Future Homes need the Home Energy Model

I spoke to dozens of UK construction industry professionals at FutureBuild last week, to understand how well prepared they and their organisations were to adopt the Home Energy Model. Adoption of the Home Energy Model by UK domestic energy assessors and designers is critical to build healthy, comfortable and low cost UK homes.

The Home Energy Model (HEM) is a methodology to simulate the energy use of domestic buildings. The Home Energy Model will be used to assess new home designs against the Future Homes Standard from June 2025, and is due for use to create Energy Performance Certificates for existing homes from Q3/Q4 2026.

The Home Energy Model is much higher resolution than current energy modelling methodologies (with half hourly instead of monthly calculations and outputs). This enables HEM to more accurately predict the performance of homes,  identify lower cost approaches to design homes that are comfortable, low cost and healthy, and create a detailed baseline to evidence that buildings perform as designed or explain discrepancies. HEM’s calculations are also open source, enabling transparency and ongoing improvement.

The UK Construction Industry is locked in a cycle of last minute preparation

UK Construction professionals at FutureBuild, including building energy assessors, designers, suppliers and general contractors reported strong disincentives to prepare for new or updated domestic energy assessment methodologies.

New modelling methodologies are often delayed. For example, RdSAP 10 was originally due last year, but many at Futurebuild believed it was unlikely before this Summer. Training courses have a high upfront opportunity / financial cost, and delays to regulation can means further learning is required. This penalises businesses that prepare too early.

This unpreparedness has negative consequences:

• Missed Opportunity: Every month the Future Homes Standard is delayed, 10 to 20 thousand homes are designed without the benefit of HEM's higher resolution and accuracy. Each month HEM is delayed for Energy Performance Certificates for existing homes, 100 thousand assessments are conducted, each a missed opportunity to provide credible and actionable advice to make homes comfortable, healthy and low cost.  ‍
• More Delays: Private rentals (~20% of homes) need to comply with Minimum Energy Efficiency Standards. Landlords that see EPCs are being reformed may wait until the introduction of HEM based requirements so they can understand what they need to do. HEM may make investment into funded retrofits more efficient (~20% of homes), and improve decision making for private homeowner retrofits (~60% of homes).‍
• Worse Outcomes: Energy assessors that are not prepared for HEM (which requires more detailed inputs than SAP and delivers new and different outputs), will find it more difficult to answer client questions and deliver accurate assessments on time. Many professionals agreed a poorly managed move to SAP 10 in 2021 led to rework, delays, and stress.

Vulcan want to see this cycle broken

We need to ensure HEM is released on time, and improve incentives to prepare for this release. If we do not prepare, the Home Energy Model may be broken on release and not achieve its goals.

One historical cause of modelling methodology delay - the update process itself - has been resolved with the transition to the Home Energy Model. Updates to SAP and RdSAP (such as the move to RdSAP10) required the BRE (the Building Research Establishment) to publish a methodology, Energy Assessor Schemes to implement this in their own SAP engines, and BRE to validate test cases. For the Home Energy Model, the Ministry of Housing will provide an API that will be used by Energy Assessor Schemes (called “Energy Calculation as a Service” or ECaaS). Energy Assessor Schemes will "only" need to provide interfaces, training and quality assurance.

The biggest risk is a delay in development of the wrapper for the Home Energy Model to create Energy Performance Certificates for existing homes (the HEM:EPC wrapper). This is a large and complex piece of work. The HEM:EPC wrapper will involve a trade-off between assessment speed and accuracy, made more complex by the transition from SAP to HEM. Based on the proposed Energy Performance in Buildings reforms, the EPC wrapper will also add multiple new metrics for carbon, fabric energy efficiency, heating systems and “smart readiness”. This work is due to be completed for a Q4 2025 consultation.

1. Engage industry early to de-risk HEM:EPC delivery

To de-risk HEM:EPC delivery, the HEM development team can better engage the UK Construction Industry.

The MHCLG Energy Calculation as a Service Team - responsible for the building regulations HEM API - have effectively communicated their work through "show and tell" sessions and public API documentation. The team(s) that will further develop HEM and the EPC wrappers can learn from this approach. Engaging the construction industry can build trust in the accuracy of the wrapper and in its timely delivery. Early iterations of the EPC wrapper can help the HEM development team gather useful feedback on usability and accuracy.

While a consultation tool was made available to use the Home Energy Model (and limited to the Future Homes Standard), this has since been withdrawn - leaving a gap for the UK construction industry to understand HEM. Vulcan has stepped in to support professionals to use HEM with a web application and documentation.

More can be done here. For example, we are strong advocates for a public mechanism engage with the accuracy of the Home Energy Model and its wrappers. This can enable public contributions of HEM models for UK dwellings, and be directly integrated into the HEM codebase. A well designed platform for the public to engage with validation can encourage contributions to the HEM codebase and validation dataset, and accelerate HEM's improvement.

2. Make learning rewarding to improve HEM preparation

Today, most Energy Assessor training and CPD is paid. This creates a financial disincentive for early preparation that becomes obsolete or leads to duplication. To encourage preparation and continuous learning, Vulcan charge an affordable flat monthly or annual fee for Members that includes unlimited training. While we offer hands-on support to prepare Vulcan users to understand the Home Energy Model, we are investing in channels for self-service user learning from the product, documentation and peers.

Integrated training can be more relevant to a Member’s needs and context, and more convenient to schedule and consume. For example, Members assessing unfamiliar archetypes or heating systems could be supported "in the moment", and as a result produce a more accurate assessments. Integrated training also enables Energy Assessors to learn skills required to complete higher value and revenue work, without significant upfront costs.

Prepare for HEM with Vulcan

By making learning low cost to our users, and ensuring our user's feedback drives our product roadmap, we have been able to effectively support our early adopters to learn about the Home Energy Model.

We’ll run free webinar sessions in the coming weeks to enable more professionals to understand the changes coming with the Home Energy Model. If you and your organisation have questions, reach out to us at hello@usevulcan.app.