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Beyond Net Zero: our involvement with Westminster's Retrofit First policy
Westminster City Council's "Retrofit First" policy marks a significant shift in the built environment's approach to development, and sets a new benchmark for local authorities and planning departments across the country.
We were appointed as independent third-party verifiers for the embodied carbon evidence base underpinning Westminster's policy, which has since undergone review and been formally adopted by the council.
Embodied carbon evidence base
Our role went well beyond a technical sense check. By rigorously interrogating assumptions, baselines and optioneering logic from both conceptual and technical perspectives, we helped ensure that the embodied carbon targets underpinning Westminster’s Retrofit First policy are robust, defensible and practically achievable. We also worked closely with council stakeholders and the original authors to bridge the gap between what is defined in policy and what is realistic in the industry and in actual design practice.
We reframed the conversation towards the fundamental drivers of embodied carbon: geometry, structural logic, façade proportion and overall material intensity. This enabled the evidence base to focus on measures that deliver genuine, system-level carbon reductions rather than through specification of materials from scarce resources or optimistic procurement assumptions (e.g. low-carbon cement using ground granulated blast furnace slag (GGBS), higher recycled content aluminium).
The guiding principles we developed emphasise early design decisions and using less materials. This approach is more resilient to market uncertainty and more likely to result in real construction carbon reductions.
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“At the centre of the review is Westminster’s new Retrofit First policy, placing the city at the forefront of local government action on climate change. The policy requires developers to fully explore all reasonable options for retrofitting and adapting existing buildings before seeking permission for demolition and redevelopment. It recognises that not all buildings can be retrofitted, and therefore takes a retrofit-first, not retrofit-only approach. ”
Embedding insights across our projects
The consideration of embodied carbon has been a core part of our practice for a long time, supported by a dedicated embodied carbon modelling team that works across the full range of our projects. Reviewing the third-party evidence in setting upfront carbon limits for the Retrofit First policy provided an opportunity to test, refine and strengthen the ideas that already sit at the heart of our work. It sharpened how these principles are communicated internally and externally, giving teams a clearer shared framework for assessing what constitutes meaningful, real-world carbon reduction.
We are now applying the same analysis consistently across our projects, testing whether proposed reductions are scalable, whether they rely on genuinely available resources, and whether they risk masking inefficient designs. This has strengthened our internal quality assurance around carbon modelling and optioneering, and improved the clarity and credibility of the advice we provide to clients and planning authorities, helping clients and collaborators move away from short-term optimisation and towards lean, adaptable buildings that are fundamentally lower carbon by design.
Supporting the Westminster Council through our peer review reinforced the importance of translating policy ambition into clear, practical design principles that can be adopted industry-wide.
Beyond Net Zero
This article is part of our Beyond Net Zero whitepaper 2026. The whitepaper is a series of short insight articles and project case studies and is an encapsulation of what we believe as a practice, a summary of what we see as the state of the net-zero nation, and a statement of our intent.
