A Level 5 EPC is an Energy Performance Certificate produced using dynamic simulation modelling (DSM).
Non-domestic EPCs are split into assessment levels according to the calculation method used. In simple terms, this means the type of energy model used to calculate the building’s energy performance.
For Level 3 and Level 4 EPCs, this is generally SBEM, the Simplified Building Energy Model. Level 5 uses DSM, or dynamic simulation modelling.
So what is the difference?
DSM vs SBEM: dynamic or steady state?
The main difference between SBEM and DSM is how they represent what happens inside a building over time.
SBEM uses a simplified, quasi-steady-state calculation method. Quasi-steady-state means the calculation treats conditions as broadly stable over each calculation period rather than modelling every hour individually. Weather, heat gains and heat losses are brought together through monthly energy calculations.
For most buildings, this provides a perfectly adequate way of calculating energy performance.
DSM, or dynamic simulation modelling, works differently. The building is simulated in short time steps, typically hourly or finer, across a full year of weather data.
Instead of calculating one overall energy balance for January, for example, a dynamic model can calculate what is happening at 9am on 14 January, then calculate it again at 10am as the weather, occupancy, solar gains and building conditions change.
This becomes important when a building contains features that change with time, or where heat is stored and released later. In those cases, averaging the behaviour over longer periods can remove some of the behaviour you are actually trying to model.
So how do I know which EPC level I need?
The assessment level is based on what your building actually contains. You work through the building’s features and services to establish the minimum level required.
Level 3 is for relatively simple buildings with straightforward services. These buildings do not have air conditioning or mechanical ventilation served by a central air-handling unit.
Level 4 is used where the building has more complex mechanical services. This can include centralised ventilation, air conditioning, VAV systems, fan coils, chilled beams and higher-temperature heating distribution.
Level 5 is required where the building contains specific features that the simplified Level 3 and Level 4 calculation method cannot represent. These are explained in more detail below.
Level 4 is also the minimum level for Building Regulations compliance assessments, including new-build assessments, however simple the building itself may be.
What exactly triggers a Level 5 assessment?
Only three features make a Level 5 assessment mandatory under the assessment-level decision flowchart. If any is present to any degree, Level 5 is required.
Automatic blind control refers to internal or inter-pane motorised blinds that respond automatically to solar gain, glare or daylight levels. The blind position changes through the day as conditions change, so the amount of solar gain entering the space depends on what the blinds are doing at that particular time. A monthly calculation cannot represent that behaviour in the same way.
Atria are large internal volumes, often spanning several floors and connected to surrounding occupied spaces. Warm air can rise through the space, temperatures can vary from floor to roof, and air can move between the atrium and adjoining areas. These conditions can change throughout the day and cannot always be represented by treating each area as a separate averaged zone.
Ventilation with enhanced thermal coupling to the structure means supply or ventilation air is passed through or across significant areas of exposed thermal mass, such as ventilated hollow-core slabs. The structure absorbs heat and releases it later. That time lag is an important part of how the system works, so it needs a calculation method that can model changes over time.
What links all three? They are time-dependent. That is why they need a method that models time.
Features such as VAV, fan coils, chilled beams, demand-controlled ventilation, night ventilation and centralised air handling do not by themselves trigger Level 5. They can be assessed at Level 4.
All three involve conditions that change over time, which is why a monthly calculation cannot fully represent them.
“To any degree” is important here. Automatic blinds in only a few areas of an otherwise ordinary building can trigger Level 5 for the whole assessment.
You can go up, but not down
Level 5 is the highest assessment level, but that does not mean it can only be used for buildings that require it.
A Level 5 assessment can be used for a building that would otherwise only require Level 3 or Level 4. The reverse does not apply. If the building contains a feature that requires Level 5, a Level 3 or Level 4 calculation cannot be used instead.
Level 5 can also be chosen where it is not mandatory, particularly for buildings with unusual geometry, mixed occupancy patterns or complex mechanical systems where dynamic simulation may represent the building more effectively.
What it means in practice
Level 5 assessments are carried out using approved dynamic simulation software. Examples include IES VE and DesignBuilder.
The assessment level is recorded on the certificate when the EPC is lodged.
Because dynamic simulation takes longer, requires more input data and takes more experience to carry out well, a Level 5 EPC will generally cost more than a Level 3 or Level 4 EPC for an equivalent building.
Sources and further reading
- Non-Domestic EPC Conventions for England & Wales, Assessment Level Decision Flow Chart
- NCM Modelling Guide, 2021 edition, England
- Approved Document L, Volume 2: Buildings other than dwellings
- CIBSE Certification, non-domestic EPC guidance and assessor requirements
→ How much does a Level 5 EPC cost?
Contact us if you have any questions about the content of this article.