Steep slope: Metal – $1.80-$3.75 per sq ft; Tiles – $0.60-$6.00 per sq ft
Applications: Can be installed in retrofits or in new construction.
Service Life: Extensive (30 years to lifetime). Can extend roof life due to lower temperatures.
Cool roofs are constructed with highly reflective and emissive materials, usually in the form of membranes, coatings, and tiles. Cool roofing materials can have solar reflectance of over 65%, compared to 5-15% for traditional roofing materials. As a result, cool roofs tend to stay within 10-20⁰F of ambient air temperatures in the summer, while conventional roofs can be 55-85⁰F hotter than ambient air temperatures. A simulation of New York City found that use of cool roofing on 50% of available roof surfaces would reduce city-wide temperatures by 0.3⁰F.
Cool roofs are typically categorized as low slope or steep slope, which use different roofing materials. Low slope cool roofs are defined as having no more than a 2:12 pitch. Low slope cool roofs use single-ply membranes or cementitious and elastomeric coatings to increase solar reflectance and thermal emittance. Cool roof retrofits are often considered when existing roofs near the end of their service life. Cool roof coatings have typically been applied to existing roofs that only need moderate repairs, while membranes are often used for roofs needing more extensive repairs. Steep slope cool roofs typically use specially-colored tiles with higher solar reflectance or metal roofing to reduce solar heat gain.
While cool roofs reduce cooling energy use in the summer, they can also reduce the amount of solar heat in the winter that could be used to warm the building. As a result, summer energy savings may be partially offset by increased heating costs. In most climates, this offset does not typically exceed the summer energy savings. Building owners should consult tools like the Oak Ridge National Laboratory’s Roof Savings Calculator to determine if cool roofing is a viable investment.
- Reduces building summer cooling costs through increased solar reflectance.
- Reduced peak temperatures from cool roofing will increase the service life of the roof and reduce lifetime maintenance costs.
- Cheaper than green roofs while providing similar cooling benefits.
- Reduces smog formation.
- Lighter than a green roof, reduced weight.
- Can be installed on any roof, including sloped and curved roofs that cannot accommodate green roofing.
- Reduced solar reflectance results in increased heating costs in winter. Ultimate net benefit will vary based on geographic region.
- Creates glare in other buildings, reflected light can raise cooling costs in surrounding buildings.
- Requires regular cleaning to maintain reflectivity. Solar reflectance decreases with wear.
- Traps more heat than a green roof.
- Fewer ecological benefits than a green roof.
Regulatory Impacts and Requirements
Financing Options, Incentives, And Rebates
- Green and cool roofing are part of the City of Boston’s Climate Action Plan, and policies and programs to support cool roofing may appear in Boston in the near to medium term
- A list of rebates and loans from the Cool Roof Rating Council can be found here: http://coolroofs.org/resources/rebates-and-codes
- State Energy Program – federal funds given to states
SAMPLE OF SUPPLIERS
*indicates Boston Area supplier
Photo credit: Wal-mart, CC by 2.0 [https://creativecommons.org/licenses/by/2.0/legalcode], Flickr