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SAP Calculations

What are SAP calculations?

The Standard Assessment Procedure (SAP) is used to measure the energy efficiency of a residential property. SAP calculations are a requirement of Part L of the Building Regulations requirement for all new houses, conversions and some extensions. They must be carried out by an accredited organisation such as Surrey Energy Management.

SAP measures the annual energy cost for space heating, water heating, ventilation and lighting; and also quantifies the total CO2 emissions from the property each year. This information is also used to produce an Energy Performance Certificate (EPC).

SAP sets a target for all new dwellings based on a notional dwelling of the same floor area built to pre-1st Oct 2010 Building Regulations, plus a 25% improvement factor (TER). The new dwelling (DER) must produce lower CO2 emissions than the TER to achieve a Building Regulations pass.

When are SAP calculations required?

To meet Building Regulations requirements, SAP calculations must be carried out for:  

All new dwellings and domestic conversions (conversions are done in a slightly different way to new buildings, but the principles are the same).
Domestic extensions with lots of glass (more than the equivalent of 25% of the floor area)
What is involved?

Design Stage calculation: Initial calculations are done at design stage to ensure that the property will meet the minimum SAP requirements.

‘As Built’ calculation: When the property is finished, an air leakage test is carried out and the Design Stage SAP calculations are updated to provide a final SAP rating and EPC.
To produce SAP calculations we require a full set of scale plans (inc. sections, elevations and a site plan including orientation).
Energy Performance Certificates (EPC)

All new houses and conversions are required by Building Regulations to have an On Construction EPC. This can only be produced by ‘On- Construction’ an accredited SAP assessor such as Surrey Energy Management.

What influences SAP Ratings?:

  • The shape & orientation of the dwelling
  • Heating systems, controls, boiler efficiency and type of fuel used
  • Thermal efficiency of walls, floors, roof, windows and doors
  • Proportion of low energy light fittings
  • Thermal bridging
  • Renewables - solar panels, heat pumps, bio fuel boilers, certain wind turbines etc. can improve SAP ratings
  • Air tightness testing results



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