There are different cool roof standards for commercial low slope roofs and residential steep slope roofs.
Low slope cool roof treatment sri.
Minimum solar reflectance index value by roof slope.
Install compliant cool roof material that is listed in the cool roof rating council crrc rated product directory 0 63 aged solar reflectance 0 75 thermal emittance or an sri of 75.
Minimum sri values of 78 and 29 for low and steep sloped cool roofs respectivelyiii.
Wrapping it all up.
Commercial cool roof options include bright white membranes and white coatings.
Low slope roofs require an initial sr value of 0 65 or higher and 0 50 or greater after three year.
Painting a metal roof can increase its solar reflectance and thermal emittance allowing it to achieve cool roof status.
If aged sri is not available the roofing material shall have an initial sri equal to or greater than the values in table 1.
The ages solar reflectance and thermal emittance requirements will vary depending on the slope of the roof climate zone and the density of the roofing product.
Department of energy doe has decided to implement cool roofs on all its buildings whenever practicable3.
Low slope roofs face the sun on a more consistent and extended period of time than steep slope roofs because they re flatter which is why the reflectance and sri values must be higher to withstand the longer duration of heat from the sun.
Low slope roof less than 2 12 slope check applicable box below.
Emissivity is a material s ability to release absorbed energy.
3 yr aged solar reflectance min.
Tapered insulation is the most common method for creating a slope on a low slope roof but frustratingly neither code addresses compliance for tapered systems.
Cool roof requirements for residential and non residential now apply to low slope and steep slope roofs.
Roof area covered by building integrated photovoltaic panels and solar thermal panels.
Sri low slope1 13 15 0 63 0 75 75 steep slope1 10 thru 15 0 20 0 75 16 1 low slope rise to run ratio of 2 12 lower than 9 5 degrees steep slope rise to run ratio 2 12 9 5 degrees or more table 1 residential cool roof.
Or this sri value roof slope climate zone min.
In addition the common belief that an average r value is just as good as the code requirements is just that a common belief not a fact.
How they can be made cool.
Use roofing materials that have an sri equal to or greater than the values in table 1.
Residential roofing options include asphalt shingles metal clay tiles and concrete tiles.
The solar reflectance index is used for compliance with leed requirements and is calculated according to astm e 1980 using values for reflectance and emissivity.
