Influence of Architectural Details on the Overall Thermal Performance of Residential Wall Systems

Abstract

Predicted heat losses through building walls are typically based on measurements of the wall system clear wall area using test methods such as ASTM C 236 or are calculated by one of the procedures recommended in the ASHRAE Handbook of Fundamentals that often are carried out for the clear wall area exclu sively. In this paper, the phrase "clear wall area" is defined as the part of the wall system that is free of thermal anomalies due to building envelope subsystems, or thermally unaffected by intersections with other surfaces of the building envelope. These experiments or calculations normally do not include the effects of building en velope subsystems such as corners, window and door openings, and structural joints with roofs, floors, ceilings, and other walls. These details represent completely different constructions; it is apparent that the thermal properties measured or calculated for the clear wall area may not adequately represent the total wall system thermal performance. Factors that would impact the ability of today's standard prac tice to accurately predict the total wall system thermal performance are the accuracy of the calculation methods, the amount of the total wall area that is clear wall, and the quantity and thermal performance of the various wall system details. Based on 3-D finite difference computer modelling, the thermal performance of several typical wall systems including various system details have been analyzed, and the overall wall system thermal performance for a typical single-story ranch house has been determined. These data are compared to typical experimental and analytical techniques to ascertain their precision in predicting the overall wall system perfor mance.