Thermal Bridging and Linear Thermal Transmittance Calculations for Balconies

Abstract

The thermal performance of building envelopes can be significantly affected by thermal bridging. Thermal bridges are localized areas of high heat flow through walls, roofs, and other insulated building envelope components. Thermal bridging is caused by highly conductive elements that penetrate the thermal insulation or misaligned planes of thermal insulation (or both) within the building envelope. These paths allow heat flow to bypass the insulating layer and thereby reduce the effectiveness of the insulation. The architectural look of exposed slab edges and protruding balconies or eyebrow elements in contemporary buildings is becoming increasingly common; however, the impact of floor slab edges and balconies on the thermal performance of the building is not well regulated. In this study, the impact of adding a balcony to a wood frame wall assembly was studied experimentally. Two wood frame wall assemblies were tested in the National Research Council’s guarded hot box test facility in Ottawa, ON, in accordance with ASTM C1363-19, Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus. The first test included a wall assembly without a balcony. The second test consisted of a wall assembly with a balcony. The linear transmittance value was calculated for the balcony. COMSOL Multiphysics software was also employed to model the wall assemblies, and the results from the three-dimensional simulations are included.