The Home Energy Model (HEM)

The Home Energy Model (HEM)

The future of energy assessment in the UK

The Home Energy Model (HEM) is a new government-backed methodology being developed to replace the Standard Assessment Procedure (SAP) used for assessing the energy performance of new homes in England.

In time, it is also expected to influence — or replace — how Energy Performance Certificates (EPCs) are produced across the wider housing stock.

While HEM is still being finalised, it represents a major shift in how building energy performance is calculated, reported, and regulated.

At Saxon Surveying, we’re actively tracking this transition so we can help clients understand what’s changing — and what isn’t — long before it becomes mandatory.

What is the Home Energy Model?

The Home Energy Model is a new calculation engine designed to provide a more realistic and detailed assessment of how homes use energy.

Unlike SAP, which relies on simplified assumptions, HEM is intended to:

• Better reflect real-world building performance
• Support the UK’s net zero objectives
• Provide a common methodology across regulations and future EPCs
• Be flexible enough to adapt as building technologies evolve

Initially, HEM is being introduced for new build compliance, but its scope is much broader.

Why is SAP being replaced?

SAP has been the backbone of energy assessment in the UK for decades, but it has known limitations:

• It uses fixed assumptions about occupant behaviour
• It struggles to reflect modern construction methods accurately
• It is increasingly disconnected from how buildings perform in practice
• It was never designed with net zero in mind

HEM is intended to address these issues by using a more dynamic, physics-based approach to modelling homes.

How is HEM different from SAP?

At a high level, the differences look like this:

Importantly, HEM is not just “SAP 11” — it is a fundamentally different way of assessing homes.

Who is HEM aimed at right now?

In its initial rollout, HEM is primarily relevant to:

• Self-builders planning new homes
• Architects designing low-energy buildings
• Builders and developers working under new Building Regulations
• Energy assessors producing compliance calculations

For existing homeowners and landlords, SAP-based EPCs remain the standard — for now.

Will HEM replace EPCs?

Short answer: eventually, yes — but not yet.

The government has made it clear that HEM is intended to become the core calculation engine underpinning future energy assessment frameworks. That likely includes EPCs in the longer term.

However:

• Current EPCs remain valid
• There is no immediate requirement for homeowners to act
• Any transition will be phased and consulted on

This is a long-term change, not an overnight switch.

What does this mean for homeowners and landlords?

Right now:

• EPCs are still produced using SAP/RdSAP
• Legal requirements for sales and lettings are unchanged
• Existing EPCs remain valid for 10 years

Looking ahead, HEM is likely to result in:

• More accurate EPC ratings
• Better alignment between EPCs and actual energy bills
• Stronger links between EPCs and retrofit decisions

How Saxon Surveying is preparing

As an experienced energy assessor working across domestic and commercial properties, we’re:

• Monitoring government consultations and updates
• Reviewing how HEM outputs will affect EPCs and compliance
• Preparing to support clients through the transition when it arrives

Our approach has always been practical, evidence-based, and forward-looking — and that won’t change.

Should you do anything now?

For most people, no immediate action is required.

If you are:

• Planning a new build
• Designing a low-energy home
• Working on long-term development projects

…then understanding HEM early is a real advantage.

For everyone else, the key is simply to stay informed — and that’s exactly why this page exists.

Need advice?

If you’re unsure how upcoming changes may affect your project, or you’d like guidance on EPCs, new builds, or compliance, feel free to get in touch.

We’ll always explain what matters — and ignore what doesn’t.