U-Value HistoryThe u-value limits introduced in 1965 were:

1.7 for walls1.4 for roofs

These were tightened in 1976 to:

1.0 for exposed walls, floors and non-solid ground and exposed floors1.7 for semi-exposed walls1.8 average for walls and windows combined0.6 for roofs

1985 saw the second tightening of these limits, to:

0.6 for exposed walls, floors and ground floors0.35 for roofs

These limits were reduced again in 1990:

0.45 for exposed walls, floors and ground floors0.6 for semi-exposed walls0.25 for roofsplus a requirement that the area of windows should not be more than 15% of the floor area.

In the 1995 Building Regulations, insulation standards were cut to the following U-values:

0.45 for exposed walls, floors and ground floors0.6 for semi-exposed walls and floors0.25 for roofsthe limit on window area was raised to 22.5%

The 2002 regulations reduced the U-values, and made additional elements of the building fabricsubject to control. Although there was in practice considerable flexibility and the ability to 'trade off'reductions in one are for increases in another, the 'target' limits became:

0.35 for walls0.25 for floors0.20 or 0.25 for pitched roofs (depending on the construction)0.16 for flat roofs2.2 for metal framed doors and windows2.0 for other doors and windowsthe limit on window area was raised again to 25%

YEAR 1965 1976 1985 1990 1995 2002 2006' 20102

FABRIC U-Value W/m2.K

Walls 1.7 1.0 0.6 0.45 0.45 0.35 0.35 0.35

Floors 1.0 0.6 0.45 0.45 0.25 0.25 0.25

Pitched Roof 1.4 0.6 0.35 0.25 0.25 0.25 0.25 0.25

Flat Roof 0.6 0.35 0.25 0.25 0.16 0.25 0.25

Windows metal 2.2 2.2 2.2

Windows all other 2.0 2.2 2.2

Window Area 15% 22.5% 25%

Pedestrian Door 2.2

Vehicle Doors 1.5 1.5

Entrance Doors 6.0 3.5

Air Permeability3 10 10

Notes1. 2006 values are area-weighted average limiting standards (Part L2A). SBEM calculation

required.2. 2010 values are limiting fabric parameters (Part L2A). SBEM calculation required.3. Air permeability units m3/(h.m2) @ 50Pa.