The Level(s) Interview: Sara Dethier

In this edition of The Level(s) Interview, we speak to Sara Dethier, Senior Consultant, Climate Change and Sustainability at Arup. Sara is working on a project that’s focused on affordable and low environmental impact housing by efficiently using the existing building stock.

What made your organisation keen on working on this topic and drive this agenda forward? 

The European built environment faces a twin challenge: a growing affordability crisis and the need to decarbonise its economy. We are keen to advance this agenda because measures aimed at making a better use of existing buildings and land connect these goals in a practical way.

Measures to efficiently use existing buildings include space sharing and rightsizing, renovation and refurbishment, conversion and adaptive reuse, as well as densification and regeneration. Done well, this can reduce demolition and new-build demand, cut whole-life carbon and waste, limit sprawl and land take, and unlock homes faster and more affordably.

Our consortium, made up of Arup, BPIE, ifeu, Öko-Institut, négaWatt, and Dark Matter Labs, brings a strong mix of policy, delivery and systems expertise across EU, national and city levels, and we see this work as a chance to help turn ambition into implementable pathways.

What do you believe the project will be able to contribute to? 

The project will provide an evidence base and actionable recommendations to scale measures which make a more efficient use of the existing building stock across Europe, so that affordability and low environmental impact can move together rather than competing.

In the project, we will map and assess measures that support better use of existing buildings, and their success factors, and analyse the building and spatial policy levers that can unlock them. We will also compare them to demolition and new construction case studies and propose a practical framework for collecting and monitoring data on vacant and underused space.

What do you think will be the biggest challenge? 

A key part of the work is identifying the most promising ways to make better use of existing buildings, but also land, and assessing how they can be scaled across different contexts in Europe to unlock additional affordable supply.

The biggest challenge will be upscaling – moving from strong local examples to credible, EU-relevant estimates and policy guidance. This depends on where demand is strongest, which building types and neighbourhoods can accommodate change, and whether the right policy mix is in place.

These can include planning and zoning for conversions and gentle densification, to retrofit-first/demolition rules, brownfield/infill-first policies, and measures that bring idle space back into use, such as vacancy/underuse charges. Evidence and data vary across countries, so we will need to be transparent on sources and assumptions.

How do you see it fitting into the overall policy agenda (e.g. the EU Affordable Housing Plan and the upcoming Circular Economy act)?

We see the project as a connector across policy strands often treated separately: affordability, decarbonisation, circularity and land use. It will support the implementation of the European Affordable Housing Plan by showing how better use of existing buildings and plots can deliver homes while avoiding the upfront carbon and resource impacts of new construction, which are an even bigger issue if using greenfield sites.

It aligns with the circularity agenda by prioritising renovation, refurbishment and adaptive reuse, and links to tools such as digital building logbooks. It also supports the EU’s No Net Land Take objective by reducing sprawl. In short, measures aimed at making a wiser use of our buildings stock mutually reinforce these agendas.

How will you involve stakeholders during the course of the project?

Stakeholder involvement is embedded from the start as a key part of the study and accounts for a substantial share of the work. It will help guide the analysis and ensure that the findings and recommendations reflect practical experience.

We will develop a stakeholder map and engagement plan with the European Commission, then involve relevant groups at key moments through interviews, surveys, data collection and targeted workshops. A key milestone will be an in-person expert workshop in Brussels to test emerging findings and co-develop recommendations, with balanced representation across geographies and expertise.

Stakeholder input will be integrated across deliverables, ensuring outputs are practical, relevant and usable. This ongoing engagement will be used to test interim findings and refine the final recommendations.