How Vulcan handles SAP
With the government response to the Home Energy Model (HEM) consultation now published and the dual-route Future Homes Standard (FHS) confirmed, we'll soon enter a transition period where both HEM and SAP 10.3 can be used to demonstrate compliance for new home designs.
SAP 10.3 exists to de-risk this transition: it's an incremental update to the familiar SAP 10 methodology, tuned for the Future Homes Standard, while HEM is still bedding in as the new, half-hourly model.
In practice, that means assessors and housebuilders will be asked to understand – and often use – both methods in parallel.
Vulcan's view is simple
- HEM should be the primary tool for designing and assessing low-energy, low-carbon homes.
- SAP 10.3 will still matter in the short term: clients, lenders or energy companies may care how designs look under both methods.
- The worst outcome is doing twice the work just to get two sets of numbers.
Why HEM should come first
HEM has been designed to replace SAP. It models energy use half-hourly instead of monthly and is better suited to:
- modern heating systems (especially heat pumps + smart controls),
- on-site generation and storage, and
- emerging tariffs and flexibility services.
That extra granularity should make it better at recognising genuinely efficient, flexible designs – and gives assessors more levers to pull when they're trying to help a client design a better building, not just "pass compliance".
So we think the starting point for FHS projects should be: build a robust HEM model first.
The practical problem: two methods, two data entries
In reality, assessors will not drop SAP overnight. Housebuilders and other stakeholders (lenders, energy retailers) may want to see SAP and HEM side-by-side, to calibrate new results against what they've seen before.
Other Energy Assessor schemes have indicated they will focus on updating their existing Design SAP tools and add HEM as a second piece of software.
That last point is the operational killer: if SAP and HEM live in separate tools, with separate input flows, assessors will end up:
- drawing or describing the same building twice,
- keying in similar data twice,
- and managing the risk the two models drift apart.
That's wasted time and additional error risk with no benefit to the client.
Vulcan's approach: design once, compare HEM and SAP 10.3
Vulcan is built around the Home Energy Model from the outset. From a single HEM model, we now:
- generate a SAP 10 XML instantly, with no extra inputs, and
- will surface SAP 10.3 results in the software once the final methodology and test cases are published.
In practice, that means:
For energy assessors
- You build one high-quality HEM model in Vulcan (using the visual editor or imports).
- Vulcan produces a HEM result, plus a SAP 10 XML file ready for use with your SAP calculation engine of choice.
- Once SAP 10.3 is final, you will see both HEM and SAP outcomes from the same inputs, without double entry. For this we will use a SAP 10 calculation engine tested against official SAP 10.3 test cases.
For their clients: housebuilders and homeowners
- You get consistent, comparable numbers: one underlying model, two methods.
- You can see where HEM rewards better design choices (fabric, systems, controls) and how that compares to SAP.
- You reduce the risk of "which model is right?" arguments mid-project because you know both are fed from the same inputs.
- Your assessor spends more time on design options and less time on retyping data.
The script that generates a SAP XML from HEM inputs is already available to early adopters on request and will be exposed as a simple toggle for the browser app and MCP server in this week's release.
Vulcan: One model, two methods, less work
Vulcan believes the Home Energy Model is the future. This is because we believe:
- HEM is the best foundation for designing genuinely low-energy, low-carbon homes.
- A high-quality, audited HEM dataset is the best basis for improving buildings and policies over time.
- SAP will remain part of the picture for a short while, but it should not dictate how we design homes for the next 20 years.
If you’re an energy assessor or housebuilder, the practical move is simple: build and maintain one high‑quality HEM model per project, and let Vulcan generate SAP outputs when you need them. Don't duplicate work, and build a HEM dataset that will still be useful in five years' time.