TM65 embodied carbon assessment

CIBSE TM65 is a calculation methodology for the embodied carbon of building services equipment — the carbon in making, transporting, maintaining and disposing of the plant, as distinct from the carbon of running it.

It exists because most MEP products have no environmental product declaration. Where a manufacturer has published a verified EPD to BS EN 15804, that figure is used. Where none exists, which is still the common case, TM65 provides a structured estimate from the product's material composition and mass, with an uncertainty factor applied so the answer is honest about being an estimate rather than a measurement.

Building services matter here more than their volume suggests. As fabric improves and operational carbon falls, the proportion of a building's whole life carbon sitting in its plant, pipework, ductwork, cabling and replacement cycles rises — and services are replaced several times over a building's life, so the recurring embodied carbon can exceed the initial figure.

Where a whole life carbon assessment is required — by planning policy, by a funder, by a BREEAM Mat 01 credit, or by a client target such as the RIBA 2030 Climate Challenge or a LETI benchmark — and the MEP contribution has to be quantified rather than excluded with a note.

Also on any project where two plant options are close on capital and operational cost. That is the point at which embodied carbon is the deciding factor rather than a reporting exercise, and it has to be assessed while both options are still live.

Scope first: which systems are included, which life cycle modules are assessed, and what the study is for. An assessment covering only product stage A1 to A3 answers a different question from one covering replacement and end of life, and the two are not comparable.

Verified EPD data is used wherever a manufacturer publishes it. Where it does not exist, the TM65 methodology is applied from the product's own material and mass data, with the uncertainty factor stated rather than quietly absorbed into the total.

Results are reported per system and per life cycle module, not as a single number. A total tells a client nothing they can act on; a breakdown shows which system, and which decision, is worth revisiting.

The assessment is handed over with its assumptions, its data sources and its gaps written down, so it can be updated as the design develops rather than repeated from scratch.