**2.1 Environmental sustainability**

As Canadian cities face the increasing global impacts of climate change, ongoing environmental degradation and higher energy costs, planners and policymakers have placed significant emphasis on addressing environmental sustainability in the built environment. The physical form and location of built heritage represent a key opportunity for cities to make progress towards environmental targets by focusing on reuse, recycling and redevelopment of existing housing. This supports circular economy strategies that minimise environmental impact by extending the use of materials and reducing the consumption and waste of materials and energy. Retrofitting and adaptively reusing existing heritage buildings for housing purposes represents a significant opportunity to promote more sustainable uses of renewable and non-renewable resources. Circular economy strategies call for a cultural shift within the construction and development industries, to view buildings as reusable resources as opposed to consumable products to achieve desired sustainability outcomes [12, 13].

Notwithstanding the progress made on the technical side to increase the sustainability and energy efficiency of existing housing through energy efficiency retrofits, tensions often arise between building preservation and conforming to current regulatory requirements. While many current building and energy codes emphasise more environmentally sustainable building practices, retroactively updating older buildings to these standards can act as a barrier to building reuse and threatens the financial viability of a project. In light of these tensions, and additional factors around density, location and building condition, studies have found that incentives and flexibility in planning and housing policy administration are needed to ensure retrofits and adaptive reuse projects in existing heritage buildings are successful and desirable [13, 14].
