Multi-unit residential buildings (MURBs) are vital component of the Quebec social housing stock which have largely fallen into disrepair. Panelized deep energy retrofits represent an exciting opportunity to revitalize them by improving their construction quality and energy efficiency alongside the health and wellbeing outcomes of their residents. Crucially, the success of these retrofits depends on mitigating each candidate building's thermal bridges. These occur wherever the building's envelope is non-continuous (such as at the junctions of architectural components) such that direct heat transfer between its interior and exterior is possible. This phenomenon, called thermal bridging, often occurs at balcony protrusions. In fact, exposed balcony supporting slabs represent the second greatest source of building heat loss after openings and glazing.

Fortunately, many solutions exist to manage these thermal bridges. Among them are enclosing balconies or over-cladding them, sealing junction gaps with aerogel insulation, installing structural thermal breaks or replacing existing balconies with free-standing alternatives. This work investigates these retrofit solutions as applied to a typical MURB.

Thermal analysis was conducted on each detail to compare the interventions’ impacts on the RSI (R-value, measure of a material’s resistance to the flow of heat, in SI units) of the building envelope. These analyses indicated that the outright replacement of existing balconies with a free-standing option was the solution least prone to thermal bridging (while also being highly replicable across the housing stock). Still, further research is required to resolve its design (including the balcony-door junction and overall load handling) and holistically evaluate it and the other potential solutions through energy modelling, cost estimation and life cycle analysis (LCA).