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) Airtightness Airtightness in new dwellings 4.20 The minimum standard for air permeability of a new dwelling is given in Table 4.1. When carrying out work in new dwellings, care should be taken to reduce unwanted heat loss through air infiltration. 4.21 To ensure airtightness in new dwellings, all of the following apply. a. Drawings: all relevant drawings should be provided to clearly identify the position, continuity and extent of the air barrier. Drawings should be reviewed by the designer and installer and should include specifications for key materials. b. Incoming services: ducts, and cables wherever possible, should be grouped to minimise how often the air barrier is penetrated, while ensuring sufficient space to allow adequate screed flow between ducts. (Use temporary supports for services during floor works.) Grommets or flexible collars should be used around incoming services and sealed to the air barrier with air-sealing tape or sealant. c. Internal building services: where services penetrate the air barrier, holes should be as small as possible and should be core drilled to limit damage. The penetrating services should be sealed to the air barrier using proprietary grommets or collars with air-sealing tape or sealant. Where membranes are penetrated, careful detailing should be used to achieve a robust and durable seal at these penetrations. d. Structural penetrations need to be effectively sealed for airtightness. Timber joist hangers should be considered as an alternative to penetrating through the inner leaf. e. Cavity walls: the inner block leaf mortar joint should be fully filled and pointed within the cavity. Where dense aggregate blocks have been used, plaster, parge coat or liquid membranes should be applied internally to reduce air permeability. Internal plasterboard linings are not appropriate for use as an air barrier solution. f. Timber frame: the vapour control layer should overlap at seams and junctions and be taped where it forms the airtightness barrier. Any damage, such as tears, should be repaired before boarding. Where sheathing board forms the air barrier, air-sealing tape should be applied at junctions and edges. g. Fixings: care should be taken to ensure that fixings do not damage the airtightness barrier. h. Windows and doors: to ensure continuity of the air barrier, window and door units should connect to the primary air barrier and window and door frames should be taped to surrounding structural openings, using air sealing tape. Compressible seals or gun sealant may be used to supplement taping. i. Loft hatches: where the roof is insulated at ceiling level, hatches should be suitably designed and installed to ensure optimum airtightness. 4.22 To avoid air movement within thermal elements, either of the following measures should be implemented. a. The insulation layer should abut the air barrier at all points in the building envelope. b. The space between the air barrier and the insulation layer should be filled with solid material. 30 Approved Document L Volume 1, 2021 edition Building Regulations 2010 O N L I N E V E R S I O N