INTRODUCTION
This section shows appropriate details for light steel frame construction. The Introduction document "Limiting Thermal Bridging and Air Infiltration Acceptable Construction Details" provides practical information with regards to implementation of these details onsite. This guide should be read in conjunction with these details. Details are given for junctions with a range of roof, ground floor and internal floor types, as well as at external wall opes. The details within this section are valid for a range of steel frame wall thicknesses.
With steel frame, some insulation must be placed outside the frame to provide a thermal break and avoid condensation. Warm frame construction is where all the insulation is outside the frame. Hybrid construction is where insulation is included both outside the steel structure and in between the steel components. At least 33% of the thermal resistance should be provided outside the steel. Where compressible insulation is installed between studs in addition to rigid board insulation over, it should be tightly packed and be in direct contact with the rigid board. Take care to ensure compressible insulation is maintained above dewpoint temperature. With hybrid construction, the system manufacturer should provide a condensation risk analysis (in accordance with Technical Guidance Document L, Appendix B) to ensure there is no risk of interstitial condensation. An internal vapour control layer is
generally required. The details show warm frame construction but apply equally to hybrid construction.
Insulation thicknesses have not been provided as these depend on the thermal properties of the materials chosen together with the proposed U-value. It is important to choose appropriate tightly fitting materials. Generally, a rigid insulation material, which acts as an insulated sheathing board, is required outside the frame.
Details show a masonry outer leaf for simplification. The details are also appropriate for a range of other claddings subject to suitable detailing. Further variables are insulation and sheathing types, and internal lining type and thickness. All external cladding systems should be "proper materials" as defined in Part D.
These diagrams illustrate good practice for design and construction of interfaces only in respect to ensuring thermal performance and air barrier continuity. Other issues are not considered fully. The guidance must be implemented with due regard to all other Building Regulations requirements. All materials and workmanship to be installed to Technical Guidance Document D "Materials and Workmanship."
Where these details are used for the Target U-values and constructions described in Table D5 of TGD L 2021 the psi values published in Table D5 may be used to calculate the actual Thermal Bridging heat loss for the key thermal bridging junctions in that dwelling.
Technical Guidance Document B and Supplementary Guidance to TGD B provides guidance in relation to the provision of cavity barriers in air cavities, cavity barriers within combustible insulation layers and fire protection of structural elements.
The 2021 edition of the ACDs updates the drawings to take account of industry practice. The performance requirements remain the same as for the 2011 edition.
