BuildwiseRetrofit first: why renovating often beats rebuilding
Reusing an existing structure saves embodied carbon and often time. We look at when a retrofit is the smarter route.
By Buildwise Editorial2 min read
The greenest building is often the one that already exists. Reusing a structure avoids the carbon locked into new concrete, steel and foundations, and increasingly that carbon is what decides whether a scheme is approved at all.
The carbon case
Most of a building’s embodied carbon sits in the frame and foundations, laid down long before anyone moves in. Demolishing a sound structure to build a new one throws that carbon away and adds the emissions of a new build on top, a double cost that a retrofit simply avoids. For many building types, keeping the frame and replacing everything else cuts embodied carbon by half or more compared with starting again, even before the operational savings of a better envelope are counted.
When retrofit makes sense
A sound frame, generous floor-to-floor heights and a good location are strong signs that reuse is worth pursuing. Building services and envelopes can usually be replaced while the structure stays, which means a retrofit does not have to mean keeping everything: it means keeping the parts that are expensive and carbon-intensive to replace, and renewing the parts that age fastest anyway, such as windows, cladding and plant.
Floor-to-floor height deserves particular attention early on. A structure with limited headroom leaves little room for the new services, insulation and raised floors a modern building needs, and can rule out retrofit on its own regardless of how sound the frame is.
Watch-outs
Survey early, before the scheme is fixed rather than after. Hidden defects, hazardous materials such as asbestos, and limited access for new services can eat into savings quickly, and finding them after design is complete is far more expensive than finding them before.
Structural capacity is the other recurring surprise. An older frame was designed to older loading standards, and a change of use, such as converting offices to housing, can trigger strengthening work that offsets some of the carbon saved by keeping the structure in the first place. A structural survey against the intended new use, done early, avoids discovering this mid-design.
Making the numbers work
Retrofit projects often carry more risk in the early stages, because so much depends on what a survey finds once work starts opening up the building. Budgeting a realistic contingency, and sequencing the most uncertain work early so it can inform the rest of the design, keeps that risk from derailing the programme later.
Value for owners
Lower energy bills from a better envelope, stronger appeal to tenants who increasingly ask about a building’s carbon footprint, and often a faster route to occupancy than starting from a cleared site. Planning consent can also move faster for a retrofit in areas where policy actively discourages demolition, which is now the case in a growing number of jurisdictions.
