Collect your retrofits: Parametric modelling to support homeowner energy retrofits in heritage buildings at the early design stage

The joint deployment of energy reduction actions across multiple buildings at once is much needed to reach climate targets, but collective decision-making with shared ownership is a complex process. Each homeowner is accountable for their own energy use, while being constrained by their personal financial capacity and will to act with other co-owners. At the same time, decision-making for energy retrofits involves multiple constraints and criteria, relating to divergent and sometimes conflicting technical, environmental, economic, and social issues, leading to a fragmented response to the retrofitting challenge. This article presents a community-led approach to energy retrofit based on parametric modelling and design space exploration. The approach was tested under the conditions of a homeowner association residing in a heritage building in Amsterdam. Cards displaying each retrofit option and its associated impacts in terms of costs, operational carbon emissions, and energy performance were designed to facilitate negotiation between the participants and their interaction with the computational model. The intention was to empower the group by enabling the exploration of various design alternatives and to nourish conversations about sustainable retrofitting that would normally not take place. Participant feedback shows that the approach effectively improved the quality of the discussion and increased their understanding on the pathways to make their building more sustainable. This article presents the Collect your Retrofits project and describes the potentials and limitations of using parametric modelling to facilitate group decisions made at early stages of retrofit design.