The carbon cost of a new commercial building is incurred before the first tenant moves in. Cement production alone accounts for roughly 8% of global CO₂ emissions. Calcining limestone releases CO₂ chemically, on top of the fossil fuel burned to heat kilns to around 1,450°C. Structural steel is similarly energy-intensive. Blast-furnace routes emit around two tonnes of CO₂ per tonne of steel, so every new transfer beam and column section adds a measurable carbon liability to the asset.
Structural engineers quantify this liability in kilograms of CO₂ equivalent per square metre (kgCO₂e/m²), following the RICS whole-life carbon methodology. The results consistently show that the substructure and frame make up the largest share of upfront embodied carbon. A deep fabric retrofit keeps the concrete core and foundations and upgrades the glazing, HVAC and insulation. In doing so it can avoid up to 70% of the embodied carbon a replacement building would incur.
Metric (office, per m² GIA) | Demolish and Rebuild | Deep Fabric Retrofit |
|---|---|---|
Upfront embodied carbon (modules A1–A5) | Typically 800–1,200 kgCO₂e/m² | Typically 200–400 kgCO₂e/m² |
Substructure and frame | Fully replaced: new piles, slabs, columns and cores | Retained: existing concrete frame and foundations reused |
Demolition and waste (module C of existing asset) | Full strip-out, crushing and haulage | Limited to façade, services and finishes |
Operational performance | EPC A achievable | EPC A–B achievable with new glazing, HVAC and insulation |
Carbon payback against retention | Often 30–50 years | Savings start on completion |
Planning exposure | WLCA scrutiny for large London schemes | Strong alignment with retention-first policy |
For asset managers, this is a financial issue as much as an environmental one. Large London schemes must already submit a WLCA under the London Plan, and planning decisions increasingly test whether demolition has been justified against a retention option. Occupiers with Scope 3 reporting obligations are beginning to ask about embodied carbon as well as operational ratings. A demolition-led strategy that looks efficient on an EPC can therefore carry a hidden carbon surcharge into valuation, letting and planning risk.
The pragmatic conclusion is retention first. Developers who start with a structural survey and retrofit feasibility study are best placed to protect asset value and decarbonise at the pace net zero demands.