Energy Performance Certificates (EPCs) are currently valid for up to ten years throughout the UK.  However, some schemes reduce this period significantly so more frequent assessments are required.
It can also be an advantage to the building's owner to have a more recent assessment.  This is particularly true where energy efficiency improvements have been carried out that are not reflected in the current certificate.  Where buildings are tenanted, it can also make life easier for a landlord if assessments are renewed at strategic points within the tenancy cycle.