Changes to Simplified Building Energy Model


Industry News

Changes to Simplified Building Energy Model

The following changes to iSBEM came into force in England only on 15th June 2022:

Carbon Emission Factors

Carbon emission factor is a coefficient which converts activity data into Greenhouse gas emissions. A significant change to the carbon emission factor for electricity has been implemented within the updated version. This will see electrically heated buildings obtain improved EPC ratings.

The graph shows from 2005 SAP for grid supplied electricity had risen significantly but for the new version of SAP 10.2 this has reduced to 0.139 kgCO2/kWh. This is due to the decarbonisation of the electric grid over the last 10 years to fit with the governments approach to incentivising electric forms of HVAC.

Building Foundation Area


It is a requirement in iSBEM v6.1v to enter a foundation area. This value has no effect on the EPC. Failure to enter a correct value can present problems for the EPC calculation.

Project Database Changes

Within the project database walls, floors, doors and glazing have been simplified. Therefore, some categories are no longer available and have been adapted to be incorporated into new categories to represent entities common is most buildings.

Internal Walls:

All internal wall types can be found in the ‘Partition Wall’ section of the library

Included in the new version v6.1b there are more options to differentiate between insulated and non-insulated walls.

E.g If there is a cavity wall adjacent to an unheated corridor and there is no evidence of it being insulated. The correct selection would be ‘Internal Wall-Cavity (Uninsulated)’.

Suspended Floors

Suspended ground floors and exposed floor selections have been merged into one selection.


Some of the glazing options have been rationalised and some options such as 4mm single glazing no longer appear in the library option. In this instance assessors would use the inference procedure to select the glazing option.

Building Services Changes

Two new HVAC systems have been added:

1. Variable refrigerant flow (Only when includes mechanical ventilation)
2. Chilled ceilings or passive chilled ceiling beams and mixing ventilation

Light Plant Rooms- Zone without HVAC

Light plant rooms must always be assigned ‘’Zone without HVAC’’. Convention 10.07 does not apply to light plant rooms. The calculation will not run if a heating system is assigned.


When using the conversion tool to produce reports on the new version of the software the Project Database/Geometry foundation area must always be checked before a report is lodged. This is to be reviewed as the modelling may have been adjusted with the new entries on the database.

Green Zone Surveys (UK) Ltd currently uses DesignBuilder SBEM v7.1.2 which uses calculation engine SBEM v6.1.c.0



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