New minimum evidence rules for energy assessors took effect on 1 October

2 October 2026

Quick answer: The Energy Assessor Scheme Operating Board (EASOB) has published minimum evidence requirements for energy assessors in England and Wales, effective 1 October 2026. For on-construction domestic assessors (OCDEAs) the list includes the software data file, plans, construction specification, U-value calculations, a developer as-built sign-off, the airtightness test certificate, psi-value documentation and photographs where Building Regulations require them. The guiding principle is that an auditor must be able to reproduce the EPC from what you hold.

What has been published

EASOB has issued separate minimum evidence documents for each assessor type — DEA, NDEA and OCDEA, with DEC and ACEA documents alongside. They are dated September 2026 and apply from 1 October 2026. At the time of writing the EASOB site shows the DEA document at v1.1 and the OCDEA document at v1.2, so check the live versions before relying on a printed copy.

Each document is explicitly a minimum list. EASOB notes that further evidence may be needed depending on the property, so treat it as a floor, not a ceiling.

What OCDEAs need on file

For a new-build SAP assessment the OCDEA document lists:

• the software data file submitted with the EPC lodgement;
• plans — floor plans, sections and elevations to support geometry, plus a site plan showing orientation and overshadowing;
• the construction specification;
• U-value calculations — for solid elements to BR 443 and BS EN ISO 6946; for windows to BS EN ISO 12567 or 10077, or BFRC certificates where applicable;
• an as-built sign-off — a statement from the developer (or whoever is the client for construction) confirming the building matches the design, and flagging any discrepancies;
• the airtightness test certificate;
• thermal bridging details — the psi values used, either from a published scheme or calculated to BR 497;
• photographic evidence where the relevant Building Regulations version requires it.

What DEAs need

The DEA document asks for floor plans in metric to two decimal places with areas, windows and heat-loss/party walls identified; site notes covering age, construction, heating and the reasoning behind decisions; and photographs of elevations, construction, insulation (with measured thickness), windows, doors, lighting, heating, hot water, ventilation, renewables and meters. Documentary evidence can substitute for a photograph where one cannot reasonably be taken, but it must be property-specific and independently verifiable, in line with RdSAP Convention 9.02. NDEAs have an equivalent list built around annotated zoning drawings and supporting calculations.

Why it matters for new-build work

Two lines in the OCDEA list deserve attention. First, the as-built sign-off puts a document from the developer in your file; if you do not already collect one on every plot, start. Second, psi values must be traceable: a published-scheme source or a BR 497 calculation, not a number typed into the software. That sits squarely alongside the direction of travel in the Home Energy Model, where a single blanket thermal bridging number is being removed. Junction-level evidence is becoming the norm in both worlds.

What to do now

Check your current file template against the OCDEA list, and chase developers for sign-offs and airtightness certificates before lodging rather than after. Where junction psi values are bespoke, make sure the calculation is on file and can be reproduced. Our guides on psi values and thermal bridging explain what an auditor will expect to see.

If you need a BR 497-style junction calculation for the evidence file, ΨMonkey models it free on screen and produces a Building Control-ready PDF.

Sources: EASOB minimum evidence requirements; OCDEA Minimum Evidence Requirements (PDF); DEA Minimum Evidence Requirements (PDF); Energy Trust summary.