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Read our policy.

Area weighted average U-value standards (W/m²K)
ElementArea weighted average (W/m²K)*
Wall0.35
Floor0.25
Roof0.25
Windows, rooflights and curtain walls2.20
Pedestrian doors2.20
Vehicle access doors1.50
Roof ventilators and smoke vents 6.00
* Individual elements are subject to an overall limiting value over and above the area weighted average
Comparative design standards for thermal performance
ElementUnitTypical standardPassivhaus standard
Heating demandBTU/ft²/heating degree day 5-151
Air leakageVolume/hour10.6
Heating loadKWh/m²/annum15015
Wall(W/m²K)0.350.15
Window(W/m²K) 2.200.80
Extra-over costs for thermal performance enhancements to glazing
ComponentUnitExtra-over cost
Triple-glazed panel with krypton gas£75
Interpane gas to double-glazed unit (argon)Nil
Interpane gas to double glazed unit (krypton)£15
Low-e glass coatingNil
09 - Comparative capital cost and performance of thermal insulants
InsulantClassThickness (mm)LocationCost (£/m²)Thermal conductivity W/mKProperties
ÌýThermalDurability
Rock woolMineral fibre100Pitched roof/wall4-60.033 - 0.044XXXX
ÌýÌý170Pitched roof10-140.033 - 0.044XXXX
Glass woolMineral fibre100Pitched roof7-90.033 - 0.044XXXX
ÌýÌý150Wall8-100.033 - 0.044XXXX
Rigid urethane foam (PUR)Plastic cellularÌýWall11-130.022 - 0.028XXXXX
PolyisocyanuratePlastic cellular100Pitched Roof8-100.029 - 0.031XXXXXX
ÌýÌý60 (tapered)Flat roof35-450.029 - 0.031XXXXXX
Expanded Polysterene (EPS)Plastic cellular75Wall8-100.032 - 0.040XXXXX
ÌýÌý100Pitched roof9-110.032 - 0.040XXXXX
Extruded polystyrene (XPS)Plastic cellular135Flat roof25-320.028 - 0.036XXXXXX
ÌýÌý50Below-ground walls23-260.028 - 0.036XXXXXX
Cellulose fibrePlant/animal fibre100Wall9-110.036 - 0.040XXX
WoolPlant/animal fibre100Wall13-150.037 - 0.040XXXX