Retro-Commissioning | Cool Roofs
People who live in tropical climates usually wear light-colored or white clothing to help keep themselves cool. They know that light colors reflect heat and sunlight; whereas dark colors absorb heat and light. Buildings are similar to people. If you have a dark-colored roof, your building will be hotter than if it had a light-colored roof.
Cool Roofs are roofs consisting of materials that very effectively reflect the sun’s energy from the roof surface. Cool materials for low-slope roofs are mainly bright white in color, although non-white colors are starting to become available for sloped roof applications. Cool Roofs must also have high emissivity, allowing them to emit infrared energy. Unfortunately bare metals and metallic coatings tend to have low emissivity and are not considered cool materials.
Cool roofs can reduce the roof surface temperature by up to 100 degrees Fahrenheit, thereby reducing the heat transferred into the building below. This helps to reduce energy costs (by keeping attics and ducts cooler), improve occupant comfort, cut maintenance costs, increase the life cycle of the roof, and reduce urban heat islands along with associated smog.
Some benefits of Cool Roofs:
- Save on annual electricity bills by reducing summer air conditioning costs.
- Save peak electricity demand costs if you have time-of-use metering.
- Reduce roof maintenance and replacement expenses by extending roof life.
- Increase indoor comfort in summer by reduction of infrared conversion from visible light.
- Reduce the “heat island effect” in cities and suburbs.
- Reduce air pollution and smog formation.
- Reduce roofing waste added to landfills.
- Help builders and building managers meet California’s Title 24 Energy Efficiency Building Standards.
These pictures show hand-held temperature readings from before and after a cool roof treatment.
Roof before treatment, thermometer reads 178-degree Fahrenheit
at the roof surface on a hot summer afternoon.
After a cool roof was installed, there was a dramatic decrease in roof air temperature.