SBEM vs DSM explained for commercial buildings
If you need an EPC for a commercial building, you may be told it needs a Level 3, Level 4 or Level 5 assessment. The level is not the EPC rating. It helps determine which modelling method is appropriate for the building and what level of assessor is required.
SBEM and DSM: what is the actual difference?
SBEM stands for Simplified Building Energy Model
It uses a monthly quasi-steady-state calculation. In practical terms, SBEM does not follow the building hour by hour. It takes the heat coming in, the heat going out and the energy needed to heat or cool the space, and works out the overall balance for each month using standardised weather and usage assumptions.
Example: take a glazed office in July. In reality, the room may be cool at 9am, warm up when the afternoon sun reaches the windows, need more cooling at 2pm and cool down again later. SBEM does not follow that sequence separately. It considers the overall effect of solar gains, occupancy, lighting, equipment, ventilation and July weather to calculate the month’s energy demand.
DSM stands for Dynamic Simulation Model
A DSM follows the building through much shorter time steps, typically hour by hour or at shorter intervals depending on the approved software. It can therefore represent the glazed office warming as the sun reaches the facade, the cooling system responding to the increased load, and the load falling again later in the day.
DSM gives a more detailed representation of how the building behaves, but that does not automatically make the EPC more accurate or produce a better rating. The result still depends on the quality of the inputs and how well the building and its systems are represented.
So what do Levels 3, 4 and 5 mean?
| Level | Method | In simple terms |
| Level 3 | SBEM | For buildings whose systems fall within the Level 3 assessment criteria |
| Level 4 | SBEM | Still SBEM, but covering the more complex HVAC and ventilation systems listed in the Level 4 criteria, including Building Regulations assessments |
| Level 5 | DSM | Dynamic modelling where Level 5 features are present or DSM is the appropriate modelling route |
For Level 3 and Level 4, iSBEM is the government-provided interface to the SBEM calculation engine. You still create the building model, define zones and enter geometry and systems, but it is not a dynamic 3D simulation in the same way as approved DSM software such as IES VE or DesignBuilder.
Which level does my building need?
The decision tree on the next page shows the main features that move an assessment into Level 4 or Level 5, including certain ventilation strategies, HVAC systems, atria and automatic blind controls.
Geometry can matter too
SBEM can be used for buildings of any size, but some forms and relationships between spaces can be difficult to represent without approximation. Where the geometry or interaction between spaces is particularly complex, DSM may be the more appropriate route even if the checklist does not tell the whole story.
Can Level 5 be used for a simpler building?
Generally, yes. An approved DSM can be used where SBEM could have been used, subject to the software’s approved scope and the assessor’s accreditation. But where Level 5 modelling is required, a Level 3 or Level 4 assessment should not be substituted.
How much does each level cost?
There is no useful fixed price for a Level 3, 4 or 5 EPC. Cost depends on the building itself: its size, number of zones, geometry, glazing, services, available evidence and the time needed to construct and check the model. A large or complicated Level 4 building can therefore cost more than a small Level 5 building.
Level 5 often takes longer because DSM models are generally more detailed and require more simulation setup, checking and review. For a straightforward building, SBEM is often the quicker and more proportionate route.
Use the decision tree below as a quick guide, then confirm the appropriate route with your accredited energy assessor or building energy consultant.
Sources: Non Domestic EPC Conventions for England & Wales, Issue 9; NCM Modelling Guide 2021 Edition (England); SBEM Technical Manual, UK Volume.
Download the PDF EPC Level Decision Tree below:
If you have any questions about the information on this page, or would like to discuss which EPC assessment may be appropriate for your building, please don’t hesitate to contact us here.