High Albedo Roof Requirements

Requirements option 1.

High albedo roof requirements.

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. There are two properties that are used to measure the effects of cool roofs. Built up roofs consist of a base sheet fabric reinforcement layers and usually a dark protective. Install high albedo and vegetated roof surfaces that in combination meet the.

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. Install a vegetated roof for at least 50 of the roof area. Reformulate or coat black membranes to make them reflective. Solar reflectance also known as albedo is the ability to reflect sunlight.

As expected high albedo roofs save summer cooling energy but also increase the required winter heating energy. 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. 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. 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. Or option 3. 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. 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.

Thermal emittance is the ability to emit absorbed heat. Natural weathering can have detrimental effects on a roof s ability to maintain high reflectance and watertightness. There are different cool roof standards for commercial low slope roofs and residential steep slope roofs. It is also expressed.

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.