When a client or their designer submits drawings, plans and specifications of the development to a SAP assessor, a desktop exercise is carried out-using specialist software. We recommend that the SAP calculation is undertaken early in the design process. This will prevent any re-designs, which may be costly.

Usually, SAP calculations involve three main stages. This blog aims to explore each stage in-depth for anyone looking to understand the SAP calculation process further.

Read on to find out more.

SAP calculations ebook | Sustain quality

As Designed Stage

During this stage, the accredited assessor prepares summary information based on the suitably scaled and fully dimensioned plans and drawings provided by the client/agent. This includes:

  • The total floor area of the dwelling,
  • The floor area of the warmer living area,
  • The areas of the heat loss floors, walls and roofs
  • Dimensions of external windows and doors; storey heights, etc.

Using the specification provided, the assessor calculates the performance of the thermal elements. These elements are expressed as ‘U’ values, which means the rate at which heat passes through the fabric of the building.

This data is then input into the SAP calculation software. Data entered is related 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 SAP 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 software has the ability to model different variations of the design if the initial specification design doesn’t show compliance. The SAP assessor can then advise the designer of the shortfalls and recommend appropriate solutions.

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 and is required to market the property).

2. Build stage

Considering that any changes on site can have a huge impact on the SAP, we suggest that these are checked prior to any changes.

At Built Stage, the assessor will edit the SAP calculation to reflect the results of the air pressure test and any variators to the specification. The software is then used to check that the completed dwelling still meets the requirements of the Building Regulations. If it doesn’t meet those requirements, we would recommend remedial action.

For new builds, we would check to ensure that the dwelling is registered on the Government’s central database of national property address. If this is not the case, we would arrange for the address record to be created.

3. As Built Stage

Upon project completion, we finalise the SAP calculation and create an Energy Performance Certificate.

In general, SAP calculations are based on a desktop exercise and not a site survey, highlighting the importance of correct information being submitted at the earliest possible stage.

Here is a minimum suggested list of the information sources and data items required:

  • Site address and postcode
  • Site plan to include orientation of the dwelling(s)
  • Plans of each storey
  • Elevations drawings for each elevation to a recognised scale
  • Sectional drawings of the dwelling
  • A written specification


If you would like to find out more about our SAP calculation services or would like to speak to one of our team members about energy advice for your property, get in touch on 01372 438 039 or fill out the form below and we’d be more than happy to help.

SAP calculations ebook | Sustain quality

Want to find out more? Fill in the form below and an expert will be in touch soon!

About Us

We are a friendly team of Engineers delivering Sustainability and Building Compliance Solutions for developments in the Commercial and Residential sectors, which include Energy Statements, Noise Impact and Vibration Assessments, BREEAM Assessments, and Air Quality Assessments in the Environmental, Social and Governance sectors.

Contact us at:

Sustain Quality Ltd

PO Box 393


KT11 3EL


01372 438039