Last year, the Canada Mortgage and Housing Corporation (CMHC) commissioned MMM Group Limited (MMM) to determine the most important factor in achieving a high-performing multi-unit residential building (MURB) in Canada. Given the increasing importance of MURBs in Canada, this study will have far reaching implications for many in the development and building design industry.
With a third of Canadians living in apartment buildings and condos, MURBS are one of the fastest-growing sectors of the urban building industry in Canada. Particularly in land-scarce cities, such as Toronto, the skyline will continue to fill with those ubiquitous high-rises – which already account for a quarter of our building energy use. So the question of how to build the most energy-efficient MURB possible is extremely important to cities, architects, and organizations like the CMHC.
It is commonly understood in the Canadian building industry that the architectural form of a building, from the building massing to façade treatment, has a significant impact on its heating and cooling loads. However, few studies have examined the impact of architectural form on energy performance, and in particular for MURBs in Canada.
In 2013, CMHC commissioned MMM Group, led by energy modeling expert Steve Kemp (Manager, Buildings – Sustainability), to determine the most important factor in achieving a high-performing MURB in Canada. As part of the study, the engineering team created a custom eQuest script and modeled an unprecedented 6,000 possible combinations of building designs to determine the connection between form and efficiency, including looking floor plate, orientation, envelope, and height.
The study determined the most important design parameter in heating and cooling loads was the performance of the envelope façade elements themselves.
Namely the insulating performance of the walls, the insulating performance and solar gain performance of the windows, and the relative ratio between these two façade elements represented by the window-to-wall ratio.
Heating and Cooling Energy Cost
*Plotted values are selected from the complete 6,000 point data set, but are representative of the trend. They represent an “L” shape floorplate at various orientations and selected envelope assemblies. The trend shown is that as the envelope performance improves (lower window to wall ratio, higher R-values, etc.) the energy costs decrease and the effect of orientation diminishes.
So if a building designer is looking to create a high-performance MURB, look away from the popular glass box design and towards a window-to-wall ratio of 30-40% with window and wall performance that meet or exceed the prescriptive requirements of ASHRAE 90.1-2013 (typically an effective R-18 or greater with low-e + argon windows). This strategy was used at the 77 Governor’s Road condo building in Dundas, Ontario. MMM Group’s team helped design this building in 1997, and it is still one of the most energy-efficient MURBs in the country (using 137 kWh/m2 compared with the Canadian MURB average of 358 kWh/m2). At this MURB, high-performance windows have insulated concrete frames. Additionally, the walls have R22 insulation to eliminate thermal bridging and moisture transfer. The concrete balconies are all thermally broken.
The conclusion to be communicated to the architectural design community should be that high-performance envelopes allow architecture freedom with the massing and orientation of the building without a significant impact on the resulting energy performance.