Code have been updated to the 2003 International Energy Conservation Code (IECC), because the corresponding U-values are identical and the IECC is more readily available (ICC 2003).
The Benchmark envelope specifications are as follows:
The same shape and size as the Prototype
The same area of surfaces bounding conditioned space as the Prototype with the exception of the attic, which shall be insulated at the attic floor and have a ventilation area of 1 ft2 per 300 ft2 ceiling area, regardless of the Prototype attic design
The same foundation type (slab, crawl space, or basement) as the Prototype.
The same basement wall construction type as the Prototype (e.g., masonry, wood frame, other)
No horizontal fenestration, defined as skylights, or light pipes oriented less than 45
degrees from a horizontal plane
Window area (AF), including framing, determined by Equation 1 for detached homes, by Equation 2 for attached homes, and by Equation 3 for multi-family homes (regardless of whether the hallways are interior or exterior).
AF = 0.18 × AFL,Liv
0.18 x AFL,Bsm
AF = (0.18 × AFL,Liv
0.18 × AFL,Bsm
AF = 0.37 × AFL,Liv
A A F
F FL,Liv A,Liv
= = =
total window area (ft2) total floor area of living space, excluding basement (ft2) (perimeter of conditioned floor area of living space with exposed thermal boundary walls higher than 4 feet)/(total perimeter of conditioned floor areas of living space) floor area of basement (ft2) (exposed basement exterior wall area)/(total basement exterior wall area) (total thermal boundary wall area)/(total thermal boundary wall area + common wall area),
total thermal boundary wall is any wall that separates directly or indirectly conditioned space from unconditioned space or ambient conditions, not including unvented crawl space walls; exposed thermal boundary wall is any thermal boundary wall not in contact with soil and not adjacent to a garage or other unconditioned space, and basement exterior wall is any basement wall adjacent to the ground or outside conditions
2 Equation 3 stems from an interpretation of NREL’s Commercial Benchmark (2009) for mid-rise apartment buildings.