New Build - L1a
Part L 2010 came into force on the 1st October 2010, and is satisfied with the scientific method of SAP 2009. The following limiting fabric rules are mandatory for all new build domestic structures and must be adhered to by all developers, architects and energy assessors.
Limiting U values
These values show the upper limit of what is allowable in new build domestic structures. In order to pass SAP however, these values should be surpassed significantly.
Part L 2010
| Element | U value |
| Wall | 0.3 |
| Party wall | 0.2 |
| Floor | 0.25 |
| Roof | 0.2 |
| Openings | 2 |
| Air permeability | 10 (m3/hm2) |
The recommendations by the same document to pass a SAP assessment are listed below. Care should be taken not to follow this recommendation blindly however as all dwellings will differ. Further guidelines on SAP 2009 solutions have also been listed below - all of which differ slightly to meet the energy model used at the time.
Part L 2010
| Element | Part L recommendation |
| Wall | 0.20 |
| Party wall | 0.2 |
| Floor | 0.2 |
| Roof | 0.13 |
| Window | 1.5 |
| Door | 1.5 |
| Thermal bridging | Y = 0.04 |
| Ventilation rate | 5 (m3/hm2) |
| Mechanical ventilation | - |
| Heating | - |
| Solar hot water | - |
National Energy Services
| Element | NES recommendation |
| Wall | 0.21 |
| Party wall | 0.0 |
| Floor | 0.16 |
| Roof | 0.12 |
| Window | 1.5 |
| Door | 1 |
| Thermal bridging | Y = 0.04 |
| Ventilation rate | 3 (m3/hm2) |
| Mechanical ventilation | Specific fan power 1 w/l/s |
| Heating | Gas Efficiency 90% Load or weather compensator |
| Solar hot water | None |
The Energy Saving Trust
| Element | Energy Saving Trust recommendation |
| Wall | 0.25 |
| Party wall | 0.0 |
| Floor | 0.2 |
| Roof | 0.13 |
| Window | 1.5 |
| Door | 1 |
| Thermal bridging | Y = 0.04 |
| Ventilation rate | 3 (m3/hm2) |
| Mechanical ventilation | Specific fan power 1 w/l/s |
| Heating | Gas Efficiency 90% Load or weather compensator |
| Solar hot water | None |