Limiting Thermal Bridging and Air Infiltration

Introduction

This guide to Acceptable Construction Details (ACDs) is intended to help the construction industry achieve the performance standards in the Technical Guidance Document (TGD) to Part L of the Building Regulations - Conservation of Fuel and Energy - Dwellings. The 2021 edition of the ACDs updates drawings to take account of internal insulation which was previously provided for in text of 2011 ACDs and some editorial updates. It does not change the thermal performance of the details from the 2011 edition.

This Guide

This guide focuses on issues concerning thermal bridging and airtightness. The guide is presented in two parts.

PART 1

Part 1 discusses the general theory of insulation continuity and airtightness in construction. A common approach to the design, construction and testing methodology is considered and suggestions are made for the general improvement of the process. The use of the Acceptable Construction Details in the context of Technical Guidance Document L is discussed. Construction detailing can create opportunities for increased design flexibility and overall energy efficiency. The increasing significance of detailing and detail thermal performance are discussed. Finally, an overview of "How to achieve good performance in thermal bridging and air infiltration" is presented.

PART 2

Part 2 of this guide is in seven sections and provides large scale indicative detail drawings of thermal insulation and airtightness provisions for specific construction interfaces. The details are accompanied by comments and checklists to assist the designer and builder to achieve the guidance provided in Technical Guidance Document (TGD) L 2021 Conservation of Fuel and Energy in Dwellings to Part L of the Building Regulations at various stages throughout construction. These checklists will also be of assistance to Building Control Authorities.

Application of Acceptable Details

The guide and the ACDs have mainly been conceived in relation to the construction of new dwellings, they may also be used for alteration and extension of dwellings, where appropriate. They are also valid in non-domestic buildings of similar construction. Use of the ACDs during construction will enable the designer/builder to demonstrate that provision has been made to eliminate all reasonably avoidable thermal bridges in the insulation layers (so far as the details apply). As the ACDs focus mainly on Part L issues, further specific guidance relating to other parts of the building regulations may be found in each of the Technical Guidance Documents A-M.

Acknowledgements

The Department would like to thank all those involved in the development of these
Acceptable Construction Details. The Department of Housing, Local Government and Heritage would like to acknowledge the following for the use of photographs in this document:

 Proclima

 Viking House

 Moyisover

 Mark Stephens Architects

 Horizon Offsite Ltd