As cities think about what it means to become “renewable,” many would extend that definition beyond energy used in operations but also embedded in the materials in the form of carbon. In a review of strategies publicly available online, Light House Sustainable Building Centre found that in cases where embodied carbon is addressed, its calculation is not typically comprehensive.
For example, the City of Vancouver’s Green Buildings Policy requires embodied carbon data at the point of permitting, but does not provide a baseline for comparison. LEED 4, on the other hand, requires not only reporting but also comparison with a baseline. The session leaders acknowledged that the different methodologies for assessing embodied carbon, e.g. Life Cycle Analysis, tend to produce different results, as they measure different things and are based on different assumptions. More research is needed to standardize these metrics and indicators.
Molly Steinlage-Cornet delivered a presentation from Brussels Environment in Belgium about a European collaboration that is developing tools for a “circular construction” industry. Currently six pilot projects in four countries are testing the primary pillars of circular construction, which includes “reversible building design.”
Participants held small group discussions about the following questions and then reconvened to share their observations and ideas:
Group 1: What work do cities need to undertake to create baselines and targets?
Group 2: How do Renewable City strategies need to change if we are considering materials?
Group 3: What other policy levers can you think of that cities may want to explore more to push renewable building materials?
Concern that reporting embodied carbon being an onerous task was raised, but participants learned that databases about carbon embodied in materials are already available. That said, in its current form, applied research needs to be made more usable by the private sector.
Participants also wanted to understand the scale of the problem of embodied carbon in comparison with carbon emissions while buildings are in operation, which remains an under-studied question. While the answer is not readily available, it is clear that buildings built to Passive House standards embody more carbon than traditional structures.
Treatment of embodied carbon during retrofit of existing buildings can be addressed through advanced deconstruction techniques that can recover 50-80% of the building materials. Advanced deconstruction also helps identify materials that cannot be reused, thereby informing future design.
Towards accounting for and reducing embodied carbon, participants discussed a variety of strategies. One suggestion was to apply a carbon tax in proportion to the relative carbon intensity of the material. To simplify the process of accounting for embodied carbon, databases of carbon content in materials could be made more accessible by developing apps for the tools and calculators. Participants noted that these should include cost calculators along with the carbon rating/point system and that where precise data are not available proxy indicators should be made available. Related to cost, concern was raised about high land values (relative to the building values) impacting decisions about recovering materials through deconstruction.
From the perspective of building human capacity, there is a need for education and training as well as developing consistent approaches to conducting Life Cycles Analyses. There was also a suggestion to consider development of a certification system that could also evaluate the ethics of how materials are extracted (e.g. clear-cutting) and the impact of their extraction, on the local people and environment, for example. The City of Nanaimo offers homeowners an incentive for using “site-cut timber” in the construction or renovation of their houses.
Programs and policies that were identified as supporting use of more renewable building materials include: easing regulations that restrict wood-frame buildings being limited to 6 storeys (e.g. Building Code); introducing embodied carbon into building codes and re-zoning tools; establishing community and corporate targets; mandating advanced deconstruction techniques; and working with financial institutions to develop ways to incorporate full costs. While there is a need for federal and provincial/territorial/state-level governments to take action, one participant concluded: “City strategies can tell stories and that is important and valuable in itself.”
Session Category : Knowledge Mobilization Workshop