A guidance document we take seriously
The Institution of Structural Engineers' guidance on circular economy and reuse, and its companion document on calculating embodied carbon, shape how we approach every existing-building project. Its core argument is straightforward, even if the industry has been slow to fully act on it: embodied carbon — the emissions locked into a building through the extraction, manufacture and transport of its materials — is not a secondary consideration to operational energy performance. For an increasing number of projects, it is the larger of the two, and it is entirely front-loaded, spent the moment concrete is poured or steel is fabricated.
Why retention usually wins the arithmetic
IStructE's guidance describes reuse and retention as ‘critical’ to the industry's path to net zero. A retained structure has already spent its embodied carbon; extending its life is very rarely as costly as demolishing and rebuilding, because demolition itself carries a carbon cost. We see this arithmetic play out directly on the projects that make up the majority of our work: a Victorian cast-iron guide frame retained as a landmark feature within a residential redevelopment, rather than demolished, keeps a century and a half of embodied carbon in productive use.
IStructE's position: reuse and retention are critical to the structural engineering profession's path to net zero — and structural engineers need to be able to quantify the carbon savings of reuse rigorously, not simply assert them.
The engineering discipline behind ‘why not just reuse it’
Retention is not automatically the right or easy answer. Existing structures were designed to codes and load assumptions that may be decades or centuries old, and confirming that a historic frame or floor can safely carry new, often heavier, loads is genuinely demanding technical work — applying recognised guidance for the appraisal of existing iron, steel and timber structures, careful allowance for a century or more of prior loading history, and conservative engineering judgement where records are incomplete. Done properly, this kind of assessment routinely confirms that historic structures have more remaining capacity than a cautious first assumption might suggest.
“A structural appraisal that arrives early can identify genuine reuse potential a design team didn't know existed. One that arrives late is often just confirming decisions that have effectively already been made.”
Retrofit-first as a default, not an exception
One of the more useful shifts IStructE's guidance encourages is treating retention and adaptive reuse as the default starting position for any existing-building project, with demolition needing to be actively justified rather than assumed. In practice, that means our involvement increasingly starts before a scheme's structural strategy has been fixed — at the point where a client or design team is still weighing whether to retain, adapt or replace, rather than being brought in afterwards to make a demolition decision structurally workable.
Beyond structure: materials and genuine circularity
The circular economy principle extends further than keeping a building's frame standing. It also asks whether individual components — structural steel, reclaimed timber, masonry units — can be catalogued and reused elsewhere when a building genuinely does need to come down. We've applied this thinking directly on a major redevelopment site, creating detailed inventories and reuse pathways for an onsite material bank ahead of construction — practical, unglamorous work that directly reduces embodied carbon by keeping usable material in circulation.
The client conversation this actually requires
The biggest barrier to retention-first structural strategy is rarely technical — it's that the carbon case for reuse has to be made explicitly, in terms a client or funder will actually weigh alongside cost, programme and risk. That is the conversation we try to have on every existing-building project from the earliest possible stage: not whether sustainability matters, but what retention specifically, credibly, makes possible on this building, for this use — and what it would cost, in carbon and in cash, to choose otherwise.