A SAP rating is the calculation that is required in order to produce a Predicted Energy Assessment and an On Construction Energy Performance Certificate. Building Regulations require that a SAP calculation and a Predicted EPC is submitted for new dwellings priorto the commencement of work.
A SAP calculation indicates a score from 1 to 100+ for the annual energy cost based on:
The higher the score the lower the running costs, with 100 representing zero energy cost. Dwellings with a rating in excess of 100 are net exporters of energy. SAP calculations allow comparison to be made of the energy running costs of dwellings anywhere in the UK. This is achieved because the calculations are predominantly location independent and are based upon a notional standard occupancy that overcomes variations associated with physical location and the differing ways in which people utilise their homes.
From the plans and drawings provided by the designer, the assessor prepares summary numerical information which includes the total floor area of the dwelling; the floor area of the lounge or living room; the areas of the heat loss floors, heat loss walls and heat loss roofs; dimensions of external windows and doors; storey heights and so on.
From the specification provided the assessor calculates the performance of the thermal elements. These are expressed as 'U' values (the rate at which heat passes through the fabric of the building), the higher the 'U' value the greater the rate of heat loss. The assessor then inputs this data into the SAP calculation. Data is entered relating to:
The software determines whether the proposed dwelling will comply with the requirements of the Building Regulations with regards to the conservation of fuel and power. The assessor is able to use the software to model different variations of the design if the initial specification doesn't show compliance. The assessor should then advise the designer of the shortfalls and recommend solutions as required.
The client, designer and the assessor agree the finalised version of the design, this may involve amendments to the initial design in order to achieve SAP compliance. Data from the finalised design is input into the computer program. From this the assessor produces reports that the client or designer need to submit to Building Control, this will include a Predicted Energy Assessment (this provides a rating of energy performance based upon the specified design).
For the majority of new dwellings an air pressure test will normally be required (for small sites of 2 dwellings or less an air leakage value of 15 m 3 /(h.m 2 ) may be used in the calculation and no test is required). The client or designer provides the results of the air pressure test (if required) to the assessor and also advise of any variations from the specification.
The assessor will edit the SAP calculation to reflect the results of the air pressure test and any variations to the specification. The software is used to check that the completed dwelling still meets the requirements of the Building Regulations with regards to the conservation of fuel and power. If it does not the assessor recommends remedial action. For new build dwellings the assessor checks to ensure that the dwelling is registered on the Government's central database register of national property addresses. If it is not the assessor arranges for the address record to be created.
The assessor finalises the SAP calculation and creates the Energy Performance Certificate (this provides a rating of energy performance based upon the dwelling as built). The EPC must, by law, be displayed in a new dwelling put up for sale on the open market. In addition there are other documents that are required by Building Control such as the SAP worksheet report and the SAP data input report.
The assessor provides the client with the reference of the EPC so that the client is able to obtain a copy from the Government's central registry website at: www.epcregister.com/.
Building Regulations require that an Energy Performance Certificate is provided prior to a completion certificate being issued.
Since SAP calculations are based upon a desktop exercise, and not a site survey, it is critical, that the correct information is submitted, the following is a suggested list of the information sources and data items required.
A written specification which must include:
SAP is the shortened form of Standard Assessment Procedure and is used to assess a dwelling's energy performance.
Approved Document Part L and Section 6 of the Scottish Building Standards require an SAP calculation to be carried out to demonstrate compliance with energy performance requirements.
SAP calculations are also required to demonstrate energy performance in the Sustainability benchmarks such as the Code for Sustainable Homes and in some planning conditions.
The earlier the better. DER/TER calculations need to be submitted to building control before work starts on site, however getting them done further in advance will allow for the energy efficiency of the dwelling to be considered whilst it is being designed ensuring a cost effective solution to compliance is achieved.
SAP is generally a term that describes the design stage DER/TER (Dwelling Emission Rate/Target Emission Rate) Calculation, an Energy Performance Certificate is calculated from an As-Built SAP and represents the dwelling as constructed included an air test result.
SAP calculations and EPCs require drawings of the dwelling (floor plans, elevations, sections and site plan) as well as a build specification. An EPC will also need an air test result either for the specific or similar dwelling.
SAP calculations submitted for building control should demonstrate the performance of all the dwellings on the site. Due to the number of items that will cause the calculation to vary, a large proportion of the dwellings will require an SAP assessment and builders often have an SAP for every dwelling. This also helps with a plot specific Predicted Energy Assessment (PEA) and also Code for Sustainable Homes assessments.
Thermal bridging occurs where insulation cannot be continued. Non linear repeating thermal bridges are caused by wall ties and timber battens etc, and is taken into account in the u-value calculations. Linear thermal bridges occur where two different elements occur such as corners and where the ground floor meets the external wall. For more information on thermal bridging see NHBC Technical Extra 3.