Sustainability: Thermal insulation | Features

Area weighted average U-value standards (W/m²K)
Element	Area weighted average (W/m²K)*
Wall	0.35
Floor	0.25
Roof	0.25
Windows, rooflights and curtain walls	2.20
Pedestrian doors	2.20
Vehicle access doors	1.50
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
Element	Unit	Typical standard	Passivhaus standard
Heating demand	BTU/ft²/heating degree day	5-15	1
Air leakage	Volume/hour	1	0.6
Heating load	KWh/m²/annum	150	15
Wall	(W/m²K)	0.35	0.15
Window	(W/m²K)	2.20	0.80

Extra-over costs for thermal performance enhancements to glazing
Component	Unit	Extra-over cost
Triple-glazed panel with krypton gas	m²	£75
Interpane gas to double-glazed unit (argon)	m²	Nil
Interpane gas to double glazed unit (krypton)	m²	£15
Low-e glass coating	m²	Nil

09 - Comparative capital cost and performance of thermal insulants
Insulant	Class	Thickness (mm)	Location	Cost (£/m²)	Thermal conductivity W/mK	Properties
						Thermal	Durability
Rock wool	Mineral fibre	100	Pitched roof/wall	4-6	0.033 - 0.044	XX	XX
		170	Pitched roof	10-14	0.033 - 0.044	XX	XX
Glass wool	Mineral fibre	100	Pitched roof	7-9	0.033 - 0.044	XX	XX
		150	Wall	8-10	0.033 - 0.044	XX	XX
Rigid urethane foam (PUR)	Plastic cellular		Wall	11-13	0.022 - 0.028	XXX	XX
Polyisocyanurate	Plastic cellular	100	Pitched Roof	8-10	0.029 - 0.031	XXX	XXX
		60 (tapered)	Flat roof	35-45	0.029 - 0.031	XXX	XXX
Expanded Polysterene (EPS)	Plastic cellular	75	Wall	8-10	0.032 - 0.040	XX	XXX
		100	Pitched roof	9-11	0.032 - 0.040	XX	XXX
Extruded polystyrene (XPS)	Plastic cellular	135	Flat roof	25-32	0.028 - 0.036	XXX	XXX
		50	Below-ground walls	23-26	0.028 - 0.036	XXX	XXX
Cellulose fibre	Plant/animal fibre	100	Wall	9-11	0.036 - 0.040	XX	X
Wool	Plant/animal fibre	100	Wall	13-15	0.037 - 0.040	XX	XX