What is the “As Designed” stage of a SAP Calculation?

The accredited energy assessor uses the plans, drawings and specifications you provide to prepare summary information for the dwelling.  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.

If your architect has not already done so, your assessor will then calculate the performance of the thermal elements (walls, roof, floor etc).  These are expressed as U-valuesU-values express the rate at which heat passes through the fabric of the building.  The higher the U-value, the greater the rate of heat loss and therefore the worse the energy performance of the element.

Your assessor will then input all this data into the approved software and 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;
  • Internal 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.

Rarely, the initial draft and specification will pass the assessment by meeting all the requirements.  Normally the assessor will need to work with you and your design team to model different variations of the design until a version is developed that meets all the requirements.  The assessor can advise the designer of the shortfalls and suggest possible solutions as required.

This is why it is so important to involve an accredited energy assessor as early as possible in the design process.  Having to make changes after construction has taken place can be both expensive and time consuming.  All to often we are only approached at the end of construction which causes unnecessary stress and expense.  As more local authorities are enforcing their own requirements, it is becoming more and more common for some of this work to be completed prior to an application for Planning Permission being submitted.

By the end of this stage, your energy assessor can provide you with the reports that you need to submit to Building Control for them to advise you during the construction phase.  This will include a Predicted Energy Assessment which provides a rating of energy performance based upon the specified design.

WARNING:  This is often where things start to go wrong!  Our experienced assessors know that in the real world changes during the construction phase are almost inevitable.  Changes occur due to a wide range of reasons which may include discoveries on site, supply issues, budgeting measures or even special offers from suppliers.  However, you must remember changes from the agreed design are likely to result in changes to the performance of the building.  Please, keep in contact with your assessor during the building works and discuss changes with them before you commit to them.  They can check to make sure your final building will still meet the requirements and won’t require expensive remedial works.