The U-value assumed for a pitched roof with an insulated ceiling should, where possible, be based on the observed thickness of the loft insulation (mineral wool) according to Table 2.16 below. Table 2.7 sets out the age-band ranges
| Insulation thickness (mm) | Assumed roof U-value (W/m²K) |
|---|---|
| None | 2.3 |
| 12 | 1.5 |
| 25 | 1.1 |
| 50 | 0.68 |
| 75 | 0.5 |
| 100 | 0.4 |
| 150 | 0.26 |
| 200 | 0.2 |
| 250 | 0.16 |
| >= 300 | 0.13 |
If the insulation thickness is not known, the U-value should be taken from Table S5. Where there are loft areas with different insulation thicknesses, enter each of these areas as separate roofs in DEAP or base the U-values on area weighted thickness of insulation.
In the case of rafter or flat roof insulation observed onsite with indicators according to the DEAP Survey Guide, table S3c may be used to select the default U-value.
| Age band | Assumed roof U-value (W/m²K) (applies to all roof types). |
|---|---|
| A, B, C, D, E | 2.3 |
| F, G | 0.49 |
| H | 0.40 |
| I | 0.36 |
| J | 0.25 |
| K | 0.22 |
| L | 0.20 |
Some of the U-values in Table S5 differ from those for roofs in Table S2. Table S5 U-values are based on insulation thicknesses stated in the regulations applicable to each age band and current U-value calculation methods.
Where the BER assessor comes across information2 indicating that roofs have been upgraded but appropriate supporting documentation is not available, they should refer to guidance in S6.1 U-values of walls and to the Acceptable verification indicators listed in Appendix B of the DEAP survey guide.