cool roof products have grown to represent more than 25 percent of these manufacturers' commercial roof products and roughly 10 percent of their residential roof products.
Definition of Terms
Thermal Emissivity (emittance) is a measure of solar radiation (sun's rays) that is first absorbed and then radiated from a roof, expressed as a number between zero and one. The higher the value, the better the roof radiates heat. Any solar radiation that is not reflected (rejected outright, as with a mirror) is absorbed; this absorbed energy is then either radiated (i.e., emitted as infrared) or retained (adiabatic heat). In theory, the surface temperature of a material with 100% thermal emissivity would be equal to the ambient temperature (i.e., that of the surrounding air). Heat that is not released via the relatively efficient mode of infrared emittance is retained by the roof, which causes a buildup of heat. That heat is then released to the surrounding atmosphere via the less efficient (and slower) mode of conduction and convection.
Solar Reflectance Index (SRI) indicates the roof's ability to reject solar heat, and is essentially the combined value of reflectivity and emittance. It is defined such that a standard black is zero (reflectance 0.05, emittance 0.90) and a standard white is 1.00 (reflectance 0.80, emittance 0.90). Because of the way SRI is defined, very hot materials can have slightly negative SRI values, and very cool materials can have SRI values exceeding 1.00.
ASTM C1549 Standard Test Method for Determination of Solar Reflectance Near Ambient Temperature Using a Portable Solar Reflectometer (i.e., field testing).
Energy Star states that a "product shall be tested [for initial solar reflectance] using ASTM E 903 Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres (i.e., lab testing), but that a "product may also be tested using ASTM C 1549 (see above)1; "maintenance of solar reflectance" is field tested after three years using "either ATSM E 1918 Standard Test Method for Measuring Solar Reflectance of Horizontal and Low-Sloped Surfaces in the Field or ASTM C 1549.2
ASTM E 1980 Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Opaque Surfaces.
Green roofs are living plants installed on top of a conventional roof, and provide many benefits including:
- Reducing urban heat islands
- Extending the service life of a roof
- Cleaning the air
- Improving water quality
- Reducing sound reflection and transmission
- Using recycled materials
A green roof consists of these layers:
- Growing Medium
- Drainage, Aeration, Water Storage, and Root Barrier
- Roof Membrane
- Deck Structure
Due to it's low permeability, ease of application, and cost the Elastikote® roofing solution is ideal for use in Green Roof projects.
Urban Heat Islands
As urban areas develop, changes occur in their landscape. Buildings, roads and other infrastructure replace open land and vegetation. Surfaces that were once permeable and moist become impermeable and dry. These changes warm urban regions more than their rural surroundings, forming "islands" of higher temperatures in the landscape.
Source: EPA's Reducing Urban Heat Islands: Compendium of Strategies