SAP for Self Build - SAP Energy Ratings

Summary: Explanation of the Standard Assessment Procedure for working out Standard Energy Ratings used in Part L of the Building Regulations.

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Energy Ratings for compliance with Part L of the Building Regulations. Standard Assesment procedure for energy ratings.

The text below is a brief description of what is involved with the standard assesment procedure for energy ratings, or SAP.

No matter what domestic building project you are working on, it is almost certain to come under Part L1A (new dwellings) or Part L1B (existing dwellings) of the new building regulations. This is about conservation of heat and power, and reducing the Carbon Emissions from new and existing dwellings.

New Houses

If you are building a new house you will be required to provide a “design stage” energy rating on the house known as SAP 2005 to building control. Your architect should be able to produce the SAP – they will, most likely, use an approved computer program. They will then design the house to accommodate the output SAP requirements, thus producing the design stage SAP and plans to direct the builder.

Once you have built your house you will then need to provide an “as built” energy rating SAP 2005, which includes any changes to the original design plus the results of an Air Pressure test - if that has been required. Once this stage is completed, and passed, you will need to get an Energy Performance Certificate (EPC), and building control submission documents – again from your architect as long as they have become an Accredited Energy Assessor (through a Government approved accreditation scheme). From 6 April 2008 Building Control will not give you your Completion Certificate without the EPC.

From the above description you can see how important the SAP and EPC have become and, thankfully, how your architect should be able to produce the SAP, design the house accordingly, and then produce the EPC.

The SAP calculation uses a large number of inputs for the calculation, taking into account virtually every element of the building, including:

  • the materials used for the construction – each material e.g. bricks, timber, roofing material, has its own insulating property
  • the thermal insulation materials proposed
  • the ventilation characteristics, including any chimneys, extractor fans and the requirement for window ventilation
  • the efficiency of the space and water heating systems and how they are controlled
  • solar gain characteristics of the house and its location
  • the fuels used for space and water heating and lighting
  • any proposed renewable energy technologies.

One common requirement of the SAP calculation is for an Air Pressure Test – to measure the amount of uncontrolled air leakage – which is undesirable as it will tend to leak air which has consumed energy in winter months when it has been heated . The SAP calculation will assume a certain amount of air leakage. For certain SAP results an Air Pressure Test will be required when the house has been completed. It is prudent, when building the house, to assume that a test will be required so that all necessary methods are used to reduce air leakage – your builder should be acquainted with these.

Existing Houses

The SAP 2005 ( Standard Assesment Procedure) software looks at the whole house and uses information on thermal structure for walls, floors, roofs, windows and doors. It looks at heating type and fuel type, secondary heating type, chimneys, ventilation and solar gain plus summer over heating. All these factors are taken into account to produce a carbon emission figure for your house.


Energy ratings may be required if you build an extension which has too much glazing. The rule here is that the area of glazing should not exceed 25% of the floor area of the extension. If it does you then need a whole house energy rating similar to the above approach but slightly more complicated in that a “notional extension” plus the house is used to calculate the carbon emissions and then the carbon emissions from and the “actual extension” and whole house. This is fully documented in L1B.


If you decide to convert a house into two flats you will almost certainly be asked to provide an energy rating for the change of use. This could involve improvements to the existing thermal elements of the property in order to comply with Part L1B.


Removing and replacing rendering from an existing wall could trigger “consequential” improvements to the thermal properties of the wall.

Un-separated Conservatories

If you do not maintain thermal separation between your house and your new conservatory, by means of say an existing patio door. Then you will be asked by building control to provide a whole house energy rating to prove that you have not worsened the carbon emissions from the property pre and post the conservatory.
Very difficult, considering the level of glazing in a conservatory.

Take a look at our video section on Green Living to watch a film on how to get the best energy efficiency from your fridge.

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