L3 New dwellings
Average area weighted elemental U-value
Table 1 Maximum elemental U-value (W/m2K)1,2
| Fabric elements | Area weighted average elemental U-value (Um) | Average elemental U-value - individual element or section of element |
Roofs Pitched roofs -Insulation at ceiling -Insulation on slope Flat roof |
0.16 0.20 0.22 |
0.3
|
| Walls | 0.27 | 0.6 |
| Ground floors3 | 0.25 | 0.6 |
| Other exposed floors3 | 0.25 | 0.6 |
| External doors, windows and rooflights | 2.004 | 3.0 |
Acceptable thermal envelope levels are specified in terms of average area-weighted U-value (Um) in Table 1(Column 2)
These values can be relaxed for individual elements or parts of elements where considered necessary for design or elements or parts of elements are specified in Column 3 of Table 1.
Where this relaxation is availed of, the average area-weighted values given in Column 2 continue to apply and compensatory insulation measures may be necessary for other elements
NOTES
2, The U-value includes the effect of unheated voids or other spaces.
3, For insulation of ground floors and exposed floors incorporating under floor heating, a floor U-value of 0.15 W/m2K should be satisfactory.
4, Windows, doors and roof lights should have maximum U value of 2.0 W/m2K and maximum opening area of 25% of floor area.
| Slab on ground floors Care should be taken to control the risk of thermal bridging at the edges of floors. All slab-on ground floors should be provided with edge insulation to the vertical edge of the slab at all external and internal walls. The insulation should have minimum thermal resistance of 0.7 m²K/W Some large floors may have an acceptable average U-value without the need for added insulation, however, perimeter insulation should always be provided. |
