Introducing the Home Energy Model.

For more than three decades, SAP has been the standard methodology used to assess the energy performance of new homes in the UK. However, as buildings become more complex and low-carbon technologies become more widespread, the limitations of traditional assessment methods have become increasingly apparent.

The Home Energy Model (HEM) is being introduced to address these challenges and provide a more accurate way of measuring how homes perform in the real world.

As the Future Homes Standard reshapes residential construction, understanding HEM is becoming increasingly important for developers, architects and design teams.

What Is the Home Energy Model?

The Home Energy Model is a new residential energy assessment methodology being developed to replace SAP.

Its purpose is to provide a more sophisticated and realistic representation of building performance by accounting for how homes actually use and consume energy throughout the year.

Where SAP relies on simplified monthly calculations, HEM uses dynamic simulation techniques to model energy performance in far greater detail. The result is a methodology designed to better reflect modern building design, emerging technologies and real-world occupancy patterns.

Why is SAP being replaced?

SAP has served the industry well, but it was developed in an era when residential energy systems were significantly simpler.

Today’s homes increasingly incorporate:

• Air source heat pumps
• Solar photovoltaic systems
• Battery storage
• Smart controls
• Advanced ventilation systems
• Improved building fabrics

Many of these technologies are not represented particularly well within traditional monthly calculation methods. As a result, there can be a disconnect between predicted performance and how buildings operate once occupied.

The Home Energy Model aims to close this gap by providing a more detailed and evidence-based approach to energy assessment.

The Home Energy Model VS SAP.

The biggest difference between SAP and HEM lies in the way calculations are performed. Rather than using monthly average assumptions, HEM uses dynamic simulation to model performance across shorter time intervals throughout the year.

This allows the methodology to account for factors such as:

• Weather variations
• Solar gains
• Occupancy behaviour
• Thermal mass effects
• Heating system responsiveness
• Renewable energy generation profiles
• Energy storage interactions

One of the primary drivers behind HEM is the growing adoption of low-carbon technologies. Heat pumps, for example, perform differently depending on outdoor temperatures, operating conditions and user behaviour. Similarly, the effectiveness of solar PV systems depends on generation profiles, building demand and energy storage capabilities.

HEM is designed to capture these interactions more accurately, helping designers understand the true performance of different solutions.

What will change for developers?

While HEM offers significant benefits, it is also likely to increase the level of detail required during the design process. Greater modelling accuracy typically requires more detailed information about building fabric specifications, heating and hot water systems, ventilation strategies, renewable technologies, occupancy assumptions and building geometry

As a result, design teams may need to engage with energy modelling and sustainability consultants earlier than they do today. The shift places greater emphasis on performance-led design rather than simply achieving compliance at the end of a project.

What the experts think.

Andrew Sadler, Director at Buildpass, said:

“The Home Energy Model offers an exciting opportunity. Those who embrace energy modelling early, invest in performance-led design and develop a clear understanding of emerging methodologies will be better positioned to deliver compliant, efficient and future-ready homes.” 

As the Future Homes Standard continues to drive change across the sector, HEM will play a central role in helping the industry deliver homes that are lower carbon, more energy efficient and better aligned with the realities of modern living.

For support on how to make your next development Future Homes Standard ready, get in touch with a member of the Buildpass team.