Conservation of fuel and power: Approved Document L, Volume 1 — Dwellings

O N L I N E V E R S I O N L1(a) Thermal bridging 4.16 Thermal bridges occur when an area of a building has significantly higher heat transfer than the surrounding parts. Breaks in insulation, reduced insulation or more conductive materials can contribute to thermal bridge effects. The building fabric should be constructed so that thermal bridging, including at the party wall, is reasonably limited. Thermal bridging in new dwellings 4.17 To limit thermal bridging in new dwellings, all of the following apply. a. Drawings should be provided for junctions. The designer and installer should review drawings to check that junctions are buildable and to ensure construction sequencing is carefully considered for each detail. Complex details should be avoided wherever possible. b. Before elements are concealed by subsequent work, an on-site audit should be undertaken to confirm that the designed details have been constructed. Photographs of the details should be taken in line with Appendix B. c. Product specification: opportunities should be considered to use products that help to reduce thermal bridges. Options include both of the following. i. Masonry construction: lightweight blockwork in the inner leaf of a cavity wall or both leaves of a party wall can help to reduce thermal transmittance, particularly at junctions, such as the ground floor to wall junction. ii. Timber construction: the use of insulated plasterboard on the inside of the frame can help to reduce bridging at various junctions. d. Product substitution: the products used should be those shown in the original design. If a product is substituted, the revised specification should be reflected in the SAP calculation and report in the Building Regulations England Part L compliance report (BREL report). e. Foundations: wherever possible, blocks below the damp-proof course should be the same as those specified in the design for the above-ground main wall element (in masonry construction). f. Ground floors and external walls: the wall-to-floor junctions should be detailed to achieve continuity of insulation. i. Perimeter floor insulation should abut or extend the full depth of the main floor insulation. ii. Masonry construction: external or cavity wall insulation should extend below the damp- proof course (where applicable) and be at least the equivalent of one full block height (215mm) below the underside of the floor structure/slab and beyond the depth of the floor insulation. iii. Timber construction: insulation between boards/within sheathing should extend to the floor plate. The wall insulation and the floor perimeter insulation should abut. g. Intermediate floors: floor-to-wall junctions should be detailed to ensure that insulation in the external wall is continuous. For a timber frame where the intermediate floor structure breaches the external wall insulation, further insulation – of the same thickness as the insulation used in the external wall – should be included within the depth of the intermediate floor structure. 28 Approved Document L Volume 1, 2021 edition Building Regulations 2010 O N L I N E V E R S I O N