A science-based path to circular construction in Spain

1. The roadmap aims to move the sector from a waste-generating to a value-generating model. From Ramboll’s perspective, what are the most critical shifts the construction industry must make in the next 5–10 years to turn that ambition into reality?

Jonathan: The industry must move from a linear build-use-demolish model to one centred on sufficiency and efficiency. That means building less where possible, reusing and intensifying the use of existing stock, and designing for longer life and adaptability. We also need to create a functioning market for secondary and reused materials. At the moment, it is often cheaper to use virgin materials than to selectively deconstruct, verify, and reuse components. Finally, densification and retrofitting are key levers. By adding stories, repurposing mono-functional buildings, and prioritising renovation over demolition, we can reduce demand for new resources and lower absolute emissions. Though such project may feel like a very technical number-driven exercise, it is also an invitation to think about how this industry fundamentally operates in Spain, and naturally beyond.

Ricardo: Three shifts are critical. First, we must reverse the default from new build to refurbishment. This is the single largest lever to reduce material demand in the short term. Second, we need to operationalise circularity through tools such as digital material passports and design-for-disassembly standards, so that reuse becomes scalable rather than bespoke. Third, we must align incentives. Today, economics still favour virgin materials and demolition.

What makes this challenging is not the technical feasibility, but system coordination. Circularity decisions are often made too late in the process. Embedding them at the concept stage, across designers, contractors, clients, and authorities, is where real change happens.

2. Ramboll highlights a “science-based” approach aligned with planetary boundaries. How does that translate into practical decision-making for developers, designers, and policymakers?

Ricardo: We apply planetary boundaries to decision-making by setting absolute limits, such as a carbon or material budget, for each project, city, or sector. This approach shifts the focus from relative improvement to operating within a defined ceiling. In practice, this approach changes design decisions. For example, a developer may need to prioritise reusing an existing structure or selecting lower-impact materials, not because they are slightly better, but because they are the only options that keep the project within its resource budget. By grounding these thresholds in science and validating them with academic input, we turn abstract sustainability goals into clear decision-making rules.

Jonathan: Starting with science somewhat reduces the debate about values and gives the industry a common benchmark. Many organisations already set science-based targets for decarbonisation. By extending that discipline to materials and absolute impacts, developers and designers can make decisions that are consistent with planetary limits. In short, science-based targets become operational decision rules, by choosing solutions that help stay within the defined budget for resources and emissions.

3. The initiative acknowledges challenges beyond waste, finance, regulation, and supply chains. What role can engineering and advisory firms like Ramboll play in unlocking progress?

Ricardo: The core barrier is that circularity is still economically invisible in most decisions. Asset valuations, procurement models, and cost plans rarely capture long-term value, which means circular solutions struggle to compete with lower upfront-cost alternatives. This creates a structural bias toward linear outcomes, even when better options exist.

Ramboll addresses this gap by quantifying long-term value, reducing risks in circular strategies, and developing viable business cases. In addition to advisory services, we support clients in testing solutions through pilot projects, enabling circularity to progress from concept to proven practice.

Jonathan: Regulation has arguably proven to be the strongest lever in Europe. Incentives help but they are rarely sufficient on their own. Engineering and advisory firms can support policy by supplying the technical evidence, modelling, and roadmaps that can put regulation into practice, and this is what we’re striving to achieve through this project. We can also accelerate supply‑chain change through digitalisation and innovation in materials and design practices, etc. Digital passports and material banks improve traceability and create the conditions for a secondary materials market. Collaborative projects across disciplines and with governments will be essential as it provides replicability and predictability to market players.

4. Looking ahead to 2050, what would success look like for this roadmap? Are there specific indicators or milestones Ramboll believes are essential to track progress toward a truly circular built environment?

Ricardo: Success in 2050 means the built environment operates within planetary limits while continuing to deliver social and economic value. In practical terms, buildings become material banks, and reuse is the default rather than the exception. Beyond minimising harm, projects should actively enhance ecological and social capacity. This means moving toward net-positive design principles, where buildings sequester more carbon than they emit, create ecological space equivalent to or greater than their footprint, and rely on nature-positive supply chains.

From a social perspective, success also implies that projects promote fairness and resilience by providing universal access to essential environmental services, such as healthy indoor environments and climate protection, while addressing historical deficits. Economically, it requires strengthening the biophysical foundations of the economy, shifting value creation away from resource-intensive and luxury consumption toward long-term system health. What matters is not just tracking indicators but embedding them into decisions. Targets for renovation rates versus new build, minimum shares of reused materials, and net-positive performance thresholds should directly shape planning approvals, investment criteria, and design processes. If these indicators are actively steering decisions rather than passively reporting progress, we will know the transition is working.

Jonathan: From a climate perspective, success means staying within the sector’s carbon and material budgets. That requires measurable milestones, with legally defined carbon budgets per sector, a declining absolute footprint even while society grows, clear targets for reuse and renovation rates, and improved environmental metrics. I believe we also need to supplement the narrative with other metrics that demonstrate that overall the industry delivers higher benefits to society while staying within the defined boundaries. Naturally, we could think of CO2 intensity levels, but we should also , for example, consider the happiness of building users or the reduced sickness-related absences in commercial buildings. If we can reframe the rules of the game so that we do more with less, and measure progress with science‑based KPIs, the roadmap will have delivered on both its climate and societal promises.