The Energy Performance Certificate is the single number that follows a home around when it is sold or let, and it is being rebuilt. Two things have changed since this story first broke in January 2026: the reformed certificate carries four headline metrics rather than one, and the date it arrives has slipped. Both matter to anyone weighing up new windows, which is why the story sits near the top of our double glazing news and policy updates.
What the reformed EPC actually measures
The government set the structure out in its partial response to the consultation on reforms to the Energy Performance of Buildings regime, first published on 21 January 2026. Its words: “For domestic EPCs, we will replace the existing single cost metric with four new headline metrics: energy cost, fabric performance, heating system and smart readiness.”
Two further measures sit behind the headline four. The response confirms a secondary energy demand metric, “based on delivered energy, to provide information on modelled energy usage of a building”, and says government will “also retain a secondary carbon-based metric on domestic EPCs”. The old rating is not thrown away either: the legacy EER metric is retained “to enable comparison with current EPCs, and to support ongoing compliance with existing regulatory measures until it is no longer required”.
One point of care, because plenty of coverage has got this wrong. The four metrics are published as a list, without a stated ranking. Nothing in the response says fabric is scored first on the EPC. What it does say is that fabric performance is a headline metric in its own right, which is a different and more useful claim. If you want the technical side of how a window's heat loss is measured, our guide to U-values explained covers it.
The launch has moved to the second half of 2027
The reformed certificates were originally due in October 2026. They are not coming that soon. In an update dated 9 March 2026, GOV.UK said: “Government continues to work at pace to deliver reformed domestic EPCs. Following engagement with industry on the delivery timeline, we have decided to move the launch of the reforms to the second half of 2027. We will work with industry and the devolved administrations to agree a new launch date and shared implementation plan by the summer of this year.”
Read that carefully and you will notice there is still no fixed day in the diary. The second half of 2027 is the window, and the precise date was to be agreed with industry and the devolved administrations. Treat any firmer date you see quoted as unsourced until GOV.UK publishes one.
Where the 1 October 2029 date really comes from
You will find 1 October 2029 attached to the Home Energy Model all over the internet, including in an earlier version of this page, which we have corrected. The date is real. It simply belongs to a different rule.
It appears in the government response on improving the energy performance of privately rented homes, which sets out the Minimum Energy Efficiency Standards landlords face. That response says government will “allow for properties with a current EPC C to be recognised as compliant under the future standard until the EPC expires. This includes private rented homes graded C or above against the Energy Efficiency Rating (EER) on EPCs before 1 October 2029”.
In plain terms: if a rental holds a certificate issued before 1 October 2029 that grades it C or better on the old EER measure, that certificate keeps the property compliant with the tougher standard until it expires. It is a cut-off for honouring legacy-methodology certificates, not a switch-on date for a new calculation engine. For landlords that is worth knowing, because it means an early assessment has a shelf life rather than being wasted work. The deadline it protects you against is the one we cover in the EPC C rules landlords must meet by 2030, and our guide to double glazing for landlords works through how glazing contributes.
As for the Home Energy Model itself, it was consulted on from January 2026, with the consultation closing on 18 March 2026. No published source states a date on which it becomes compulsory, so we are not going to give you one.
Why fabric becoming a headline metric is good for glazing
Here is the part that actually changes the maths on a window quote. Under the existing single cost metric, a window upgrade is diluted into a running-cost estimate, competing with the boiler and the tariff assumptions for credit. When fabric performance becomes one of four headline metrics, glazing is scored on its own line instead of being buried in an average.
The private rented sector rules push in the same direction, and there the ordering is explicit. That standard is described as “a dual-metric standard as proposed in the consultation, with a fabric performance standard first followed by landlord discretion to meet either a heating system standard or a smart readiness standard”. In other words a landlord can choose between heating and smart readiness, but the fabric standard is not optional and cannot be bought off with a heat pump. Insulation, draught-proofing and windows are the unavoidable first spend.
Windows count towards fabric under both the current EPC and the reformed one, so glazing is a durable improvement rather than a bet on one version of the rules. Someone who upgrades this year is improving the part of the assessment that both systems agree on, whether their certificate is recalculated now or after the reforms land.
Homeowners chase a quick EPC point with a cheap fix, then find the rules had moved on by the time they came to sell. Fabric is the one thing that does not move. Good glazing keeps the heat in whatever the front of the certificate says, and with the launch date sliding about, the wait is better spent fixing the worst windows in the house than watching for an announcement.
Double Glazing Cost Calculator Team
What to do while the date is still moving
A slipping timetable is not a reason to sit on your hands, because the certificate is only the scoreboard. The heat still leaves through the same glass either way. The practical move is to improve the fabric first, and glazing is a large and visible part of that. You can put rough numbers on the running-cost side with our energy savings calculator, and if cost is the barrier it is worth checking what help is available through current double glazing grants before you commit. The main supplier-funded route is closing, as we explain in our coverage of the ECO4 extension to December 2026, and the wider funding picture traces back to the Warm Homes Plan.
The headline is simple enough. The certificate is being redesigned and the launch has moved, but the things that score well on it, warm fabric and good windows, have not changed at all.
Reformed EPC FAQs
For domestic EPCs the government will replace the existing single cost metric with four new headline metrics: energy cost, fabric performance, heating system and smart readiness. A secondary energy demand metric based on delivered energy and a secondary carbon-based metric sit behind them, and the legacy Energy Efficiency Rating is retained so new certificates can still be compared with current ones.
The launch was originally October 2026. In an update dated 9 March 2026, GOV.UK said it had decided to move the launch of the reforms to the second half of 2027, and that it would work with industry and the devolved administrations to agree a new launch date and shared implementation plan by the summer of 2026.
No published government source says that. The Home Energy Model was consulted on from January 2026, with the consultation closing on 18 March 2026, but no date has been confirmed for it becoming the required calculation method. The 1 October 2029 figure that circulates online is taken from a different rule entirely.
It is a transitional provision in the private rented sector Minimum Energy Efficiency Standards. Properties with a current EPC C are recognised as compliant under the future standard until that certificate expires, and that includes private rented homes graded C or above against the legacy Energy Efficiency Rating on EPCs issued before 1 October 2029. It is a cut-off for honouring older certificates, not a switch-on date for a new EPC engine.
The four headline metrics are published without a stated ranking, so no. Fabric-first ordering belongs to the private rented sector standard, which is a dual-metric standard with a fabric performance standard first, followed by landlord discretion to meet either a heating system standard or a smart readiness standard.
Yes. Windows count towards fabric performance under both the current EPC and the reformed one, and fabric performance becomes a headline metric in its own right rather than being folded into a single running-cost score. That makes glazing a durable improvement rather than a bet on one version of the rules.