Carbon arithmetic
Typical London 4-bed 1900 terrace 145m². Demolish + rebuild new: A1–A5 ~600 kgCO2e/m² × 145m² = 87,000 kgCO2e embodied. C1–C4 demolition of existing ~75 kgCO2e/m² × 145 = 10,875 kgCO2e. Total upfront 97,875 kgCO2e. Operational B6 new build EPC B = ~1,200 kgCO2e/year × 60 years = 72,000 kgCO2e. Whole-life ~170,000 kgCO2e. Deep-retrofit existing terrace: A1–A5 ~210 kgCO2e/m² × 145 = 30,450 kgCO2e (insulation, glazing, ASHP, MVHR, services). C1–C4 retained ~25 kgCO2e/m² × 145 = 3,625 kgCO2e. Operational B6 retrofit EPC B = same 72,000 kgCO2e. Whole-life ~106,000 kgCO2e. Retrofit saves 64,000 kgCO2e (38% reduction) over 60-year life. Carbon payback of rebuild: ~never reached vs equally-efficient retrofit.
When rebuild justified
Limited cases: (1) existing structure unsalvageable (severe subsidence, fire damage, structural collapse risk); (2) site density uplift more than doubles dwellings (apartment block replacing single house increases functional units served per kgCO2e); (3) existing building Cat E EPC + impossible to retrofit (rare — most retrofits viable). Conservation areas + listed buildings — demolition not permitted regardless of carbon math. RIBA + LETI Retrofit First guidance + GLA Circular Economy Statement policy push retention as default.
Planning policy alignment
London Plan 2021 Policy SI 7 (Reducing waste + supporting circular economy): demolition only justified if economically + technically unfeasible to retain. Westminster, Camden, Islington, K&C, LBHF Local Plans all incorporate retain-first policy. Whole-life carbon assessment for any application proposing demolition mandatory in Camden, increasingly across other boroughs. Planning officers will challenge demolition proposals lacking compelling case.
