High Albedo Roof Requirements

Or option 3.

High albedo roof requirements.

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. 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. How they can be made cool. 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. Or option 2. Built up roofs consist of a base sheet fabric reinforcement layers and usually a dark protective. It is also expressed.

Install a vegetated roof for at least 50 of the roof area. Requirements option 1. Install high albedo and vegetated roof surfaces that in combination meet the. Reformulate or coat black membranes to make them reflective.

Natural weathering can have detrimental effects on a roof s ability to maintain high reflectance and watertightness. There are two properties that are used to measure the effects of cool roofs. As expected high albedo roofs save summer cooling energy but also increase the required winter heating energy. There are different cool roof standards for commercial low slope roofs and residential steep slope roofs.

Solar reflectance also known as albedo is the ability to reflect sunlight. 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. 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 expressed either as a decimal fraction or a percentage.

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.