CityMakers Voices No.3 — Brogan MacDonald

Her route into the field ran through fashion and art before it found structure, and that designer’s eye still seems to shape how she works — treating existing buildings as material banks, designing from a “fixed kit of parts”, making a virtue of constraint. She calls it inventory-constrained design: the discipline of building beautifully with what a site already holds. It is an argument about carbon reduction in construction, but also about imagination — about how far more interesting buildings can emerge through wise examples of ruse.

Brogan MacDonald joins CityMakers as its latest voice. In the conversation that follows, she makes the case for the buildings we already have — reading the aging city as an inventory of value, a network of urban mines whose concrete frames and steel skeletons hold the very materials from which a lower-carbon future will be built. She is clear-eyed about the economics of reuse, about where policy and the insurance market can move next, and about how an existing building becomes the richer, more creative brief. 

A Chartered Civil Engineer and Chartered Environmentalist, MacDonald led the development of the embodied-carbon calculator now used across more than 100 Ramboll projects. This month, she was named the Royal Academy of Engineering's overall Young Engineer of the Year, winning the Sir George Macfarlane Medal. With the industry's eye on London for Climate Action Week, this is exactly the moment to feature our conversation with the talent citymaker. 

You live and work in a city that never stops building. If someone asks you what sustainable construction looks like in London, where do you begin?

I begin with what is already here. London is dense and deeply layered, so the most sustainable thing we can do is keep using the buildings and assets we already have — first in their current form, and then, where a building has truly reached the end of its life, by reusing the materials inside it. The opportunity becomes obvious the moment you look at the numbers: roughly 60% of all waste in the UK comes from construction and demolition. We have built a fast-moving, extractive economy, and its next leap is to recognize the full value of the materials already in circulation. That shift — seeing the standing city as a resource — is where sustainable construction in London genuinely starts.

Policy tends to trail the conversation. What is your role in closing that gap?

I work at the intersection of a lot of these worlds, so I see my role as bridging them. Architects speak one language, developers another; insurers, funders, and investors each have their own. My job is translation across that whole value chain. Insurers matter enormously here, on two fronts: they carry the rising risks of a changing climate, from flooding to overheating, and they hold a key to innovation, because the bio-based and lower-carbon materials we want to use need to be insurable. The UK tends toward caution with novel materials, which is understandable given its history, so our task as built-environment professionals is to give insurers the technical assurance that these materials perform.

On the policy side there is real momentum: Part Z, a proposed amendment to the Building Regulations, would limit embodied carbon, following the lead of countries such as Denmark and France, where the effect has been to make reuse the default and to set a high bar for new build. Alongside that, a strong, bottom-up movement is doing the work in parallel — groups like the Architects Climate Action Network, Architects Declare, and Structural Engineers Declare, on whose steering group I sit.

Looking at the next five years, where do you see the most hope?

In refurbishment. Working with an existing asset can bring real cost advantages, depending on the building’s constraints, and it is simply more rewarding work — technically richer, more demanding, and frankly more fun than starting from a blank site. It also reads beautifully against a company’s sustainability goals: fewer resources consumed, stronger local supply chains, real social value. Over the past 18 months, I have watched the refurbishment-and-reuse space grow markedly, to the point where many designers now actively target it, setting themselves goals of, say, 30% of their portfolio in reuse. That is a genuine shift in the direction of the profession’s ambition.

Does that stock actually exist in London? Can we make more with what we already have?

Absolutely — we are sitting on urban mines. These buildings are full of excellent materials, and the work now is making the numbers stack up so that recovering them becomes the obvious choice. It helps to remember that this is how we have always built. Before industrialization, reuse was simply the norm; you worked with what you already had. In many countries across the Global South, buildings are still carefully taken down precisely because the materials hold such value. There is real wisdom in returning there. The materials are here, in quantity — the task is to build the incentives and the design culture that let us use them well.

Public consciousness has caught up with aviation and fast fashion. Why has the built environment stayed below the radar?

That is the fascinating gap. People understand the environmental costs of a flight and of fast fashion; the built environment deserves the same shared awareness. Cement alone accounts for around 8% of global emissions, so the foundations of a house carry a far bigger story than most people realize. Making that story accessible is something I care about deeply, because once it lands, the logic of reuse becomes irresistible. The encouraging truth is that almost any sound building can find a second life. A structure that has outgrown its use as a commercial office can make a wonderful hotel, student housing, or shopping center. The building stays; the use evolves. That is a hopeful message, and it deserves a wider audience.

Give us an example where reuse simply worked — where the result was better for everyone.

Two come to mind. In Sydney, Quay Quarter Tower by 3XN took an existing skyscraper and carved and recomposed it into something spectacular — a wholesale reuse of structure that served the client brilliantly and kept a great deal of material in play. Closer to home, I spent years on a 1950s concrete-framed hotel in Mayfair. The client was open to demolishing and starting again, and we offered them something better: keep the building and grow it. We extended upward, outward, and even downward. London’s planning rules protect key views of St Paul’s, so where we reached the height limit we went below, jacking up the whole building and extending the basement. By retaining that frame we saved 5,000 tonnes of demolition waste and 3,500 tonnes of carbon. Much of this work happens quietly, behind hoarding for years; a building can look much the same from the street while something remarkable takes shape within.

Final question. For everyone working in city-making, where does the real opportunity lie?

The opportunity is in the materials and building types we already have. The shift is to see existing buildings as material banks — as urban mines — and to design from an inventory: a fixed kit of parts, almost like being handed a catalog and asked to build something wonderful from exactly what is in it. I call it inventory-constrained design, and I find it genuinely liberating. We work from a finite, precious stock of materials, and there is deep value in honoring that, because every tonne we extract anew carries a cost beyond carbon — quarrying and mining drive significant biodiversity loss, which we are only beginning to measure properly. So the great opportunity and the great creative challenge are to make beautiful, lasting places from the abundance already standing around us. That is the work I am most excited about.

This interview is part of CityMakers Voices, a conversation series from the Holcim Foundation that gathers the thinkers, designers, and decision-makers whose work shapes the cities we live in. They form part of CityMakers, a new resource focused on the people, places, and programs revitalizing the urban realm.