When a roof can deliver high solar reflectance or albedo and thermal emittance values it is known as a cool roof.
Green roofs emittance and albedo.
They may also have a high thermal emittance value.
Albedo or solar reflectance is a measure of a material s ability to reflect sunlight including the visible infrared and ultraviolet wavelengths on a scale of 0 to 1 an albedo of 0 0 indicates that the surface absorbs all solar radiation and an albedo of 1 0 represents total reflectivity.
Albedo is a unitless measure with possible values ranging from 0 to 1.
A vinyl roof can reflect three quarters of the sun s rays usually far more and emit 70 or more percent of the solar radiation absorbed by the building envelope.
Albedo albedo or solar reflectance is a measure of a material s ability to reflect sunlight including the visible infrared and ultraviolet wavelengths on a scale of 0 to 1.
An albedo of 0 0 indicates that the surface absorbs all solar radiation and an albedo of 1 0 represents total reflectivity.
An energy calculator for green roofs.
Green roof energy series part 6.
Sustainable roofing glossary albedo.
A standard white reflectance 0 08 and emittance 0 90 is 100.
They can also reduce the urban heat island effect.
This is due to the nature of the roof itself.
The solar reflectance of green roofs varies depending on the plant types generally 0 3 0 5.
Flat or low pitch roofs in particular need to meet a reflectance value of 0 65 and an emittance value of 0 50.
Mindful that reflectance and albedo can be different a combination of high albedo and high emittance resists solar heat gain most effectively.
Cool roofs use roofing materials that are highly reflective also called high albedo roofs of the sun s radiant heat.
Cool roofs are able to reduce heat gain in buildings due to the high solar reflective index.
Emittance is a measure of how much of the absorbed radiant energy is given off into the atmosphere keeping the surface cooler as a result.
However emittance also matters because the higher the emittance the more readily the roof surface will radiate long wave ir heat to the sky.
Green roofs provide a thermal mass layer which helps reduce the flow of heat into a building.
Cool roofs are pretty cool but whether or not they save as much energy as a green roof requires as usual a closer look at a a cool roof and b a given green roof design.
Finally keep in mind that the style of your roof will affect the necessary reflectance and emittance values your new roof should meet.
Peck is the founder and president of green roofs for.
Green roofs may not reflect as much as a cool roof but do have other benefits such as evapotranspiration which cools the plants and the immediate area around the plants aiding in lowering rooftop.
Although cool roofing is one of the most significant green technologies today it is not a new concept.
