Cool Roofs offer multiple benefits
A “cool roof” reflects more sunlight and retains less heat than a warm roof. During summer a cool roof can be more than 50°F cooler than a warm roof. Solar reflectance (SR) and thermal emittance (TE) are the characteristics that determine “coolness”. Cool roofs are available in a variety of colors and materials. Material options include a highly reflective coating, a sheet covering, or highly reflective tiles or shingles.
Benefits of Cool Roofs
- Cool roofs save money through HVAC energy efficiencies, incentives, and extended roof lifetime. Estimate energy savings by using DOE Cool Flat Roof Calculator.
- Improved indoor comfort for spaces that are not air conditioned.
- Reduced roof temperature extends roof service life and reduces damage to roof membrane systems.
- Reduce local air temperatures [urban heat island effect]
- Lower peak electricity demand helps prevent power outages.
- Reduced power plant emissions.
- Cool metal roofing can qualify for 1 point within LEED-NC 2009, Sustainable Sites Credit 7.2, Heat Island Effect by using materials that meet minimum SR levels for low sloped roofs and for steep sloped roofs. The Lawrence Berkeley National Laboratory SRI Calculator is available online. [Obtain SR and TE percentages for cool metal roofing products from the Cool Roof Rating Council or ENERGY STAR to enter into calculator.]
Low and Steep Sloped Roofs Can Be Made Cool
- Single-ply membranes: Reformulate or coat black membranes to make them reflective.
- Built-up roofs: The surface layer has cool options:
- Substitute reflective marble chips or gray slag for dark gravel in a flood coat of asphalt
- Use reflective mineral granules or a factory-applied coating on a mineral surfaced sheet
- Apply a cool coating directly on top of a dark asphaltic emulsion coating.
- Modified bitumen sheet membranes: Pre-coat with a cool roof coating at the factory.
- Spray polyurethane foam roofs: Their reflective protective coatings offer cool roof performance.
- Metal roofs: Unpainted metals are good solar reflectors. Painting a metal roof can further increase its solar reflectance and thermal emittance, allowing it to achieve cool roof status. Cool pigments allow metal roofing products to be EnergyStar rated in dark colors.
- Shingle roofs: Shingles with specially coated granules or coated at the factory for cool SR.
- Tile roofs: Surface treatments can transform tiles with low SR into cool roof tiles.
References: US DOE Article on Cool Roofs Cool Roof Rating Council Article On Cool Roofs
- Category: Tech Tips, Energy Efficiency