SmallCarbon®
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Methodology

How SmallCarbon® works out the carbon of a building, in plain words.

A building’s whole life

Carbon is counted stage by stage. Choose how much of the life to count.

Example: a primary school extension
312

kgCO₂e/m² · A1-A5

Everything up to the day the building is finished.

Product
Making the materials and products.

A1-A3

Counted
Construction
Bringing them to site and building with them.

A4 and A5

Counted
Upkeep
Maintaining, repairing and replacing parts.

B1 to B5

Not counted
Energy and water
The energy and water the building uses each year.

B6 and B7

Not counted
End of life
Taking the building down and treating what it is made of.

C1 to C4

Not counted
Beyond the building’s life
What the next building gains when materials are reused or recycled.

D

Reported apart

How a figure is made

A quantity, times the carbon of one unit of it.

One row of a project
External wall, timber frame. Change the area.
m²

Carbon of one m² of it

22.1kgCO₂e/m²

Carbon of the row

5,304kgCO₂e

The product stage of the row. The same area then runs through every other stage: transport, waste on site, replacement and the end of its life.

60 years of use

Parts wear out and are replaced. The electricity the building uses gets cleaner.

Parts are replaced
Each time a part reaches the end of its life, the carbon of a new one is counted.

  • Structure

    Lasts 60 years. Never replaced.

  • Rain screen cladding

    Lasts 30 years. Replaced once.

  • Carpet

    Lasts 7 years. Replaced 8 times.

  • Paint

    Lasts 5 years. Replaced 11 times.

Completion

60 years

Electricity gets cleaner
Grams of carbon dioxide for each kWh generated, to 2050
  • The grid getting cleaner, as NESO expects
  • The grid as it is today

Carbon stored in timber

Counted when it is stored and again when it is released, and never hidden inside another figure.

  1. Taken up

    A tree takes carbon out of the air as it grows.

  2. Stored

    Built in, the timber holds it. It counts as carbon removed when the building is made.

  3. Released

    The same carbon counts as released when the building is taken apart.

−62kgCO₂e/m²

An example: the carbon a timber frame stores. Upfront carbon is shown without it, with the stored carbon beside it, always in green.

How sure the figure is

An early design is less certain, so the figure a version reports carries a larger allowance, as RICS sets.

RIBA Stages 0 to 2
+15%

Strategic definition to concept design

RIBA Stages 3 to 5
+6%

Spatial coordination to manufacturing and construction

RIBA Stages 6 and 7
None

Handover to use

From Stage 3 the quality of the carbon data and of the quantities is scored and added too. The figure as calculated is always a choice away.

Where the figures come from

The standard

RICS, Whole life carbon assessment for the built environment, 2nd edition, version 3 (August 2024)

Materials

Circular Ecology’s carbon database, with manufacturers’ and sector EPDs.

Energy, fuel and water

UK Government GHG Conversion Factors for Company Reporting 2026 (DESNZ), full set, version 1.0

The grid’s future

NESO Future Energy Scenarios 2025, Falling Behind

Checked

The calculation is tested against RICS’s own worked examples.

The full method statement
Every module, formula and table, for assessors and auditors.