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) Continuity of insulation 4.14 Gaps in insulation can have a significant impact on heat loss and thermal bypass and create a risk of condensation and mould. The building fabric should be constructed so that the insulation is reasonably continuous across newly built elements. 4.15 To ensure continuity of insulation in new dwellings, all of the following apply. a. Drawings should identify the insulation layer. The designer and installer should review drawings to ensure the insulation layer is continuous, buildable and robust. 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 the guidance in Appendix B. c. Floors and foundations: insulation should be installed tight to the structure, without air gaps between insulation panels and at edges. i. Perimeter insulation should be continuous and have a minimum thickness of 25mm. ii. Moisture-resistant insulation should be fitted below damp-proof course level and extend to the foundation block/structure. d. Windows and doors: should be installed in such a way that the thermal integrity of the insulated plane is maintained. i. Tolerance around a window or door unit and the surrounding opening should be minimal and be in accordance with BS 8213-4. ii. Position: window or door units should be located with an overlap between the inner face of the unit and the inner face of the external leaf – for windows an overlap between 30mm and 50mm, and for doors 50mm – so that the window or door unit is contiguous with the insulation layer of the external wall. iii. Fully insulated and continuous cavity closers should be used, installed tight to the insulation and cavity apertures. For door units, install perimeter insulation within the threshold zone or use a reinforced cavity closure. e. Walls: insulation should be fitted without any air gaps and tight to the structure, cavity closers, lintels and cavity trays. Mortar snots should be removed to ensure a tight fit with the structure and cavities cleared of all debris. Where fire-stopping socks are required, these should fully fill the areas where they are fitted, including at the heads of cavities. f. Roofs: insulation should be installed tight to the structure, without air gaps, and should extend to the wall insulation. For roofs insulated at ceiling level, the long-term protection of the insulation layer should be considered: boarded areas should be provided above the insulation to give access for maintenance. g. Rigid insulation boards: should only be used on flat surfaces. Boards should be fitted to the structure to avoid any gaps between board edges and between the board facings. The use of boards with lapped or tongue and groove edges should be considered. Any unavoidable gaps between boards should be infilled using compressible tape (e.g. for boards within roof rafters) or low expansion foam (e.g. for boards within wall cavities). h. Penetrating elements include steel beams, incoming services, meter boxes and sub-floor vents. Designs should clearly indicate means to limit disruption to the insulation. For recessed meter boxes on the cold side of the construction, insulation should be installed behind the enclosure. For incoming services, insulation should fit tightly around ducts, pipes, etc. Building Regulations 2010 Approved Document L Volume 1, 2021 edition 27 O N L I N E V E R S I O N