Note that the useful floor area as reported in an EPC certificate is not the actual property floor area.
This post talks about the main differences and the reason why whilst different both are valuable!
The main difference between the EPC floor area and property or gross floor area is in the definition.
EPC useful floor area: is the area where heating and cooling is taking place, that is where energy is being consumed to condition the space. By definition, the EPC useful floor area is measured up to the internal wall surfaces and excludes unheated spaces such as garages and washrooms accessible only from outside. The EPC floor area is used by the EPC calculation software for expressing the calculated annual energy and carbon emissions per unit of conditioned floor area. This is particularly useful for comparing the property’s EPC rating against other properties and/or benchmarks.
Gross floor area: defines the ownership area of a building. By definition gross floor area includes the full thickness of external walls as well as half the thickness of party walls. Gross floor area includes all internal and useable external spaces such as balconies and terraces. Gross floor area may be useful for property valuations and for determing compliance against planning policy such as the minimum area requirements based on the number of bedrooms in dwellings.
Example: To illustrate the difference in floor area let’s consider an example of a property having an external perimeter wall of 20m and a party wall perimeter of 40m. Assuming a wall thickness of 23cm then using the definitions described above the EPC useful floor area will be 9.20 sqm less than gross.