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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 sunrooms

  • 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).

Equation 1:

AF = 0.18 × AFL,Liv

× FA,Liv

  • +

    0.18 x AFL,Bsm

× FA,Bsm

Equation 2:

AF = (0.18 × AFL,Liv

× FA,Liv

  • +

    0.18 × AFL,Bsm

× FA,Bsm

)× F

Equation 3:2

AF = 0.37 × AFL,Liv

× FA,Liv

×F

where:

A A F

F FL,Liv A,Liv

= = =

A F

FL,Bsm A,Bsm

= =

F

=

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),

and where:

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.

3

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