How New Windows Improve Your EPC Rating: 2026 Update

Energy Performance Certificates are changing, just later than planned. The reformed EPC will add a standalone Fabric Performance score that measures how well your building envelope (walls, roof, floors and windows) retains heat, separately from the overall rating. In March 2026 the government confirmed that this reform will now land in the second half of 2027 rather than October 2026. For homeowners, the new score will be useful information. For landlords, the compliance deadline that matters has not moved at all.

What Is Changing, and When

Today, EPCs assess your property on a scale from A (most efficient) to G (least efficient), based on a combination of heating system, insulation, hot water, lighting and glazing. That is the certificate you will still get if you order one this year. From the second half of 2027 the reformed certificate is expected to keep an overall rating but add separate metrics, including Fabric Performance, so a property with an efficient boiler and LED lighting could still score poorly on fabric if its windows are old and inefficient. The intention is to drive investment in the physical fabric of buildings, not just quick fixes.

The Landlord Deadline: EPC C by 1 October 2030

Private rented homes in England and Wales must reach an EPC rating of at least band C by 1 October 2030 for all tenancies. Where that is not possible, landlords will need to show they have spent up to the cost cap, now set at £10,000 per property (or 10% of the property's value where it is worth less than £100,000), on eligible improvements. The earlier proposals for a 2028 date for new tenancies and a £15,000 cap were dropped. For landlords with properties in bands D, E or lower, the sensible time to act is now, not in 2029 when every installer in the country will be overloaded with compliance work.

How Much Do Windows Improve Your EPC?

Windows are one of the highest-impact upgrades you can make to your EPC rating. The exact improvement depends on your property type, current glazing, and overall condition, but here are the typical ranges we see across our Bristol, Exeter, and Cardiff installations:

• Replacing single glazing with A++ double glazing: 15-28 point improvement.
• Upgrading pre-2002 double glazing (old sealed units with no low-e coating): 8-18 point improvement.
• Upgrading post-2002 double glazing to A++ rated units: 5-10 point improvement.
• Moving from double to triple glazing: an additional 3-8 points on top of the above.

To put this in context, the difference between EPC band D (55-68 points) and EPC band C (69-80 points) is often just 10-15 points. A full set of replacement windows frequently bridges exactly that gap, making windows the single most effective upgrade for landlords hovering around the D/C boundary. Our free EPC calculator gives you an estimate for your own property.

What About the Fabric Performance Metric?

When it arrives, the Fabric Performance score is expected to weight glazing heavily because windows are typically the weakest part of any building envelope. A single-glazed window has a U-value of approximately 5.0 W/m²K. A modern A++ double-glazed unit achieves around 1.0-1.2 W/m²K. Triple glazing reaches 0.8 W/m²K. That is a 75-85% reduction in heat loss through the glass alone, before accounting for improved frame insulation and draught sealing. Windows fitted now will count under both the current certificate and the reformed one.

The Investment Case for Landlords

A typical 3-bedroom rental property with 8 windows can be upgraded to A++ double glazing for £3,500-5,500, comfortably inside the £10,000 cap. The return on investment comes from three sources: continued ability to legally let the property (avoiding void periods), energy bill savings passed through to tenants (making the property more attractive in a competitive rental market), and increased property value. EPC improvements have been shown to add 5-10% to sale prices in recent studies.

We offer landlord-specific packages with volume pricing for portfolio owners. If you have multiple properties, talk to us about a phased upgrade programme.