Many people come to us wanting to understand what a SAP calculation is and whether their project needs one. This is a brief explainer for anyone in this position.
What is a SAP Calculation?
SAP stands for ‘Standard Assessment Procedure’. It is the only government-approved method for calculating the energy performance of dwellings. They have been a requirement for all newly built dwellings in the UK since 1995 under Part L of the Building Regulations and are necessary in order to produce a Predicted Energy Assessment and an Energy Performance Certificate. Building Regulations require that a SAP calculation and a Predicted EPC be submitted for new dwellings prior to the commencement of work.
SAP calculations are not only used to demonstrate compliance with Part L and to produce an EPC, they are also used to determine a SAP score/rating. The SAP indicates a score between 1 and 100+, which estimates the annual energy-related running costs of a dwelling. The higher the rating, the lower the running costs, with 100 representing zero energy cost. Dwellings in excess of 100 are net exporters of energy. Therefore, the higher the SAP score, the lower the fuel costs and the lower the associated emissions of Carbon Dioxide (CO2).
These calculations are only necessary for residential properties. In England, the SAP calculations measure two elements: the Dwelling Emission Rate (DER) and the Dwelling Fabric Energy Efficiency (DFEE). These calculations are used to determine a Target Emission Rate (TER) and a Target Fabric Energy Efficiency (TFEE). The DER and DFEE must be lower than the TER and TFEE respectively.
SAP calculations allow comparison to be made of the energy running costs of dwellings anywhere in the UK. This is achieved as 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 people use their homes.
Do I Need a SAP Calculation?
A SAP calculation is required under Part L (England and Wales) of the building regulations. These documents are concerned with the conservation of fuel and power. They were first introduced in 1995 but have since been amended several times due to changes in the availability and effectiveness of new and emerging technologies. Homes builders need to gain a ‘pass’ on their SAP calculations in order to meet current Building Regulations. Without a pass, building control will not sign off the development, and the property cannot be let or marketed for sale. To gain a pass a number of compliance targets must be met in relation to:
- How well the fabric of the dwelling contains heat
- Solar gain
- Quality of construction
- Commissioning of systems
- Predicted CO2 emissions from the dwelling
SAP calculations are necessary in order to produce a new or up-to-date EPC. An EPC Is required by law to rent or sell a residential property. EPC rates a property between A (best performance) and G (worst performance) across two measures: energy efficiency rating and environmental impact rating. Since April 1st, 2018 it has been against the law to rent a property with an F or G rating in either category.
How are SAP Calculations Completed?
SAPs should be completed before the building work starts. In order for a SAP calculation to be undertaken, the client must provide as much information as possible. This includes but is not limited to:
- Floor plans
- Site plans
- Insulation type/thickness
- Specification of heating systems
- Hot water generation
- Percentage of low-energy lighting
- Specification of ventilation system
- Renewable technologies
- Accredited construction details
- U-value of openings
U-values represent the rate at which heat passes through openings/building fabric. The higher the U-value the greater the rate of heat loss.
After this information has been collected, the SAP usually involves 4 stages:
Design Draft: Stage 1
- From the plans and drawings provided by the designer, the SAP assessor will prepare a summary of the numerical information such as the total floor area; the floor area of the living room; the areas of the heat loss floors and heat loss roofs; dimensions of external windows and door and story heights. The assessor will then use the specification provided by the client to calculate the performance of the thermal elements, expressed as U-values, which are then input in the SAP calculation.
- The software then determines whether the proposed dwelling will comply with the requirements of Part L in regard 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.
Design Final: Stage 2
- The client, designer, and assessor agree the finalised version of the design which may involve amendments to the initial design in order to achieve SAP compliance. Data from the finalised design is input into the software.
- The assessor will then produce a report that the client or designer will need to submit to Building Control, including a Predicted Energy Assessment which provides a rating of energy performance based on the agreed design.
Built Draft: Stage 3
- For the majority of newly built dwellings, an Air Pressure Test (APT) will normally be required. The client or designer provides the result of the APT to the assessor and also advises of any variations from the specification. The assessor will edit the SAP Calculation to reflect the result of the APT and any variations to the specification. The software is used to check that the completed dwelling still meets the requirements of Part L. If it does not the assessor then 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.
Built Final: Stage 4
- The assessor finalises the SAP calculation and eventually creates the EPC. This then provides a rating of energy performance based on the dwelling as built. The EPC must, by law, be displayed in a new dwelling put up for sale.
- Additionally, there are other documents that are required by Building Control such as SAP worksheet report and the SAP data input. The assessor provides the clients with the reference of the EPC so that the client is able to obtain a copy from the government’s central EPC Registry.
What happens if my building fails a SAP?
It is crucial that your building passes its SAP, because if it fails it is against the law to rent or sell a property without an EPC. This is why it is important that the SAP assessor is involved from the early stages of the design process. They can definitely assist the designer and architect in shaping the energy profile of the dwelling. This then minimises its energy use and carbon emissions and helps to prevent any costly redesign. This becomes more difficult and expensive later in the project issues are addressed. This is because the scope of changes available become more limited.
How do I make sure I pass my SAP?
- Minimum U-values should be exceeded
These U values should be exceeded not just followed, where possible. If the fabric of the dwelling is well insulated, expensive renewable technologies will not be necessary to get a pass. Design as much insulation into the walls, floors, and roofs as possible.
- Thermal Bridging
Heat loss through the junctions with external walls is specifically known as thermal bridging. In order to avoid the assessor using default figures, follow a scheme such as Accredited Construction Details.
- Windows and Doors
Pay attention to the U-values on the opening you are specifying. Get them as low as possible, ideally 1.4 Wm-2K or less.
- Air Tightness
All new builds require APT on completion and the resulting figure goes into the SAP calculation. Make sure that the envelope is sealed and get a pre-test check carried out. It is important to remember that the more airtight a dwelling is the better the ventilation system needs to be. This is to prevent the build-up of condensation.
Our sustainability consultants have extensive experience in meeting regulatory requirements. They work hard to go beyond mere compliance with building regulations. Their approach is to significantly reduce the amount of assumed data in each calculation to the bare minimum. This means that our SAP calculations are as accurate as possible.
So if you need support with your own SAP calculation, get in touch with our friendly team.
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