Accredited construction details ACDs

Accredited construction details (ACDs) are a set of standardised junction details developed in 2002 that can be followed to ‘design out’ thermal bridges in compliance with the energy efficiency requirements (Part L) of the Building Regulations.

A thermal bridge (sometimes referred to as a cold bridge or thermal bypass) describes a situation in which there is a direct connection between the inside and outside of a building through one or more elements that are more thermally conductive than the rest of the building envelope. As a result, there can be wasteful heat transfer across those elements, and the internal surface temperature will be different from other, better insulated internal surfaces which can result in condensation.

The ACDs provide a description of how to construct standard details. They focus on insulation continuity and air tightness and provide checklists which can be used by designers, constructors and building control bodies to ensure provision has been made to eliminate all reasonably avoidable thermal bridges.

While they have primarily been developed in relation to the construction, alteration and extension of dwellings, they may also be valid for buildings other than dwellings where the construction details are similar.

The details are grouped by generic construction type:

• Steel frame details;
• Timber frame details;
• Masonry cavity wall insulation details;
• Internal walls, and
• Masonry external wall insulation details.

The ACDs have now been archived, and their status is not clear, however, they are still available to download from the national archive.

Further accredited details are available for Scotland 2015 and Northern Ireland 2015.

NB Part L 2021 Where to start, A guide for housebuilders and their advisors, Masonry construction, published by the Future Homes Hub in June 2022, states: ‘Typical construction details which were published in 2007 by the Department for Communities and Local Government to address issues with continuity of thermal and airtightness layers in construction. While ACDs are largely out of date, they have not been withdrawn and are still available for use.’

[edit] Related articles on Designing Buildings

• Air tightness in buildings.
• Approved document L.
• Cold bridge.
• Condensation.
• Conduction.
• Insulation.
• Robust details certification scheme.
• Thermal bridging.
• Thermal comfort.
• U-values.