As the housing sector prepares for one of the biggest regulatory shifts in decades, we asked a simple question to our community: “What’s your biggest EPC reform unknown right now?”

• 50% want clarity on how the Home Energy Model (HEM) will score older stock

• 25% are unsure about what fabric performance thresholds will be

• 25% are questioning what “2030 vs 2039” actually looks like 
• 0% selected smart readiness (which, in itself, is interesting)

It’s clear there’s a need for understanding on the new Home Energy Model, so here’s how we’re making sense of it at Ecogee:

Older stock is the main question

It’s no surprise that the housing sector’s biggest concern is how HEM will treat existing homes – especially older stock. When we map archetypes against indicative heat demand, the gap becomes obvious.

While final thresholds aren’t final, industry modelling gives a good indication of where things are heading:

Housing Type	Typical Heat Demand	Likely Outlook
Post-1990 cavity wall	50–80 kWh/m²	Likely compliant
1930–1980 cavity wall	70–110 kWh/m²	Borderline
Pre-1930 solid wall	120–200 kWh/m²	High retrofit requirement

Home Energy Model (HEM) shifts the focus from cost to physical performance

SAP (the current system) is largely cost-based, meaning a property can score well, despite losing a lot of heat. HEM changes that by focusing on actual heat demand, fabric efficiency and system performance.

Put it this way – SAP asks “how expensive is it to heat?” and HEM asks “how much energy does this building actually need?”

Fabric first. Poor building fabric = low HEM score

For older homes, fabric performance is likely to determine whether a property passes or fails. External/internal wall insulation will become central followed by roof and floor upgrades, airtightness and detailing.

Heating systems still matter, but they won’t compensate for a buildings fabric.

This means that homes with high heat loss, particularly solid wall properties, will score significantly lower under the HEM model, unless the building fabric itself is improved.

So what does that mean in practice for housing providers? 

Get older homes HEM ready  

Reaching compliance on older homes won’t be a single intervention. It will require whole house planning (PAS2035) and carefully planned programmes of work.  

The key is to identify solid walls and “hard to treat” stock, model heat demand across archetypes and prioritise (as always) fabric first upgrades!

Where Ecogee can help: 

At Ecogee, we’re already working with housing providers to get homes, particularly old ones, ready for the changes by: 

• Mapping stock against likely HEM metrics 

• Identifying portfolio-level risk 

• Building practical, deliverable retrofit plans 

• Supporting delivery from assessment to handover 

Are you modelling your stock now, or waiting for final guidance?  

What’s been the hardest to pin down in your planning so far?