common wall area is the total area of walls adjacent to another conditioned living unit, including basement and directly or indirectly conditioned crawl space walls.
Thirty-three percent of the window area on each facade can be opened for the purpose of natural ventilation.
Either of two approaches may be used to achieve solar neutrality for the Benchmark.
Option 1: The window area calculated above is distributed with the same proportion on each wall and on each floor as the Prototype house. The energy use is calculated with the Benchmark house in each of four orientations rotated in 90° increments relative to the Prototype orientation (+0°, +90°, +180°, +270°), and the average of these four cases is used to represent the energy use of the Benchmark.
Option 2: The window area is distributed equally on each of the four walls (including attached walls), and the orientation of the Benchmark is the same as the Prototype.
Thermal conductance of all thermal boundary elements equal to the requirements, expressed as U values, of Paragraph 502.2 of the 2003 IECC (ICC 2003), as summarized below. Unless otherwise specified, these U-values are for entire assemblies, including sheathing, framing, finishes, and so on.
U-value (Uw) for the opaque fraction of exterior walls from Table 1 or Table 2, as appropriate.
The U-value and solar heat gain coefficient (SHGC) for vertical fenestration, including windows and sliding glass doors, shall be determined using Table 3. The values in Table 3 were calculated based on the HERS methodology for determining maximum window U-value, assuming a floor area to wall area ratio of 1.0. If the simulation tool uses a window library, a window that approximately matches the UF and SHGC shall be selected, and the frame R-value shall be increased or decreased until the overall window UF matches the value in Table 3.
Table 1. Opaque Wall U-Values (Uw) for Detached Homes (excerpted from ICC 2003)
Annual Heating Degree Days Base 65 (HDD65) From Nearest Location
Uw Air to Air, Includes Framing (Btu/h·ft2·°F)
> 13,000 9,000–12,999 6,500–8,999 4,500–6,499 3,500–4,499 2,600–3,499 < 2,600
0.038 0.046 0.052 0.058 0.064 0.076 0.085