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U-value Requirements

The U-value of a building element (i.e Walls, Floors or Roofs) is a measure of the thermal efficiency or heat loss through that element.The lower the U-value the better the thermeal efficiency of the element.

The U-value requirments for Building elements are outlined in Part L: of The Building Regulations 2007. To view this document click on the following link: For new dwellings the elemential U-value is outlinned in the table below.

Table 5

Maximum average area-weighted elemental U-value (W/m2K)1.2

Column 1
Fabric Elements
Column 2
Column 3 Material Alterations or Material hange of Use
Pitched roof
* Insulation at ceilinga 0.16 0.35
*Insulation on slope 0.20  
Flat roof 0.25  
Walls 0.27 0.60
Ground Floors3 0.25  
Other Exposed Floors3 0.25 0.60
External doors, windows and rooflights 2.004 2.004
1. The U-value includes the effect of unheated voids or other spaces.
2. For material alterations, the U-value relate to the new works.
3. For Insulation of ground floors and exposed floors incorporating underfloor heating.
4. For extensions and material change of use, windows, doors and rooflights should have maximum U-value of 2.0W/m2K and maximum opening aea of 25% of floor area. However areas and U-values may be varied.

The above Table 5 has been extracted from the Building Regulations 2007 Part L Technical Guidance Document.