High Albedo Roof Requirements

In climate zones 1 2 and 3 ashrae 90 1 s prescriptive method also allows for reducing a roof assembly s minimum required r value if the roof assembly s surface has a high albedo high reflectivity and emittance. Use roofing materials having a solar reflectance index sri equal to or greater than the values in the table below for a minimum of 75 of the roof surface. While conventional roofing materials warm up by an average 0 055 degrees c w m sup 2 sup the high albedo surfaces warm up by an average 0 015 degrees c w m sup 2 sup p.

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High albedo roof requirements.

Requirements option 1. Install high albedo and vegetated roof surfaces that in combination meet the. It is expressed either as a decimal fraction or a percentage. How they can be made cool.

There are different cool roof standards for commercial low slope roofs and residential steep slope roofs. Thermal emittance is the ability to emit absorbed heat. This list includes low slope roof products with an initial reflectance of at least 65 percent and a reflectance of at least 50 percent after three years of weathering. Natural weathering can have detrimental effects on a roof s ability to maintain high reflectance and watertightness.

Built up roofs consist of a base sheet fabric reinforcement layers and usually a dark protective. Or option 2. There are two properties that are used to measure the effects of cool roofs. Install a vegetated roof for at least 50 of the roof or install high albedo and vegetated roof in combination area of sri roof 0 75 area of veg roof 0 50 total roof area water efficiency.

Or option 3. As expected high albedo roofs save summer cooling energy but also increase the required winter heating energy. Install a vegetated roof for at least 50 of the roof area. In today s market a cool roof is defined by the reflectivity and emissivity requirements set by either title 24 from the california energy commission or by the energy star program.

Solar reflectance also known as albedo is the ability to reflect sunlight. Single ply membranes are pre fabricated sheets rolled onto the roof and attached with mechanical fasteners adhered with chemical adhesives or held in place with ballast gravel stones or pavers. It is also expressed. For example older buildings with lower roof insulation levels exhibit different savings for a high albedo roof than a new building with more roof insulation.

For a roof to meet albedo classifications it must emit no less than 65 measured as 65 on the solar reflectance value scale of radiant heat energy back into the atmosphere.

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