Tables 3-5:Typical insulation levels required to satisfy the Best Practice specification for home extensions

 Figures underlined indicate where the required performance is higher than the basic specification. These examples show the levels of insulation and boiler efficiency required to satisfy the Carbon Index targets.

Table 3:Two-bedroom flat – floor area 61m2

Heating Fuel / Natural Gas / Oil / LPG / Electricity

Carbon index 8.6 / 7.4 / 8.6 / 6.8

U-value (W/m2k)

- roof * 0.13 / 0.13 / 0.13 / 0.13

- walls 0.25 / 0.25 / 0.25 / 0.25

- floor* 0.20 / 0.20 / 0.10 / 0.20

- windows, doors, rooflights 1.8 / 1.8 / 1.8 / 1.8

Boiler efficiency 86% / 89% / 86% / N/A

(combi boiler assumed) (combi boiler assumed) (storage heaters)

* for ground and top floor flats as applicable

Table 4: Semi-detached house – floor area 89m2

Heating Fuel / Natural Gas / Oil LPG / Electricity

Carbon index 8.6 / 7.4 / 8.6 / 6.8

U-value (W/m2k)

- roof 0.13 / 0.13 / 0.08 / 0.08

- walls 0.25 / 0.25 / 0.15 / 0.20

- floor 0.20 / 0.20 / 0.10 / 0.15

- windows, doors, rooflights 1.8 / 1.8 / 1.5 / 1.5

Boiler efficiency 86% / 89% / 93.3% / N/A (storage heaters)

Table 5: Detached house – floor area 104m2

Heating Fuel / Natural Gas / Oil LPG* / Electricity

Carbon index 8.6 / 7.4 / 8.6 / 6.8

U-value (W/m2k)

- roof 0.1 / 0.1 / 0.08 / 0.08

- walls 0.2 / 0.22 / 0.15 / 0.15

- floor 0.18 / 0.18 / 0.10 / 0.15

- windows, doors, rooflights 1.8 / 1.8 / 1.5 / 1.5

Boiler efficiency 86% / 89% / 93.3% / N/A (storage heaters)

* mechanical ventilation with heat recovery also assumed here