In Part L 2021 U Values were uprated
Learn more here about the u value changes and new targets. U-values were updated in Conservation of fuel and power: Approved Document L 2021 amendments. This was part of a bigger change, with the introduction of SAP10. Learn more about SAP Calculations by visiting our service page.
What are U-values?
These values represent the thermal transmittance (heat loss) through different building elements, and lower U-values indicate better insulation.
Target values are in place for new-build dwellings and non-dwellings as well as during ‘building work’ or renovations and extensions of existing buildings.
What are the new U Value Targets?
We set out below the minimum U-values for the key building elements in existing dwellings, as
set out in Approved Document L of the Building Regulations – Conservation of fuel and power, Volume 1: Dwellings.
Limiting U-value changes and new targets for new fabric elements in existing dwellings
| Thermal Element | U-value (W/m2K) |
| Roof | 0.15 |
| Wall | 0.18 |
| Floor | 0.18 |
| Window | 1.4 |
| Roof Window | 2.2 |
| Door | 1.4 |
New-build limiting U-value changes and new targets
For new buildings however, targets are tighter
| Thermal Element | U-value (W/m2K) |
| Wall | 0.18 |
| Floor | 0.13 |
| Roof | 0.11 |
| Windows and Doors | 1.2 |
Other Changes and Considerations
In addition air-tightness, thermal bridging and heating efficiencies have been uprated:
- Airtightness – typical maximum result of 5.0
- Thermal bridging – all bridges require measuring however defaults are available (target Y-value of 0.05)
- Heating – if mains gas is to be used, a 92% ErP is required with interlock and compensator.
Offer considerations include:
- Holistic fabric-first approach to becoming net-zero by 2050 (by the implementation of low/zero carbon technologies and onsite generation)
- Appropriate ventilation strategies
- Internal comfort: overheating analysis and background noise levels
- Water usage
- Lighting designs
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