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Carbon benefits from the new Part L
Dwelling type	CO₂ saving per year per home (tonnes)	Carbon saving per year per home (tonnes)	Number of homes built per year	Annual national carbon saving in 2010 (tonnes)
Flats and maisonettes	1.2	0.40	37,600	75,200
Mid-terrace	1.0	0.33	25,300	42,167
Semi-detached houses and bungalows	1.3	0.43	23,100	50,050
Detached houses and bungalows	1.5	0.50	58,500	146,250
Total per year in 2010	Ìý	Ìý	Ìý	313,667
Source: Proposals for Amending Part L, July 2004

The cost of implementing the changes
Dwelling type	Extra cost per unit (Â£)
Flats and maisonettes	323
Mid-terrace	372
Semi-detached houses and bungalows	574
Detached houses and bungalows	1170
Source: Proposals for Amending Part L, July 2004

Worst acceptable U-values (W/m²K)
Element	Area-weighted average value for all elements of the type	Individual element value
Wall	0.35	0.45
Floor	0.25	0.45
Roof	0.25	0.35
Windows, doors, roof windows and rooflights	2.2	3.3
Source: Proposals for Amending Part L, July 2004