How an on-construction EPC differs from an EPC on an existing home
An EPC on an existing home is produced from a survey using the reduced-data methodology, where an assessor infers construction from what they can see. An on-construction EPC is produced from the full as-built SAP calculation, where the construction is known because it was designed and recorded. That makes it more accurate, and it also means the rating is a direct consequence of decisions taken at design stage.
Why the rating matters commercially
Buyers, lenders and, later, letting agents all read the band. Two dwellings that both comply with Part L can sit in different bands, and on a scheme of repeated types the difference usually traces back to heating strategy, glazing or a services choice made months earlier. If a target band matters to your sales strategy, say so at design stage, when it can be modelled cheaply, rather than at handover, when it cannot be changed at all.
Timing around handover
Certificates come after the as-built evidence is settled, because a certificate issued from a model that then changes has to be re-issued. On a phased site we lodge plot by plot as each is completed and tested, so sales are not held behind the last plot on the site.
