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What Is Embodied Carbon in a London Renovation?

Embodied carbon = upfront CO2e released by extracting, manufacturing, transporting + installing materials (modules A1–A5 of EN 15978). Typical London extension 350–550 kgCO2e/m². Concrete, structural steel, aluminium, foam insulation dominant. RIBA 2030 Climate Challenge target 625 kgCO2e/m² whole-life. Reduce via timber frame, low-carbon concrete, mineral insulation, reclaimed brick.

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01

Definition + boundaries

EN 15978 lifecycle modules. A1 raw material supply. A2 transport to factory. A3 manufacturing. A4 transport to site. A5 construction + waste. A1–A5 = upfront embodied carbon (what's locked in before occupation). B1–B7 = in-use (maintenance, replacement, refurbishment, operational energy + water). C1–C4 = end-of-life (demolition, transport, processing, disposal). D = beyond-life (reuse, recycling benefits). Embodied carbon (A+B+C-D) increasingly dominant as buildings get more operationally efficient — for new Passivhaus standard, embodied > operational over 60-year life.

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Typical hot-spots in London extension

Concrete substructure (foundations, slab) 25–35% of A1–A5. Structural steel beams + columns 10–18%. Aluminium bifold/sliding doors 8–14%. PIR/PUR foam insulation (Kingspan, Celotex) 8–12%. Brick + block 8–14% (UK brick 0.21 kgCO2e/kg; concrete block 0.10; reclaimed brick ~0.005). Glazing 4–8%. Plasterboard 3–6%. Finishes 5–10%. Worst-case stacked-spec all-aluminium / steel-frame / concrete-rich extension 600–750 kgCO2e/m². Best-case timber-frame / lime-mortar / reclaimed brick / wood-fibre insulation 180–280 kgCO2e/m².

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Reduction strategies (substitution hierarchy)

1. Don't build (use existing). 2. Build less (smaller footprint, multi-functional space). 3. Build clever (timber frame instead of steel where spans allow; reclaim materials; specify EPD-backed low-carbon products). 4. Build efficient (insulate well, design for long life + future adaptability). 5. Build clean (low-carbon concrete with GGBS/PFA 50%+ replacement; FSC timber; mineral-wool not PIR). Quick wins: GGBS-replacement concrete (–30% A1–A3); timber I-joists vs steel beams where span <5m; reclaimed London stock brick (–95% vs new); wood-fibre rigid insulation (Steico, Pavatex) vs PIR (–60%); aluminium-clad timber windows vs full aluminium (–40%).

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How do I measure embodied carbon on my renovation?

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Whole-Life Carbon Assessment per RICS Professional Statement 2nd ed (2023). Quantity surveyor or sustainability consultant calculates A1–A5 from bills of quantities × ICE database / EPD carbon factors. Cost £1,850–£4,850 for typical London extension. Required on RIBA 2030 Climate Challenge submissions + some local plan policy applications (Camden, Islington, Westminster increasingly).

Is renovation lower carbon than rebuild?

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Almost always yes — retaining existing structure saves ~60–80% of substructure + frame embodied carbon. Even deep retrofit beats demolition + rebuild on whole-life carbon if existing structure sound. RIBA + LETI guidance: retain + retrofit before demolish + rebuild.

Does timber frame really beat steel?

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For typical extension spans (<5m), yes — timber I-joist or LVL 80–150 kgCO2e/m³ vs structural steel 1,540 kgCO2e/m³. For longer spans + concentrated loads, steel still needed but minimise tonnage (cantilever raft instead of concrete pile cap; smaller beam where calc permits).

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