Part L1A of the Building Regulations
The Standard Assessment Procedure (SAP) is the official English and Welsh system for rating the energy performance of domestic dwellings. The full formal definition of the SAP energy rating is – ‘A number between 1 and 100+ based on the annual space heating, water heating and internal lighting costs per square metre for the property, calculated using standard occupancy and location assumptions and deflated three year average fuel prices’. The SAP energy rating provides the basis for the Energy Performance Certificates (EPCs) required for all new build dwellings at the point of sale, which place the SAP rating on an A-G scale (similar to that used for the energy labels on white goods, such as fridges).
To put the above into more ‘layman-like’ language; The SAP calculates a rating for the annual energy cost for the dwelling in question due to the built structure, it’s heating system, internal lighting and any renewable energy technologies installed. It does not include energy used for cooking and appliances and assumes standard occupancy patterns and a ‘middle of England’ location for calculating the heating requirements over 12 months.
So, if you imagine two identical properties, one built on the south coast of England and the other located on the North Yorkshire Moors, the SAP rating for both properties will be exactly the same, as it would be for any location within the country, as this is the whole point of SAP: to allow for comparison of properties on a national basis, irrespective of location. Other assessment methods are available that overcome this crudeness, but SAP is the minimum legal requirement.
To explain further: The SAP energy rating scale of 1 to 100+ relates to fuel running costs for the dwelling (not carbon emissions), with the higher the number, the lower the costs. The scale is set so that 100 represents zero energy cost, so a number over 100 would indicate that energy is being exported (from a solar PV array, for example). Remember, however, that this only relates to the energy costs included under the SAP requirements and does not include cooking and appliances, so a dwelling with a score of 100 may still have fuel bills to pay! The SAP rating is adjusted for floor area so that it is effectively independent of the size of the dwelling for any particular built form.
How does it work?
SAP calculations for new build properties can be derived from drawings and specifications, rendering a site visit unnecessary.
Key issues to be considered include:
- Insulation – location and type of insulation being used, width/depth
- Heating – primary and secondary systems specified and fuel used, efficiency, emitters and controls
- Design and build factors – use of accredited construction details and attention to thermal bridging
- Legal requirements – minimum specification of dedicated low energy light fittings, air pressure test limits, minimum thermal element U-values and heating system specifications, building not to over-heat in summer
All of the above key issues, along with additional information, are then entered into a computer programme and an overall Target Emission Rate (TER) for the building is calculated. This is the maximum threshold for carbon emissions relating to SAP relevant annual energy use allowed for the proposed design. A second figure, the Dwelling Emission Rate is also calculated which is the predicted performance of the proposed design. To pass Part L1A of the Building Regulations, this figure needs to be lower than the TER.
SAP/Part L1A Calculations – The Blewburton Partnership approach
The Blewburton Partnership is licensed with NHER to produce SAP reports, Building Control checklists & reports and EPCs for new build dwellings. Prices for individual dwellings start from £80 + vat, depending on complexity.
We recognise that at the early stage of design, not all the information required to assess a dwelling will be available. Nevertheless, as long as the actual dimensions of the building are known, SAP software can be used as a design tool to model a variety of parameters to ascertain the best solution for a particular development. This is particularly relevant when a Code for Sustainable Homes assessment is also required and is strongly recommended.
In all our work, we will offer feedback on potential improvements or concerns we identify. When a design does not comply with Part L1A we seek solutions and make recommendations, such as improvements to U-values through extra insulation or use of alternative products; alterations to boiler specification and heating system control; or the incorporation of renewable/sustainable energy products.