SAP Information

With effect from the beginning of October 2010, a new SAP methodology has been implemented as the standard measurement all UK new builds.

The 2010 methodology works alongside changes made to the Part L Building Regulations, to require all new UK builds to demonstrate an enhanced energy performance. These changes make significant new demands on SAP 2009 applications.

Hilsdon Holmes is committed to providing comprehensive information regarding these changes on our website. We are also monitoring the 2013 Part L and SAP changes, and we will be providing regular updates on the most recent requirements.

Hilsdon Holmes’ Summary Report of 2010 SAP Changes

29th Sep 2010 – SAP 2009 Summary (Source: Dyfrig Hughes – NHER)

Effective from 1st October 2010, SAP 2009 comes into effect alongside the revised 2010 Part L Building Regulations. Hilsdon Holmes has been monitoring the changes since their inception so we have a pretty comprehensive understanding of what they mean for our clients.

The SAP 2009 changes are important because they have an impact on the ways in which new builds are designed and constructed. The Part L1b revisions have implications for extant buildings and extensions.

Two Key Aims of SAP 2009

  • An improvement in the accuracy arrived at by the SAP methodology
  • Enhanced flexibility, allowing combinations of technologies (new and existent) to be utilised within a building.

Impact of SAP 2009

As a result of changes to the SAP methodology clients can expect to see:

  • Higher predictions for energy consumption (heating), which will be offset, in part, by a decrease in hot water usage.
  • For builds integrating air conditioning systems, the changes now require consideration of the cooling load which will mean a higher energy use prediction.
  • Co2 emissions per unit of energy will be calculated differently. Co2 emissions per unit of electricity will increase by 23% as a result of SAP 2009.
  • SAP 2009 will affect the DER (Dwelling Emission Rate) and the TER (Target Emission Rate). The DER and TER form the basis for calculations concerning Co2 emissions per square metre of the floor area for energy consumption.  The outcome will be that housing developers will find it more difficult to successfully design a Zero Carbon home.

What will the impact of SAP 2009 be upon the design and construction of new builds?

1. Party Walls

SAP 2005 - heat loss through party walls should be registered as zero.

SAP 2009 - the U-value of a cavity party wall is set at  0.0 and 0.5 W/m2/°C, depending upon the specification.

Research emerging from Leeds Metropolitan University has shown that cavity walls allow for air movement which – in turn – produces the potential for heat loss. The internal location of party walls heightens the potential for this loss. Findings reported with this research showed that U-values for cavity party walls were estimated at between 0.50 and 0.63, whilst external wall U-values were estimated at 0.23. The floor’s estimated U-value was shown to be 0.17. The outcome of this research, as it impacts on SAP 2009, is that designs for new builds must now demonstrate the elimination of this air-movement; this may be achieved through filling and sealing the cavity in the party wall.

The U-values assumed by SAP 2009 are:

  • 0.50 for an unfilled, unsealed cavity;
  • 0.20 for a sealed unfilled cavity
  • 0.0 for a fully filled and sealed cavity.

If you would like to read the Leeds Metropolitan Research Paper, which details ways of addressing heat loss in cavity party walls:

2. Thermal Bridges

SAP 2005 – it is acceptable practice to assess the impact of non-repeating thermal bridges very easily by adopting Accredited Construction details and assigning an effective U-value (the ‘y’ value) of 0.08 W/m2/°C.

SAP 2009 - The only ‘y value’ option available in SAP 2009 is the ‘worse case’ value of 0.15.

There was no evidence that the Accredited Construction Details Approach was delivering on the thermal performance promised in the SAP 2005 calculations. The Calculation will now be based upon measurement of losses through each specific thermal bridge, which are then added up and totalled.

The loss of heat at thermal junctions will become ever more important as U-Values are further reduced as a means of achieving reductions in Co2 emissions. SAP 2009 requires assessors to make a detailed assessment of all junctions (walls, floors, windows, doors) in order to accurately assess the heat being lost through these thermal bridges.

These changes may have the result of raising the calculated thermal bridging heat loss, when compared with the SAP 2005 calculation. Significantly, SAP 2005 allowed party wall junctions to be ignored whereas all thermal bridges now need to be calculated in the total.

3. Cooling and Air Conditioning

SAP 2005 – requires a risk assessment related to the potential for summer overheating resulting in increased air-conditioning usage and a rise in Co2 emissions

SAP 2009 – allows for assessments of cooling requirements and related energy and Co2 emissions. This will result in dwellings with fixed air conditioning experiencing a higher DER.

Air conditioning systems run on electricity and can, therefore, produce significant Co2 emissions.

