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Embodied carbon is the greenhouse gas emitted to make, transport, install, maintain and eventually dispose of a building's materials. It is measured in kilograms of carbon dioxide equivalent (kgCO₂e). For many new buildings it is as large as the carbon from decades of operation, and almost all of it is fixed by design decisions: frame, foundations, façade.
The calculation is simple: for each material, multiply its quantity (m³, m², tonnes) by its carbon factor (kgCO₂e per unit), then add them up. Factors come from environmental product declarations (EPDs) for specific products, or from generic databases. The model supplies the quantities.
At stage 4 the sustainability consultant asks for an embodied carbon figure. The model is detailed, but a third of its elements have generic materials. After two weeks of mapping, the figure is 20% over the client's target. The frame is already designed and coordinated; all that can change is the finishes.
At concept, the design team compares a concrete frame and a timber hybrid with rough quantities from massing models. The hybrid saves a third of the frame's carbon. The choice is made then, and materials are named properly from the start, so each later stage's figure comes from the model in a day.
From model to carbon figure
| Step | What to check |
|---|---|
| Scope | Which elements (frame, foundations, envelope, finishes, services) and which life stages |
| Quantities | Taken by material, in the units the factors use |
| Materials | Every element has a real material, no "Default" or "Generic" |
| Factors | Each material mapped to a factor, with its source |
| Result | Total and breakdown by element group, with the model version |
The clinic's frame has 400 m³ of concrete (300 kgCO₂e/m³) and 40 t of reinforcing steel (1,200 kgCO₂e/t).
Carbon of the frame
400 m³ of concrete at 300 kgCO₂e/m³ and 40 t of reinforcing steel at 1,200 kgCO₂e/t. What is the frame’s embodied carbon, in tonnes CO₂e?
Key takeaways
- Embodied carbon = quantity of each material × its carbon factor, summed over the building.
- The model's quantities are only useful if each element has a material that maps to a factor.
- Early, rough figures change designs; late, precise figures only report them.
- Always state the scope (which elements, which life stages) and the source of the factors.
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Related tool
Quantities and costs on the 3D model: colour by cost, find what can't be measured, see each revision's change and when the money is spent.
Open Quantity Take-off and 5D →