Cost Savings Tables

Assumptions used in Calculations (follow the links for further information about each topic)

• Internal temperature 18°C average

• External temperature 5°C average

• Gas boiler (75% efficient)

• 30% of heat lost through ventilation. This may be less if the house is well draught-proofed.

• Uninsulated Property (typical of pre-1900 homes)

  • Solid brick external wall (U-value 2.7 W/mK)

  • Uninsulated suspended timber floor (U-value 1.3 W/mK)

  • Roof with no loft insulation (U-value 2.3 W/mK)

  • Single-glazed windows (U-value 5.6 W/mK)

• Moderately-Insulated Property (typical of mid-20th century homes)

  • Unfilled cavity wall (U-value 1.0 W/mK)

  • Solid ground floor (U-value 1.0 W/mK)

  • Roof with 100mm loft insulation (U-value 0.4 W/mK)

  • Double-glazed windows (U-value 2.8 W/mK)

• Well-Insulated Property (typical of late-20th century homes)

  • Insulated cavity wall (U-value = 0.45 W/mK)

  • Insulated floor (U-value 0.18 W/mK)

  • 200mm loft insulation (U-value 0.2 W/mK)

  • Double-glazed windows (U-value 2.8 W/mK)

• Properties are assumed to lose heat through external walls only (i.e. a wall to an adjoining property is not included on the assumption that it is also heated)

• All properties are assumed to lose heat through their floor and roof (this may not be the case for a flat with other heated flats above and/or below).

• Flats and terraced houses are assumed to lose heat through two external walls only.

• Semi-detached houses are assumed to lose heat through three external walls.

• Bungalows and detached houses are assumed to lose heat through four external walls.