  • A 3 kW system running continuously for four hours per day from June to August would produce around 650 kg of CO2.

On this basis the DER in a dwelling with a floor area of 150 m2 would be over 4 kg CO2/m2 (as compared to a typical DER in a 2006 Regulations dwelling of around 22).

SAP 2009 takes into account the following:

  • A-to-G rating of the unit
  • Thermal mass of the build
  • Regional average external temperatures in the region that the dwelling is located.

SAP 2009 takes 24°C as the temperature to be achieved by cooling systems. This creates an impact in that the increase in the DER due to the air conditioning is likely to be much less than 4 kg CO2/m2.

Significantly SAP 2009 recognises that there will be regional variations in the cooling load; it will not be the same in the Highlands of Scotland as it is Cornwall or Kent.

4. Thermal Mass

SAP 2005 – takes thermal mass into account

SAP 2009 – uses thermal mass in the calculation of the heating and cooling load.

Thermal mass allows assessors to measure whether a building should be designated as ‘lightweight’ or ‘heavyweight.  ‘Heavyweight’ buildings have demonstrated the potential for energy efficiency in that the build materials are able to absorb solar gains throughout daylight hours and continue radiating the stored heat throughout the hours of darkness.

The estimated difference between ‘lightweight’ and ‘heavyweight’ buildings using the SAP 2009 calculation is a 1% difference between the two.

5. Hot Water

SAP 2009 - The estimated hot water consumption of a dwelling drops; there is a particular impact felt in larger builds.

If you are designing a build which seeks to achieve the water-use target of 125 litres per day – for all water use – the hot water usage estimate drops by 5%

6. Multiple Heating or Ventilation Systems

SAP 2005 – allows one central heating system, with the back-up of one room heater.

SAP 2009 – allows for two central heating systems or boilers running on different fuels.

In SAP 2009 the two separate systems can be used; the calculation will be based on the floor area served by those systems.

The changes represented by SP 2009 allow for the provision of Community Heating Schemes. It is

7. Heat Pumps

SAP 2005 – the COP (Coefficient of Performance) of a heat pump was subject to a fixed SAP Calculation

SAP 2009 – manufacturers can add their heat pumps to a database which contains the COP.

8. Innovative Technologies

SAP 2005 – introduced Appendix Q, enabling innovative technologies to be appended as they are introduced.

SAP 2009 – maintains Appendix Q and allows for the addition of multiple systems.

9. CO2 Emission Factors

SAP 2009 - revises  Co2 emissions per kWh of fuel used. Examples: the factor for electricity increases from 0.422 to 0.517, i.e. a 23% increase. By contrast, mains gas goes up from 0.194 to 0.198¯a 2% increase.

Revisions require substantial drop in the emissions associated with community heating schemes running on waste combustion (down 30%), biomass (down 48%) and biogas (down 28%).

In individual heating systems, wood chip emissions go down (64%); wood pellets in bags emissions  go up (12%). The reasons for these changes are - in part – due to the fact that more factors are now included in the calculation, such as transport.

These changes make the achievement of a zero, or low carbon, home more difficult if individual heating systems are utilized. If, however, community heating systems are in use, the low carbon ambition becomes more realisable.

10. Lights, Appliances and Cooking

SAP 2009 – there are two ways of assessing the contribution of lights, appliances and cooking, as well as taking into account the people-based heat gains, solar gains and pipework heat gain.

The DER will assume a level of gains that is around 33% lower than that assumed in the SAP rating. The aim of this change is require developers to reduce the energy demand of the build to levels that assume the presence and widespread use of low-energy appliances and lighting.

The SAP incidental gains are used for the cooling and summer overheating assessments.


SAP 2009 will have a significant impact in the following ways:

  • Cavity walls need to be sealed and insulated
  • Detailed attention should be paid to thermal bridges throughout the property

Energy Performance Certificates

Energy Performance Certificates (SAP EPC) are necessary for all new build projects using SAP 2009 Methodology, and progressed by an OCDEA (On Construction DEA).

Note: SAP 2009 requires Design Stage SAP Calculations to be submitted before work starts on site.

Quality Assured SAP 2009 Energy Ratings

Hilsdon Holmes provides a high quality SAP 2009 Assessments. We are accredited by NHER and Stroma licensing bodies.

Our SAP 2009 software is approved by BRE on behalf of the Department for Environment, Food and Rural Affairs (DEFRA), The Department of Communities and Local Government (DCLG), the Scottish Executive, The National Assembly for Wales and the Department of Finance and Personnel.

Want to discuss your SAP project? Just give us a call on 01579 382202 or send us your enquiry - we’ll get straight back to you.