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SAP Calculation Changes for 2019

SAP Calculation Changes for 2019

  • Posted on 1st February 2019
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SAP calculations are used to determine the energy performance of dwellings in the UK and form part of the Building Regulation compliance. The SAP document is usually updated every four years but the current one was issued in 2012 and therefore the latest SAP calc, referred to as SAP10 currently, is long overdue. The SAP10 methodology has been issued but will not come into effect until the Building Regulations Part L are revised in 2019 or 2020. However, the Greater London Authority has announced that the new CO2 emission factors included in SAP10 need to be used in all dwelling designs from 1st January 2019.

What is the main change in SAP10 and how will this affect our building designs?

The biggest change to the SAP calcs is the changes in the carbon emissions factor for electricity. Currently the SAP calc assumes that any electricity used produces 2.4 times more carbon than mains gas.

The new carbon emission factor takes into account the amount of renewable power being generated in the UK which is being fed into the national grid. The current carbon emissions factor and the proposed new emissions factors are shown in Table 1 below.


   Emissions Kg CO2e per KWh

                                          Current SAP (2012)             Draft new SAP10

Mains Gas                                  0.216                                     0.210

Electricity                                    0.519                                     0.233

Table 1 – Proposed change in CO2 emission factors

This change alone will start to see an increase in electricity use in apartments for heating and hot water. However, with the price of electricity still significantly higher than gas, the incorrect choice of heating and hot water plant could lead to higher energy bills for end users.

What are the other changes in SAP10?

• CO2 emission factors, primary energy factors and fuel prices, have been updated
• Default distribution loss factors associated with heat networks have been increased
• The assumed heating pattern has been changed to a consistent daily pattern for all days of the week
• The assessment of summer internal temperatures has been refined
• Additional design flow (heat emitter) temperature options have been provided for heat pumps and condensing boilers, which affect their efficiencies
• Default heat pump efficiencies have been updated
• The calculation of lighting energy has been updated to allow recognition of new lighting types with higher efficacy
• The options for entering heat losses from thermal bridges have been revised
• The calculation of hot water consumption has been adjusted to account for shower flow rate
• Battery storage is now accounted for in calculations for PV panels
• The impact of PV diverters is now taken into account
• The overshading factor used for the PV calculation can be taken from Microgeneration Certification

For more information regarding these changes, please contact Elaine Bissell at