The UK government has set a target in Net Zero Strategy: Build Back Greener to reduce carbon emissions to net zero by 2050. Net zero isn’t straightforward. You need to understand what is meant by operational energy, embodied carbon and whole life carbon.

Operational energy

Operational energy relates to emissions from all energy consumed by a building. It is ‘in-use energy’ and will typically refer to energy used for heating, lighting, cooling and running appliances in a building. If the carbon emissions caused by a building’s operational energy, assessed on an annual basis, are zero or negative it can be said to have net zero operational energy, according to the UK Green Building Council (UKGBC). Such buildings will be highly energy efficient and likely to be making use of on-site or off-site renewable energy sources.

Embodied carbon

Embodied carbon emissions are the total emissions associated with materials and construction processes from ‘cradle to gate’ – manufacturing, transport to site and construction, operation of the building and end of life.

Whole life carbon

This is both embodied carbon and operational energy emissions together, over the life cycle of the building – including its disposal.

The importance of agreeing definitions

Without agreed definitions, performance claims can’t be compared, leaving room for ‘greenwashing’. Many of these working definitions have been agreed by industry working groups in May 2021 and are set out in Improving Consistency in Whole Life Carbon Assessment and Reporting.

The guiding principle for building design and operation should be to use savvy materials and methods for net zero construction and disposal, and minimise emissions, before relying on offsetting measures to achieve net zero.

Further reading:

Operational energy one pager from LETI (The London Energy Transformation Initiative) gives a summary of definitions and recommended design considerations.

LETI’s Embodied Carbon Target Alignment provides datasets for common building typologies and sets out performance level ranges. This carbon rating system can be used to track the urgent performance improvements needed from now until 2030 and it is aligned with the RIBA 2030 Climate Challenge targets.

The LETI embodied carbon primer gives an accessible and practical introduction to the subject.

British Standard BS EN 15978:2011 guides architects through emissions throughout the lifecycle of a building. RICS whole life carbon assessment for the built environment, is based on this standard, and the RIBA whole life carbon assessment for architects guide draws on the RICS methodology.

RIBA’s How software can help you calculate a building’s embodied carbon and Learn to tally up your project’s carbon impact in 15 minutes, discusses tools available.

LETI’s whole life carbon one pager gives a seven-step process for ‘how to’ reduce the whole life carbon of a building.