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RESNET Issues Interpretation on Defining External Shading and Shading in HERS ANSI Standard

Jun 18, 2015

There is a concern that currently RESNET accredited HERS software programs are able to account for shading from adjacent buildings, trees and shrubs in the rating process. In some interpretations, adjacent shading might be included only in the analysis of the Rated Home energy usage and not in the analysis of the Reference Home energy usage.  The impact of such an interpretation on the HERS index can be substantial.  Adjacent objects are not part of the Rated Home design.  Characterizing the relative location and physical attributes of these objects (or a simplified representation of the shading from these objects) is highly subjective and can lead to inconsistency in the rating process.

To resolve this issue, the RESNET Standards Development Committee’s Calculations Subcommittee has adopted a standard interpretation defining ANSI/RESNET 301-2014’s Table 4.2.2(1), Glazing External Shading and Table 4.4.2(1), 6. Windows Shading.  The adopted interpretation is:

The terms External Shading and Shading refer only to permanent, fixed shading devices attached to the building such as fins and overhangs, and that window screens, movable awnings, roller shades, and shade from adjacent buildings, trees and shrubs shall not be included.

The interpretation goes into effect on July 13, 2015.