In the second half of 2027 the methodology behind every domestic EPC changes. The Home Energy Model, HEM, replaces RdSAP for existing homes, and with it goes the system of assumed default values that today's certificates lean on. For landlords the practical meaning is simple: the routes to an EPC C get harder from 2027, while anything lodged before then keeps its full ten-year validity.
What actually changes
| Today (RdSAP 10) | From H2 2027 (HEM) | |
|---|---|---|
| Unverified elements | Filled with age-band assumed defaults | Expected to be physically evidenced |
| Air tightness | One verified test can replace the default | Full evidence regime, more demanding |
| Primary metric | Single SAP score | Fabric performance first |
| Secondary metric | n/a | Heating system or smart readiness, landlord chooses |
| Gas boilers | Score within the single scale | Capped below the top band on the heating metric |
The fabric-first logic
The reformed rental standard measures the building envelope first: insulation, glazing, draught-proofing and air tightness. On top of fabric, a landlord satisfies one secondary metric, either the heating system, which in practice favours heat pumps since fossil-fuel boilers are capped below the top band, or smart readiness, which rewards solar, batteries and smart controls. Our 2030 guide works through which combination suits typical Lancashire rentals.
Why this creates a window, not just a deadline
Three dates line up. RdSAP 10 is in force now and accepts a verified air permeability test in place of the assumed default. HEM arrives in the second half of 2027 and closes that shortcut. And under the confirmed framework, a certificate lodged at C before 1 October 2029 is recognised until it expires, with EPCs valid for ten years from lodgement.
Put together: a mid-D rental corrected to a C this year through the measured route holds that C into the mid-2030s, straight through the deadline. The same property assessed for the first time under HEM faces a fuller evidence exercise, potentially with works attached, at 2029 market prices.
What to do with this information
- Check every certificate now for score, expiry date and "assumed" entries.
- Mid-to-high D properties: use the measured route while RdSAP 10 permits it, £500 flat, success-only, no building work.
- Properties needing real work: plan it against the fabric-first metrics so nothing is spent on measures the reformed EPC undervalues, and use the £7,500 grant while it is live.
- Renewing an EPC that expires around 2027 to 2029? Time it deliberately, an early renewal at C locks the easier methodology in.
Frequently asked questions
What is the Home Energy Model?
What happens to assumed values under HEM?
Will my existing EPC still be valid after 2027?
How do the reformed EPC metrics work?
Should I wait for HEM before doing anything?
Next step
Lock in a C under the current methodology
A C lodged now is valid for its full ten-year term. Thermova's measured route costs £500 flat and is charged only when the C is on the register. Ask the chat assistant to check whether your property qualifies.