Commercial and Domestic EPC differences

With Energy Performance Certificates, both Residential and Commercial, finally bedding in and becoming more widespread people often ask me “What is the difference between a Residential and Commercial EPC?” and, of course, why it is more expensive.

As I always try to explain to people the difference between the two is the level of detail required. A Commercial EPC is more akin to a Commercial Survey and requires the assessor to be more technically qualified and to be able to analyse equipment ratings from site.

For example, in a Domestic EPC on a standard two storey, three bedroom semi detached house, the assessor would likely be on site for approximately one hour. During that time they should take photographic evidence, measure the size of the building (internal or external) to achieve the size of the house, take the room height measurements, check the construction (floors, roof and walls), check for low energy lighting, look in the loft, look for insulation and energy improvement measures, and visually check the heating system, hot water system and any secondary heating. This is purely a visual inspection. Offsite the EPC will take approximately an hour to process.

Taking the same building and inspecting as a Commercial EPC is a similar process but far more intensive, lasting potentially over two hours on site. Taking one room as an example, this is the level of detail required in a Commercial EPC.

General building considerations

Such as orientating the building with a compass, what is the air pressure testing for the property. What power usage does the building have?

Photographic evidence

Taking photographic evidence of each feature and doing a drawing or double checking drawings provided.

Measuring each envelope

Measuring the height and length of each wall, the floor and ceiling.

Identifying the construction

Identification of each envelope, taking measurements to provide evidence of the type of construction, whether there is insulation in each envelope. For example, is an internal wall a partition wall or curtain brick? Has the partition wall been insulated? What building regulations dates apply to these constructions? If there is a false ceiling, what is above it?

Is the space that the envelope borders onto external?

  • Unheated?
  • Heated?
  • Each envelope construction type and what type of area the envelope borders onto must be identified.

Is there glazing in the room?

  • What type of glazing?
  • What type of frame does it have?
  • What are the height and width measurements?
  • What is the width of the actual glass?
  • If double glazed what is the width between panels of glass? Is the in between section air or argon filled?
  • Is the glass low e?
  • Are there methods of solar shading, such as blinds, or tinting?
  • Does the amount of glazing produce a daylight benefit area to the room?
  • What date/building regulations was it installed under?

How is the room heated or cooled?

The assessor has to identify the type of heating and cooling in the room and also the kind of boiler or plant equipment (such as for air-conditioning) that generates this. The assessor needs to correctly identify the make and model of the equipment as well as taking notes of the efficiencies and kilowatt inputs and outputs of the equipment and when it was installed. The method of control of the system, including methods of timing, must also be identified. The assessor must also undertake reasonable research off site to try to identify any information including any efficiency credits that it may have that could not be established on site.

Is the room served by mechanical supply and extract?

  • What type of system is this?
  • Is it just a local toilet fan, or covering equipment, or is it global building system?
  • What is the flow rate of air in/out of the system?
  • The assessor needs to identify the make and model, and conduct research off site too.


  • How is the room lighted?
  • What type of light bulbs? If mixed types, what is the majority?
  • What are their efficiency ratings?
  • Are there occupancy sensors, or is the lighting manually operated?

Domestic Hot Water

  • How is this provided?
  • How does this come into this room?
  • What type of system is it?
  • Is there storage?
  • Is this a local hot water system or a global one?
  • The assessor needs to correctly identify the make and model, as well as conducting off site research into the unit to identify efficiencies and whether it benefits from energy credits. The assessor also has to correctly identify how the hot water comes into the zone and the length of the dead leg.

What energy efficiency measures are in place?

What methods are applicable or appropriate for the room or the building as a whole?

This is just a snap shot of the level of detail required for one room and would have to be repeated for each room, along with for the building as a whole. If a Commercial EPC on this example building might take two or more hours on site, off site it could take a day or more to interpret all the data collected and to input it into the relevant software to model the building, as well as conducting the research that is needed.

Although they are called similar things, the Residential EPC and the Commercial EPC are different entities requiring different levels of technical knowledge and expertise. I have often been on site for both types of EPC and have been on site for longer than a surveyor is. A qualified Commercial Energy Assessor is an expert in their field and a professional who requires specialist skills and qualifications.

These are the essential differences between the two Energy Performance Certificates and explain why there is a difference in costs.

Written by Symon Silvester

One Response to “Commercial and Domestic EPC differences”

  1. steve morrin Says:

    we have an integrated house and shop and not sure what type of epc we need. the shop only takes up 24% of floor area

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