Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Your calculation is missing the thermal bridging due to the parapet. The parapet length is the length of the roof-wall intersection, which is equivalent to the perimeter of the building (302.82 ft). The psi-factor for wood-framed wall parapet is 0.32 (unmitigated and mitigated are the same factor).
Therefore, the total unmitigated heat flow impact (∑ΨiLi + ∑Xinj) is 4400.15 + 302.820.032 = 75.69. Divide this by the total opaque wall area (2341 ft2) yields the Thermal Bridge Adjustment for AGW U-factor of 0.03233 (unmitigated) or 0.0227 (mitigated).
The derated u-factors (assuming 0.051 u-factor requirement in CZ5):
2019 (unmitigated): 0.051 + 0.032 = 0.083
2022 (mitigated): 0.051 + 0.023 = 0.074
| | 2 | No.2 Revision |
Your calculation is missing the thermal bridging due to the parapet. The parapet length is the length of the roof-wall intersection, which is equivalent to the perimeter of the building (302.82 ft). The psi-factor for wood-framed wall parapet is 0.32 (unmitigated and mitigated are the same factor).
Therefore, the total unmitigated heat flow impact (∑ΨiLi + ∑Xinj) is 440440 * 0.15 + 302.82302.82 * 0.032 = 75.69. Divide this by the total opaque wall area (2341 ft2) yields the Thermal Bridge Adjustment for AGW U-factor of 0.03233 (unmitigated) or 0.0227 (mitigated).
The derated u-factors (assuming 0.051 u-factor requirement in CZ5):
2019 (unmitigated): 0.051 + 0.032 = 0.083
2022 (mitigated): 0.051 + 0.023 = 0.074
The thermal bridging assumptions and calculations used in the prototypes will be detailed in a paper presented at the 2026 Winter ASHRAE conference (pending acceptance).
