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The new EPC: HEM and the four-metric assessment, for assessors

The biggest EPC methodology shake-up since 2007 is now delayed to H2 2027. What DEAs and OCDEAs need to know about HEM, the four new metrics, and pricing.

For Domestic Energy Assessors (DEAs) and On Construction Domestic Energy Assessors (OCDEAs) — the biggest shake-up of the EPC methodology since its introduction in 2007 is now confirmed, and the timeline has slipped. Here’s what’s changing and when.

What’s replacing SAP and RdSAP

The Home Energy Model (HEM) is the new assessment methodology. For existing dwellings, RdSAP is being replaced by what’s being called HEM:EPC (some commentators are using HEMEX). For new builds, HEM will sit alongside SAP 10.3 during a transition.

The four new headline metrics

The current single A–G rating is being replaced by four:

  1. Fabric Performance — a fabric energy efficiency metric measured in kWh/m²/year, based on thermal properties of the envelope (walls, roof, floor, glazing, airtightness).
  2. Heating System — a metric reflecting the efficiency and carbon intensity of the primary heating system. Fossil-fuel systems will not achieve C or above on this metric — by design.
  3. Smart Readiness — a new metric reflecting the property’s capacity for smart controls, demand response and integration with low-carbon heating.
  4. Energy Cost — retained from the current methodology as secondary information to help occupiers understand running costs, but no longer the headline compliance metric.

For MEES purposes from 1 October 2030, landlords need to meet a compliance standard against two metrics: the primary Fabric Performance metric, and one of either Heating System or Smart Readiness (landlord’s choice).

The revised timeline (as of March 2026)

  • 21 January 2026: Warm Homes Plan published; partial response to the Energy Performance of Buildings consultation; HEM:EPC consultation opened.
  • 18 March 2026: HEM:EPC consultation closed.
  • 9 March 2026: Government confirms the launch of HEM-based EPCs has been delayed from October 2026 to the second half of 2027. The existing EER methodology continues in the interim.
  • Transition period: HEM and the current EER run in parallel. New EPCs issued during the transition will display both old and new methodology ratings.
  • 1 October 2029: EER methodology withdrawn. HEM:EPC becomes the sole assessment methodology for new EPCs.
  • 1 October 2030: MEES at EPC C (dual-metric) applies to all private tenancies in England and Wales.

What changes for the assessor on site

  • Assessment time: roughly 1 hour 40 minutes under HEM, versus around 20 minutes for a current RdSAP EPC. That’s a five-fold increase.
  • Data capture: a modular input framework replaces RdSAP’s rigid defaults. You record what you can directly observe; HEM applies calibrated defaults for what you can’t (e.g. hidden cavity insulation thickness).
  • Alternative inputs: government is consulting on allowing data from trusted sources (MCS certificates for heat pumps, Building Control records) via API. Not yet confirmed but likely in the final design.
  • More detailed data accepted: where a building survey or retrofit plan exists, the data can be fed into HEM for a more accurate result. This creates a continuum from basic EPC to full retrofit assessment on the same methodology.

What changes for your practice

  1. Pricing. A five-fold increase in site time against current RdSAP fees is not sustainable. Expect HEM:EPC fees to be materially higher — early industry estimates suggest 2–4x current RdSAP fees. Plan your pricing model now.
  2. Training and accreditation. Your existing DEA/OCDEA accreditation will not automatically transfer. Details from the accreditation bodies (Elmhurst, Stroma, Quidos, NES, Sterling) are expected closer to launch. Factor in training time and cost.
  3. Software. The current SAP/RdSAP software landscape will be replaced or substantially updated. The government is publishing HEM as open-source components via Git repositories; commercial software vendors will wrap these. Don’t commit to a multi-year software contract that doesn’t include HEM readiness.
  4. Equipment. HEM’s detail means more on-site measurement. LiDAR scanning for geometry, smart meter data integration (SMETER HTC estimates are being considered), and potentially thermal imaging as supplementary inputs. Not all mandatory, but the direction is clear.
  5. The transition headache. You’ll be issuing certificates under two methodologies in parallel from H2 2027 to October 2029. Clients will ask which one matters for their MEES compliance. The answer is: a property achieving EPC C under the current EER methodology before 1 October 2029 is grandparented and compliant until that EPC expires. After 1 October 2029, only HEM:EPC counts.

What this means for the advice side of your role

Landlords will increasingly come to you asking which improvements get them to EPC C on the new metrics. That’s a different conversation from current EPC recommendations — the Heating System metric effectively ends gas boiler recommendations for properties trying to hit C, which means heat pump knowledge, hybrid system knowledge, and retrofit sequencing become core skills. Assessors who can do this are going to be in very short supply against demand from 2027 onward.

The key unresolved questions (as of April 2026)

  • Exact band boundaries for each metric — the HEM:EPC consultation closed 18 March; government response expected later in 2026.
  • How the four metrics will be presented to consumers on the certificate itself.
  • Whether smart meter HTC data will be incorporated, and how privacy and data protection will be handled.
  • Transitional rules for EPCs issued in the 2027–2029 dual-running window.

References and further reading

General guidance for domestic energy assessors. The HEM methodology and launch timeline are still being finalised — always check the latest from DESNZ and your accreditation body.