In November 2023 the Department of Energy Security and Net Zero (DESNZ) released two consultations introducing a new energy rating methodology known as the Home Energy Model (HEM). The Home Energy Model is intended to replace the existing Standard Assessment Procedure (SAP) and will be used to calculate compliance with Building Regulations such as the Future Homes Standard and produce Energy Performance Certificates.

What is the Home Energy Model?

The Home Energy Model is a complete replacement for the current Standard Assessment Procedure. It is a new methodology created using modern industry standards and is being validated against real-world performance data.

Like SAP, the Home Energy Model will underpin a large number of government policies, making it a key tool in delivering the UK’s housing and climate objectives. As described in the government consultation of the same name, it is ‘a new name for a new methodology’.

Initially developed by the Building Research Establishment (BRE), the Home Energy Model is now being taken forward and developed by Sustenic.

What are wrappers?

The Home Energy Model represents a next-generation approach to measuring home energy efficiency. However, in order to utilise the core HEM calculation engine (also called ‘full’ HEM or the Calculation Engine) for a specific purpose, a wrapper needs to be applied.

💡 Wrappers define the purpose the Home Energy Model in a particular context. Wrappers adapt the user inputs, input assumptions and output metrics, in order for it to be used for specific tasks. Each wrapper tailors the HEM core differently depending on the intended use.

The only wrapper currently in development is for compliance with the Future Homes Standard, although further wrappers are expected — such as for the production of EPCs.

Is the Home Energy Model available to use yet?

Despite the increasing discussion surrounding HEM, there is still confusion about its status. HEM is not yet a functioning tool in real-world settings. As the Future Homes Standard has not yet been finalised, the corresponding wrapper is not available. Until then, the Home Energy Model remains in development and is not currently in use.

Why HEM isn’t Drive-Ready (Yet) – A look under the bonnet

It’s a complex topic, so we’ve created a handy analogy to help you understand how HEM works and the role that Elmhurst play. Think of the HEM ecosystem as a car:

Raw HEM Engine = The car engine

This is the Government’s high performance engine – the core energy calculation logic. But on its own, it doesn’t move.

Wrappers = The Car Body and Components

These are the shells that make the engine usable, such as the car’s body, steering wheel, pedals, and gearbox. They turn raw energy and calculation into practical, tailored tools. Wrappers will be developed by Government and schemes will be able to connect to them to extract the correct data for specific tasks.

One wrapper might be for Future Homes Standard. Another wrapper for EPCs. Others could emerge for different needs.

Elmhurst = The Mechanic

We’re the ones in the workshop, building the vehicle around the HEM engine:

Using Energy Calculation as a Service (ECaaS), we connect to the right wrapper (FHS, EPCs, etc.)
Then, we build the user interface – the dashboard, buttons and controls so it’s simple to use, accurate and fully compliant.

But we don’t just build it and hand it over, we maintain it, update it, and ensure it’s roadworthy every time you drive. We work closely with government to understand every component and test rigorously, so when you start the engine, you know it will just work.

You = The Driver (& Navigator)

You’re the one in the driver’s seat, using the car we build and navigating day-to-day challenges within the industry.

But you’re not just driving, you’re helping us shape the vehicle. Feedback from Elmhurst members tells us what’s running smoothly, what needs a tune-up, and where the system can work better for real-world assessors, builders, and clients. You highlight the features that matter most and challenge us to make them better and more suitable for you.

The Rules of the Road

Just as every driver must follow the rules, like speed limits and traffic lights, our industry relies on conventions and regulations to ensure assessors consistently deliver work of the highest standard. As the industry’s leading Government-approved scheme, Elmhurst are here to guide you every step of the way through expert support and thorough auditing. We don’t just help you understand the rules, we make sure you’re applying them with confidence and consistency.

What is SAP 10.3?

While the Home Energy Model and the Future Homes Standard wrapper are still under development, the Government has committed to releasing the Future Homes Standard in 2025. Given this timeline, there were concerns about relying solely on the Home Energy Model for compliance.

In response, DESNZ and MHCLG announced in May 2025 that an updated version of SAP, also known as SAP 10.3, will be used to demonstrate compliance with the Future Homes Standard. This provides a smoother transition and gives the industry time to prepare for the full implementation of the Home Energy Model.

When the Home Energy Model is deemed complete and ready to take over from SAP 10.3, there will be a phased transition in order to give the industry time to recalculate existing designs in the Home Energy Model with Future Homes Standard wrapper.

How are Elmhurst Preparing?

Just as we’ve done with every previous update to Building Regulations, we’re already working to ensure our members and industry are fully prepared for what the Future Homes Standard will bring. Our teams have:

Launched HEM Theory CPD courses available to book now (see below)
Planned targeted training for both SAP 10.3 and the Future Homes Standard
Commenced development of a brand-new HEM application using the Future Homes Standard wrapper
Worked to upgrade our Design SAP 10 software to incorporate SAP 10.3 changes – With more to come!

Home Energy Model: Future Homes Standard (Theory)

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Demystifying the Home Energy Model