EnergyWise Roof Calculator Online is a Web-based application that allows roofing professionals to construct virtual roof assemblies to evaluate thermal efficiency and estimate energy costs via comparison of other roof assemblies (at ground level) absent other building envelope components. It also contains minimum thermal insulation requirements established by ASHRAE Standard 90.1-1999.
The information contained in this application is based in part on the provisions contained in the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Fundamentals Handbook and ASHRAE Standard 90.1-1999 (and 2001), "Energy Standard for Buildings Except Low-rise Residential Buildings."
With the 1999 version of ASHRAE 90.1, designers can demonstrate a roof assembly's compliance as part of the building envelope using the following methods:
Energy Cost Budget Method—Designers determine the "design energy cost" and illustrate it does not exceed the "energy cost budget."
Prescriptive Method—Building components (e.g., envelope, HVAC, power, lighting) have to meet the minimum requirements set forth in ASHRAE 90.1-1999. Under the prescriptive method, designers have two options:
Building Trade-off Option—The envelope performance factor of the "proposed" building is less than or equal to the envelope performance factor of the "budget" building.
Prescriptive Building Envelope Option—Roof assemblies shall meet a maximum U-factor and minimum insulation R-value as specified in Tables B-1 through B-26. This option only can be used if the skylight fenestration area doesn't exceed 5 percent of the gross roof area.
EnergyWise Roof Calculator Online is based on the Prescriptive Building Envelope Option. For more specific details and information, refer to ASHRAE Standard 90.1-1999. To purchase a copy of this standard, go to http://www.ashrae.org.
Because this application is intended to be a simplified guide specific to roof assemblies energy use, complex energy calculations, such as solar heat gain and exterior shading considerations, have intentionally not been included. For complex energy evaluation calculations, including evaluations of the entire building envelope, building usage, or changes to heating and air-conditioning equipment, consult the ASHRAE Fundamentals Handbook or an experienced mechanical engineer.
For a detailed financial analysis of the long-term costs and potential savings of an energy-efficient roof system, consult an experienced accountant.
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