Is CIBSE Guide A Up to Date? Quick Reference for 2026

CIBSE Guide A is the foundation standard for almost every MEP engineer in the UK. If you're working on environmental design, ventilation rates, internal temperatures, or thermal comfort, you're referencing Guide A. Here's the current status.

Current edition

What Guide A covers

Section 1 covers environmental criteria for design — internal temperatures, ventilation rates, noise criteria, and lighting levels. This is where you find L/s per person rates for different space types, acceptable temperature ranges for offices, retail, and residential spaces, and the baseline criteria that feed into almost every mechanical design calculation. If you're setting up design conditions for a project, Section 1 is your starting point.

Section 5 deals with thermal design and plant sizing — thermal transmittance, heat loss calculations, and steady-state methods. U-values, fabric heat loss coefficients, and the fundamental basis for EN 12831 heating load calculations all sit here. This section is essential for anyone sizing heating systems or calculating building heat losses.

Section 6 provides internal heat gain data — occupant heat gains by activity level, lighting gains by fitting type, and equipment heat gains for common office and commercial equipment. These are the standard values that most engineers use for cooling load estimates, and they form the basis for sizing cooling plant and air handling systems.

What changed since the 2006 edition

The 2015 edition was a significant update. Overheating criteria were revised to align with the TM52 adaptive comfort methodology, which replaced the simpler static threshold approach. Ventilation rates were updated to reflect current research, and solar gain data was refreshed. References to Building Regulations were updated to Part L 2013 and Part F 2010 (both now superseded by the 2021/2022 editions).

The 2021 digital amendments updated some reference values and cross-references but did not change the fundamental calculation methods or design criteria. The core methodology in the 2015 edition remains the current approach.

What to watch for

CIBSE periodically updates its guides, and there is no confirmed publication date for a new edition of Guide A. However, when Part L and Part F were updated in 2021 and 2022 respectively, some cross-references in Guide A became slightly outdated. Always verify that the Building Regulations edition you're working to matches the references in Guide A — and where they differ, the Building Regulations take precedence.

For overheating assessments, Guide A defers to TM52 for the detailed methodology. Make sure you're using TM52 alongside Guide A when assessing overheating risk, particularly on school and residential projects where BB101 or the overheating provisions in Part O apply.

For ventilation rates, be aware that BB101 and Part F may set higher minimum rates than Guide A suggests for specific building types. Guide A provides general design guidance, but project-specific standards (like BB101 for schools or HTM 03-01 for healthcare) will often have stricter requirements. Always cross-reference against the applicable building-type standard.

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