What’s the Difference Between Commercial EPCs and DECs?
For building owners and managers, understanding how your property’s energy performance is measured is more important than ever. Two of the most common certificates used across the UK are the Commercial/Non-Domestic Energy Performance Certificate (EPC) and the Display Energy Certificate (DEC).
Though they may sound similar, EPCs and DECs serve different purposes, reflect different types of performance, and are applied differently depending on your location in the UK. Here’s a clear look at what each certificate means, how they are used, and what changes are on the horizon.
Commercial EPCs Explained
A Commercial or Non-Domestic EPC displays the energy performance of a building using an A+ to G scale, where A+ indicates a net zero carbon building and G represents the least efficient. This rating is calculated by assessing the building’s fixed characteristics such as insulation levels, glazing, heating systems, lighting, ventilation, and air conditioning.
EPCs are based on standardised assumptions about occupancy and usage patterns. They do not take into account how the building is actually operated, but rather how energy-efficient it is in principle, given its construction and services.
These certificates are required when a non-domestic building is constructed, sold or rented. Valid for 10 years, EPCs are produced by accredited Non-Domestic Energy Assessors (NDEAs) using approved methodologies (such as SBEM or DSM) and must be lodged on the national register. They are accompanied by a recommendations report suggesting practical upgrades to improve the building’s energy efficiency and reduce carbon emissions.
MORE INFORMATION > https://www.elmhurstenergy.co.uk/energy-certificates-for-non-domestic-buildings/
DECs Explained
A Display Energy Certificate (DEC) shows how much energy a building has actually used over the past year. It’s based on real data, like utility bills, and gives the building a rating from A (most efficient) to G (least efficient). This rating reflects how well the building is being run, rather than how it was built.
DECs are legally required in England, Wales and Northern Ireland for buildings that:
- Are used by a public authority
- Are frequently visited by the public
- Are larger than 250 square metres
Buildings over 1000m² must update their DEC every year. Smaller buildings between 250m² and 1000m² must renew theirs every ten years. An Advisory Report must also be provided, valid for seven years, which suggests practical ways to save energy based on how the building is performing.
The certificate must be clearly displayed where the public can see it—usually in a reception or entrance area—to promote openness and encourage better energy management.
Unlike an EPC, which rates the building based on its structure and services, a DEC focuses on real-world energy use, making it especially useful for facilities teams and building managers.
A DEC assessment can be completed by an accredited DEC Assessor
DECs in Scotland
Scotland does not currently use DECs. Instead, public buildings over 250m² must display an EPC and produce an Action Plan that outlines how they will reduce carbon emissions. This system supports Scotland’s performance-based approach to long-term energy improvement but does not require annual updates or public display of operational data.
MORE INFORMATION > https://www.elmhurstenergy.co.uk/energy-certificates-for-public-buildings/
Future Developments
While current requirements for EPCs and DECs remain in place, changes are already underway in Scotland. The Scottish Government has confirmed a series of reforms to the way commercial EPCs are presented and assessed—changes which aim to provide clearer, more meaningful information to building owners and users.
While no immediate changes have been confirmed for England and Wales, the government has recently consulted on the future of non-domestic energy certificates. This includes proposals for:
- Making EPCs more operationally relevant
- Extending DEC-style requirements to other building types
- Better alignment with national carbon targets
As of May 2025, the government is reviewing consultation responses, and no changes have been formally announced as of yet.