Home Energy Model Launch Delayed: SAP 10.3 Remains the Sole Approved Methodology

On 8 June 2026, the government updated its Standard Assessment Procedure guidance on GOV.UK to confirm that the launch of the Home Energy Model has been delayed. The government says the decision was taken during final internal assurance to make sure the model is “as robust as possible” when it goes live. For now, SAP 10.3 remains the sole approved methodology for demonstrating compliance with the Future Homes Standard, with HEM expected to follow “in the coming months”.

What the Government Said

The update appeared as a revision to the long-standing SAP guidance page rather than a standalone announcement. The relevant passage reads:

In the final stages of internal assurance, we decided to delay the launch of the Home Energy Model (HEM) to ensure that when it does go live, it is as robust as possible and delivered to the highest possible standard. This means that HEM has not launched at the same time as the Future Homes Standard (FHS) and SAP 10.3 is currently available as the sole approved methodology.

The guidance adds that HEM “will be introduced as the methodology for demonstrating compliance with the Future Homes Standard alongside SAP 10.3 in the coming months”, with final preparations “focused on guidance, assurance and readiness across the sector”. No specific launch date was given.

A Window That Has Now Passed

The significance of the timing is easy to miss. The Future Homes and Buildings Standards Consultation Response, published on 24 March 2026, set out a phased adoption plan: SAP 10.3 would be the only approved methodology at launch, and HEM would be approved “once it meets the full criteria”, expected no earlier than three months after publication, that is, no earlier than June 2026.

By that schedule, mid-June 2026 was the earliest point HEM could have appeared. The 8 June note confirms it will not arrive on that floor. In substance this is an incremental slip rather than a dramatic reversal, but it is the first time the government has explicitly used the word “delay” for the new-build methodology, and it attributes the cause to assurance and robustness rather than to policy or sector readiness.

Two HEM Timelines, Often Confused

Because both use the same engine, the new-build methodology and the EPC reform are frequently conflated. They are distinct:

The 8 June note is squarely about the first column. The EPC track, with its separate move to the four-metric certificate in the second half of 2027, is unchanged by it.

What This Means

For developers and builders, the practical effect is minimal. The Future Homes Standard does not come into force until 24 March 2027, and SAP 10.3 was always the methodology at launch, so the delay changes nothing about how a project is assessed today. Current work continues under Part L 2021 within the transitional arrangements.

For assessors and software vendors, the delay buys time. There is no immediate pressure to be operating HEM, and the ECaaS platform that delivers HEM calculations gains further runway for testing before it carries regulatory load. The trade-off is a shorter eventual overlap: once HEM is finally approved, the guaranteed dual running period of at least 24 months with SAP 10.3 starts later, compressing the window in which the sector can migrate at its own pace before SAP 10.3 is eventually withdrawn.

The broader signal is one of continued caution. HEM is a far more detailed, half-hourly model than SAP, and the government's repeated emphasis on assurance suggests it would rather ship late than ship a methodology that produces results it cannot stand behind.

What to Watch

• The “coming months” window: a concrete HEM approval date, or further slippage, is the headline item to track
• Summer 2026: the government separately committed to agreeing a launch date and shared implementation plan for reformed EPCs with industry and the devolved administrations
• ECaaS readiness: the move from limited beta to full production availability remains the practical gate for HEM at scale
• Assessor readiness: the assessor-facing software and HEM training programmes are still in development, with the accreditation schemes targeting readiness ahead of the FHS coming into force in March 2027. A route the wider workforce can actually use depends on this as much as on the methodology being approved
• HEM: EPC consultation response: still outstanding after the consultation closed on 18 March 2026

We track each of these on our Timeline & Status page, updated as milestones are reached.

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