Life cycle GHG assessment of a building restoration: Case study of a heritage industrial building in Toronto, Canada

The refurbished Don Valley Brick Works’ Kiln Building, in Toronto, Canada, now the TD Future Cities Centre, is designed to have net zero carbon emissions. This is to be achieved through the reuse of existing materials and structures, selection of lower-carbon materials purchased from local sources, installation of renewable energy systems, natural lighting and improved thermal insulation of the building’s envelope, as well as developing a carbon offset strategy. The heritage designation of the building imposed restrictions on the design of the project (e.g., preventing insulation of exterior walls). In collaboration with the owner and constructor, the project team completed a life cycle assessment (LCA) consisting of an assessment of embodied emissions of the building’s restoration from cradle to grave, accompanied by a scoping estimate of greenhouse gas emissions associated with its future operational energy use. Primary construction data for the newly-added materials, transport, and construction activities were used. Life cycle inventory analysis and impact assessment were implemented in the One Click LCA software. Use phase carbon intensity was estimated using design and literature data. In addition to the ‘core and shell’ LCA scope typically applied to buildings, the team also tracked materials and processes that are often not included in building LCA studies such as HVAC, plumbing, and renewable energy systems.Embodied carbon for the restoration project, assuming a 60-year lifetime, is calculated as 1250 tonnes carbon dioxide equivalent (tCO₂e). Sixty-nine percent of the carbon comes from the materials (extraction to manufacturing) used in construction, 20% is due to replacement of materials during the building’s service life, and most of the remaining 11% is from on-site construction energy (5%) and waste disposal at end-of-life (4%). The main building elements contributing to the embodied carbon are the renewable energy systems (31%) and the raised concrete floor (26%). Building envelope and foundation play minor roles, as they are mostly pre-existing. The embodied carbon added to the building through the restoration project is forecast to be balanced by savings in operational energy related to heating, cooling and lighting, within 3–13 years, depending on whether natural gas or electricity use are avoided, respectively.Uncertainties in the analysis arise from partial or missing data, modeling assumptions and future scenario unknowns. The model is sensitive to the useable lifetime of the building, local or non-local sourcing of building materials, modeling of certain components used in large quantities, and changes in the recycled content of steel. This study of a net zero carbon refurbishment project of a heritage building provides insights for assessments of future projects as such refurbishments become more commonplace. The methods and recommendations regarding data sources, data collection, and approach to uncertainty evaluation will be useful for LCA of any construction project.