Modeling the Future Homes Standard: SAP 10.3 and the New Home Energy Model

The UK Government (DESNZ) has confirmed that compliance with the Future Homes Standard (FHS) will be possible using either SAP 10.3 or the new Home Energy Model (HEM 1.0).

We think this dual approach makes sense. SAP 10.3 provides a familiar option while HEM lays the groundwork for the future. But for energy assessors and housebuilders, this raises an important question: which should you prepare for?

At Vulcan, we believe HEM offers long-term advantages that make it worth adopting early. Here’s why, and what it means for your day-to-day work.

For energy assessors: improve advice, future-proof your skills

HEM provides higher-resolution outputs and more realistic energy profiles. That means:

• You can explain why one design performs better than another.
• You can run sensitivity checks for clients: how does performance change if occupancy shifts, or the heat pump sizing is altered?
• You avoid having to retrain again later when SAP is phased out.

Assessors who get comfortable with HEM early will be able to deliver deeper insight, stand out in tenders, and meet future regulatory requirements sooner.

For housebuilders: de-risk compliance, unlock better specs

HEM models energy use more accurately. This matters because:

• High-performing designs (good fabric, smart systems, or orientation-led solar gains) are more likely to pass without over-specification.
• You can test multiple design options in the same framework used for compliance.
• You can identify cost-effective changes that improve headline metrics like Delivered Energy or Energy Use Intensity (EUI).

Builders who align early with HEM will have fewer surprises as the regulations shift. They can also use HEM outputs to demonstrate quality to customers and funders.

HEM offers a better model of the real world

SAP calculates building performance on a monthly basis. HEM runs on a half-hourly timestep, letting it capture time-sensitive effects like solar gains, storage behaviour, and heat pump performance under different loads. This matters for homes that use smart technologies or aim to reduce peak demand.

HEM also adopts a modular structure. Each component (heating, ventilation, etc.) can be independently updated or swapped. That makes the model easier to improve over time and better equipped to recognise new technologies as they emerge.

Better feedback for better homes

Because HEM simulates conditions more realistically, it can give design teams more meaningful feedback. A home with well-planned shading, solar generation, or high thermal mass will see the benefits reflected more clearly. SAP tends to average these out.

The result: HEM is more likely to recognise good design choices, and to guide better ones.

Useful advice, not just compliance

HEM outputs more useful metrics. For example, it reports total delivered energy and energy use intensity (EUI), which relate more closely to bills and practical performance. It also enables non-compliance models, which can test how designs perform under different occupancy patterns or weather years.

That means assessors using HEM can go beyond ticking boxes. They can help clients make better-informed decisions.

Preparing for the future

SAP 10.3 is a stopgap, and the long-term plan is for HEM to replace SAP entirely.

Yes, there will be a learning curve. But assessors who adopt HEM early will be better placed to support clients, differentiate their service, and shape the industry as it evolves.

Our take

At Vulcan, we support a fast rollout of the Future Homes Standard. We think HEM is essential to making that rollout meaningful.

While both SAP and HEM will be valid routes to compliance, they won't be equal. HEM will help assessors deliver more accurate assessments, better design advice, and higher-performing buildings. That’s why we’re preparing for HEM now, and helping our users do the same.

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