U-value upgrading standards for thermal elements

Element(1) U-value (W/m2.K)(2) (a) Threshold (b) Upgraded Cavity wall – cavity insulation(3) 0.70 0.55 Wall – external or internal insulation(4) 0.70 0.30 Pitched roof – insulation at ceiling level 0.35 0.16 Pitched roof – insulation at or between rafters(5) 0.35 0.18 Flat roof or roof with integral insulation(6) 0.35 0.18 Floors(7)(8) 0.70 0.25 Notes: (1) "Roof" includes the roof parts of dormer windows, and "Wall" includes the wall parts (dormer cheeks) of dormer windows. (2) Area-weighted average value. (3) This applies only in the case of a wall suitable for the installation of cavity insulation. Where this is not the case it should be treated as for "Wall – external or internal insulation". (4) A lesser provision may be appropriate where meeting such a standard would result in a reduction of more than 5% in the internal floor area of the room bounded by the wall. (5) A lesser provision may be appropriate where meeting such a standard would create limitations on head room. In such cases, the depth of the insulation plus any required air gap should be at least the depth of the rafters, and the thermal performance of the chosen insulant should be such as to achieve the best practicable U-value. (6) A lesser provision may be appropriate if there are particular problems associated with the loadbearing capacity of the frame or upstand height. (7) The U-value of the floor of an extension can be calculated using the exposed perimeter and floor area of the whole enlarged building. (8) A lesser provision may be appropriate where meeting such a standard would create significant problems in relation to adjoining floor levels.