What the L is going on? | Features

Current thermal efficiency requirement for house elements
Exposed element	U-value with low-energy rating (W/m2 °C)	U-value with high-energy rating (W/m2 °C)
Roof	0.2	0.25
Wall	0.45	0.45
Exposed and ground floor	0.35	0.45
Semi-exposed wall and floor	0.6	0.6
Windows, doors and rooflights	0.3	3.3

Proposed thermal efficiency requirement for house elements 2001-2003
	2001	2003	2001	2003
Exposed element	U-value with efficient heating (W/m2 °C)		U-value with inefficient heating (W/m2 °C)
Pitched roof (with insulation between rafters)	0.25	0.2	0.2	0.15
Pitched roof (with insulation between joists)	0.2	0.16	0.16	0.15
Flat roof	0.25	0.25	0.2	0.2
Wall	0.35	0.3	0.3	0.25
Floor	0.3	0.25	0.25	0.22
Windows, doors and rooflights (overall average)	2.2	2	2	1.8
source: Working group document