SAP Calculations (Building Regulation Compliance)

SAP calculations are used to predict the energy efficiency of new domestic buildings.  If you are constructing a new house or flat in the UK you will need to have SAP calculations completed by an accredited energy assessor in order to obtain an EPC on completion of your property.  You may also require SAP calculations for an extension depending upon its size and nature.  If you are unsure if you require calculations for an extension then please contact us or your building control officer to discuss this.

For new dwellings, a SAP calculation and a Predicted EPC should be submitted to building control before construction work is started.  However, we often find clients only discover that they need SAP calculations at the end of their project, once the building has been constructed.  This is not the way the system is intended to work. Leaving it this late can also make compliance much more difficult and expensive.  If your building requires improvements to meet the minimum energy standards required, you may find you have to redo parts of the construction to retrofit improvements.  Involving us early in the project (at the design phase) can not only prevent this but also save you money.  Our experienced assessors can help advise you, helping you comply in the most efficient manner for your specific building. 

A SAP calculation for a new dwelling is a desktop exercise.  The client or their designer submits drawings, plans and specifications of the development to the accredited assessor for use in the calculations. It is recommended that the SAP calculation is undertaken early in the design process, this will help to prevent any costly redesign of the dwelling.

A full SAP calculation will usually involve 4 key stages:

  1. As Designed (Draft)
  2. As Designed (Final)
  3. As Built (Draft)
  4. As Built (Final)

Building Regulations are an area of legislation that has now been devolved in the United Kingdom to each of the different administrations.  At the moment the rules in England and Wales are essentially the same, however different rules and systems apply in Scotland and Northern Ireland.  Additionally, some areas have additional requirements as part of the planning process.  Here at Rowleys Commercial Energy Assessment Limited, our assessors are used to working with your building control officer to help you through this complex process wherever your building is located.

The cost of SAP calculations can vary significantly depending of the size and complexity of your project.  Please contact us for a quotation supplying as much information about your project as you can.  We are always happy to discuss your specific requirements with you.

FAQ: SAP Calculations

Once construction is complete and the final details have been confirmed, the assessor finalises the SAP calculation and creates the Energy Performance Certificate.  The EPC provides a rating of energy performance based upon the dwelling as it has been 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 will provide all of these documents to the client to pass on to their Building Control officer to enable the completion to be signed off.  The exact process here depends upon the location of your building as the system is different is some parts of the UK.

During construction it may be necessary to make some amendments to the design.  Keeping your assessor informed during this process and seeking their advice prior to confirming any changes will help to ensure that your finished building will comply with the regulations.

Once construction is complete an air pressure test (sometimes called an air tightness test or air leakage test) may be required.  This test confirms the air tightness of the finished building to ensure it is energy efficient.  Once the test is complete you will need to provide details to your energy assessor.  If an air pressure test is not required you may still wish to obtain one.  If the result of a test is not available then the assessor will use a default value in the SAP calculations which is worse than most well constructed buildings will obtain.  Having a test conducted voluntarily is likely to improve your final rating and help demonstrate that you have complied with the regulations.

During this stage the assessor will edit the SAP calculation to reflect the results of the air pressure test and any variations to the specification.  The approved 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 for any reason the building does not meet the required standards, the assessor can advise remedial action to get your project back on track.

The assessor will also check to ensure that any new building is registered on the Government’s central database register of national property addresses.  If it is not, the assessor will arrange for the address record to be created.

Once the As Designed (Draft) stage has been completed, the client, building 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.

The data in the approved software is then updated to reflect this final design.  The software is then used to produce the 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).

The accredited energy assessor uses the plans and drawings provided to prepare summary information for the building.  This includes calculating 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; the dimensions of external windows and doors; and storey heights etc.

The assessor then calculates the performance of the thermal elements from the specifications provided. 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 all this data into the approved software to produce the SAP calculation.  Data is entered relating to:

  • Type of dwelling;
  • Floors;
  • Walls;
  • Roofs;
  • Openings (windows, doors, roof lights);
  • Ventilation;
  • Main and secondary space heating;
  • Hot water generation;
  • Renewable technologies, including photovoltaic panels and solar water heating;
  • Energy efficient lighting.

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 can then advise the designer of the shortfalls and recommend solutions as required.

SAP calculations are produced using a computer model.  They do not require the assessor to visit the site of the building.  As a result it is important that accurate and reliable information is submitted to the assessor.

The exact information required will vary from project to project and your assessor will discuss this with you.  The following is a list of the information typically required:

  • The full building address.
  • The correct postcode as confirmed by Royal Mail.
  • A site plan including the orientation of the dwelling(s).
  • Scaled plans of each storey of the building (normally at 1:100).
  • Elevations drawings for each elevation.
  • Sectional drawings of the dwelling.
  • Details of the principal heating and hot water system. This needs to include the make and model of boiler, details of heating emitters (e.g. radiators), hot water cylinder size (if applicable) and the system controls.
  • Details of any secondary heating system present.
  • Details of ventilation systems or extractor fans.
  • Details of the internal and external lighting.
  • Details of the construction of all the different floors to the property.  This needs to include the type and thicknesses of insulation and any other building products used.
  • Details of the construction of all the different external walls to the property.  This needs to include the type and thicknesses of insulation and other building products used.
  • Details of the construction of all the different roofs to the property.  This needs to include the type and thicknesses of insulation and other building products used.
  • Details of all the doors and windows.  This needs to include the sizes, type of frame, type of glazing, thickness of glazing and any low emissivity applications.
  • Details of any renewable technologies installed in the building.  These could include ground source heat pumps, air source heat pumps, solar water heating, photovoltaics (PV), wind turbines and/or hydrokinetic technologies.

If you are in the process of designing your building, the assessor will be able to help you decide the minimum standards for each system to ensure that your finished building meets the required energy performance standards.

A SAP calculation works out the rating that is required in order to produce a Predicted Energy Assessment and an On-Construction Energy Performance Certificate for a new domestic building.

A SAP calculation indicates a score for the predicted annual energy cost for the new building based on:

  • The elements of structure;
  • The internal lighting;
  • The heating;
  • The hot water system;
  • Any renewable technologies installed in the home.

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.

The model used to produce a SAP calculation is largely location independent.  It is also based on a notional occupancy to overcome the different ways in which people use their homes.  As a result, SAP calculations allow the energy running costs of dwellings anywhere in the UK to be compared.

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