Guidance · 4 min
SAP calculation vs EPC: what is the difference?
How the design assessment, as-built calculation and new-dwelling certificate relate.
SAP is the calculation methodology
SAP is the government methodology used to estimate the energy performance of dwellings. For new homes it supports Part L assessment and provides the basis for the completed dwelling's energy rating.
The EPC is a certificate
A new-dwelling EPC is produced from the completed assessment and lodged by an appropriately accredited assessor. It is not the same process as a reduced-data survey of an existing home.
Design stage and completion
The design-stage calculation tests the proposed dwelling. At completion, the inputs are reconciled with the construction, evidence and test results before the as-built outputs and EPC are produced.
Why continuity helps
Keeping the assessment coordinated through design and construction makes it easier to manage substitutions and gather the correct completion evidence.
Building Regulations guidance and assessment methods can change, and transitional provisions may apply. Confirm the correct route for the particular project rather than relying on a general article.