Thermal Bridging
External Building Elements
By default, a thermal bridging allowance will be added to all external building element types to create an effective U-value for calculating fabric heat loss.
The thermal bridging factor will depend on the age band of the main property (not the element itself) and is sourced from RdSAP (9.94) Tables S13.
| Property Age Band | Thermal Bridging Factor (W/m².K) |
|---|---|
| A - I | 0.15 |
| J | 0.11 |
| K onwards | 0.08 |
NOTE
Refer to Appendix S - Reduced Data SAP (9.94) for more information.
Internal Building Elements
By default, a thermal bridging allowance will be added to all internal building elements types to create an effective U-value for calculating fabric heat loss.
The thermal bridging factor will depend on the age band of the property and is derived from CIBSE Domestic Heating Design Guide (2021) Table 3.4.
| Property Age Band | Thermal Bridging Factor (W/m².K) |
|---|---|
| A - K | 0.10 |
| L onwards | 0.05 |
NOTE
Refer to CIBSE Domestic Heating Design Guide (2021) for more information.
Known U-value Elements
When a known U-value is entered into the calculator, it is also possible to specify thermal bridging factor to apply as well.
When not specified, a thermal bridging factor will be applied based on the age band of the property, derived from CIBSE Domestic Heating Design Guide (2021) Table 3.4.
| Property Age Band | Thermal Bridging Factor (W/m².K) |
|---|---|
| A - K | 0.10 |
| L onwards | 0.05 |
NOTE
Refer to CIBSE Domestic Heating Design Guide (2021) for more information.