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To comply with the current Building Regulations all new dwellings are required to have a SAP (TER/DER) calculation which should be carried out before construction commences. On completion the SAP is re-calculated using “As-Built” information such as the boiler details, pressure test result and details of any renewable energy appliances (solar) installed. This then provides the information which is included in the EPC (Energy Performance Certificate).


SAP (Standard Assessment Procedure) ratings were first introduced in 1995 and are the Government’s recommended system for the energy rating of new dwellings. Since it’s commencement the system has been upgraded three times to further reduce the carbon footprint of new dwellings:


  1. SAP 2001 was introduced in December 2001 when the system had a scale from 1 to 120 and the rating was solely based on the annual energy costs for space and water heating where 1 was very poor and 120 was excellent. This system is still used to provide calculations for dwellings that have been recently completed but had their Building Regulations approved prior to April 2006. If an EPC is required on one of these dwellings the calculations have to be converted to the SAP 2006 calculation.
  2. SAP 2006 was introduced in April 2006 with a new scale from 1 to 100 where again 1 is very poor and 100 is virtually self sufficient. This calculation introduced the TER/DER values where the TER is the Target Carbon Dioxide Emission Rate, which is calculated by the SAP programme based on a notional dwelling of the same size and configuration but calculated on the 2001 system with a 20% improvement. The DER is the Dwelling Carbon Emission Rate calculated on the proposed design (which should be based on the current Part L of the Building Regulations), and this figure must equal or preferably better the TER figure. The only exception to the above is where dwellings are created by the conversion of an existing building.
  3. SAP 2010 was introduced on 1st October 2010 and the scale is still 1 to 100. The basis is still the same as for SAP 2006 but more emphasis has been placed on using renewable energy, better fabric energy efficiency and thermal mass. The TER is now calculated by the SAP programme based on a notional dwelling of the same size and configuration but calculated on the 2006 system with a 25% improvement. The DER is calculated as before.
  4. The Scottish version is similar but there are some slight variations to the programme and to the values used in the calculation.


In all cases (even for extensions) most Building Controls require the calculations to be submitted with the Building Regulation application. Constructing a dwelling under a Building Notice is extremely risky as a SAP (TER/DER) will still be required before Building Control can provide a completion certificate and if the dwelling fails the calculations remedial works could be extremely expensive.


For new dwellings the standard U-values for the thermal elements (as detailed later) are only a guide because there are so many other factors that affect the TER/DER figures. In most cases these U-values will have to be bettered (sometimes considerably) in order for the dwelling to achieve a TER/DER pass.


The following is a list of items which are now included in the SAP calculations and have the most effect on the TER/DER ratings:


  • Orientation of the dwelling.
  • Area of glazing – solar gain.
  • Ventilation.
  • Thermal Bridging and Air Leakage – Pressure Test.
  • Energy Efficient Lighting.
  • Use of green energy (heat pumps and solar).
  • Heating Controls.
  • Secondary Heating (wood burning stoves), especially where these can be integrated with the main heating system.


The current U-values are as follows:


                                            New Dwellings               Conversions

Walls                                     0.28W/m2K                 0.30W/m2K

Ground Floors                       0.22W/m2K                 0.25W/m2K

Flat Ceilings                           0.16W/m2K                 0.16W/m2K

Sloping Ceilings                     0.18W/m2K                 0.18W/m2K

Flat Roofs                              0.18W/m2K                 0.18W/m2K

Glazing                                  1.60W/m2K                 1.60W/m2K

External Doors                      1.80W/m2K                 1.80W/m2K


The highlighted figures show the elements that have changed in the 2010 regulations.


Typical SAP Values

An existing average dwelling would most probably only achieve a SAP rating of about 45 whereas a new dwelling built to comply with the current Part L of the Building Regulations should achieve a SAP rating of 75-80 (depending on the type of heating fuel used). 







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