Conservation of fuel and power: Approved Document L, Volume 2 — Buildings other than dwellings

O N L I N E V E R S I O N L1(a) Table 4.2 L imiting U-values for existing elements in existing buildings Element U-value(1) W/(m2·K) (a) Threshold (b) Improved Pitched roof – insulation at ceiling level(2) 0.35 0.16 Pitched roof – insulation at rafter level(2)(3) 0.35 0.18 Flat roof or roof with integral insulation(2)(4) 0.35 0.18 Wall – cavity insulation(2)(5) 0.70 0.55 Wall – external or internal insulation(2)(6) 0.70 0.30 Floors(7)(8) 0.70 0.25 NOTES: 1. Area-weighted average values. 2. For dormer windows, ‘roof’ includes the roof parts of the window and ‘wall’ includes the wall parts (cheeks). 3. If meeting such a standard would limit head room, a lesser standard may be appropriate. In such cases, both of the following should be achieved. a. The depth of the insulation plus any required air gap should be at least to the depth of the rafters. b. The insulant should be chosen to achieve the lowest practicable U-value. 4. If there are problems with the load-bearing capacity of the frame or height of the upstand, for a flat roof or roof with integral insulation, a lesser standard may be appropriate. 5. This applies only to a wall suitable for cavity insulation. Where this is not the case, it should be treated as ‘wall – external or internal insulation’. 6. If meeting such a standard would reduce the internal floor area of the room bounded by the wall by more than 5%, a lesser standard may be appropriate. 7. The U-value of the floor of an extension may be calculated using the exposed perimeter and floor area of either the whole enlarged building or the extension alone. 8. If meeting such a standard would create significant problems in relation to adjoining floor levels, a lesser standard may be appropriate. Continuity of insulation 4.9 In new and existing buildings both of the following should apply. a. The insulation should be reasonably continuous across newly built elements. b. Thermal bridging, including at the party wall, should be reasonably limited. NOTE: Any solution to edge sealing or thermal bridging in new buildings should take particular account of Part E of the Building Regulations. 4.10 To avoid air movement within thermal elements in new and existing buildings, either of the following measures should be implemented. a. The insulation layer should abut the air barrier at all points across newly built elements. b. The space between the air barrier and the insulation layer should be filled with solid material. 27 Building Regulations 2010 Approved Document L Volume 2, 2021 edition O N L I N E V E R S I O N