B2.6 Cool roofs *
Create an incentive program for the installation of reflective roofs on commercial buildings to reduce building energy consumption and the urban heat island effect.
Cool roofs
HB 1114, which was adopted in 2021, includes mitigation of urban heat island effects through cool roof programs as an activity that private utilities like PSE can include in their conservation programs, which earn an incentive rate of return on the investments.
New York City estimates that cool rooftops can reduce internal building temperatures there by up to 30%, and that coating 2,500 square feet of roof can reduce the city’s carbon footprint by 1 ton of CO2. (They extend the life of the rooftop and the building’s cooling equipment, and contribute to reducing the city’s heat island effect, as well as reducing energy use and associated emissions.) A city program in which volunteers installed cool roofs has now converted to a workforce training program which provides free or low-cost cool roofs to non-profits and a number of other kinds of buildings like schools and museums. (The City also provides the labor, technical support and additional materials like brushes for coating a roof to any other New York City building if the owner pays for the actual reflective coating liquid.) Its goal is to coat a million square feet of roof a year.
Denver’s Commercial Energy Program requires commercial buildings over 25,000 sq. ft. to install a cool roof when they replace the current roof, and to choose one of five additional compliance options – green roof/green space equal to 18% of the roof area; on-site solar equal to 42% of the roof area or renewable equivalent; various high efficiency certifications; an energy efficiency program; or a $50/sq. ft. payment to the Green Building Fund in lieu of the green roof coverage.
The Department of Energy has an overview of the issues.
The Cool Roof Rating Council has a webpage that tracks cool roof code requirements, rebates, and incentive programs in cities around the country.
Green roofs
(These are almost always installed on new buildings, not existing ones. It’s a lot of load on the roof, and it has to be surfaced and sealed to deal with a lot of water.)
Philadelphia has a number of substantial incentive programs for green roofs, focused on improving its water quality.
Toronto also has major stormwater problems, and has an incentive program for green roofs and cool roofs on homes and buildings, and a graduated green roof requirement for new development or additions that are greater than 2,000 m² in gross floor area.
Denver passed a green roofs initiative, which they soon decided needed to be reworked into a cool roofs initiative.
Our local weather may make green roofs harder to maintain during long dry summers, and less effective in reducing stormwater runoff when they’re saturated during the winter. Seattle did a study of the actual performance of a few green roofs there in controlling stormwater flows; their performance varied a lot, but they were all significantly better at slowing peak flows than at reducing total runoff. (Evergreen has had ongoing issues with leaks and with maintaining the prizewinning green roofs on the Seminar II building.) The General Services Administration maintains about 2.2 million square feet of green roofs on over eighty buildings, including three in Portland and one in Seattle.
Michigan State University’s green roof research website includes an overview of the research on their benefits.