How New Windows Improve Your EPC Rating in 2026

Energy Performance Certificates are changing. This October, the UK government is introducing a new standalone Fabric Performance metric that specifically measures how well your building envelope (walls, roof, floors, and windows) retains heat. This is separate from your overall EPC rating and will appear as its own score on the certificate. For homeowners, this is useful information. For landlords, it is a compliance requirement that carries real financial consequences.

What Is Changing in October 2026?

Currently, EPCs assess your property on a scale from A (most efficient) to G (least efficient), based on a combination of factors including heating system, insulation, hot water, lighting, and glazing. The new system retains this overall rating but adds a Fabric Performance metric that isolates the building envelope. This means a property could have an efficient boiler and LED lighting but still score poorly on Fabric Performance if the windows are old and inefficient. The government's intention is to drive investment in the physical fabric of buildings, not just quick fixes like smart thermostats.

The Landlord EPC C Deadline: 2030

Private rental properties in England and Wales must achieve an EPC rating of at least band C by 2030. Properties that fail to meet this standard will be unlettable: landlords will not be able to legally grant new tenancies or renew existing ones. The current exemption cap of £3,500 is expected to remain, but the government has signalled that enforcement will be significantly tighter than the current EPC E minimum. For landlords with properties in bands D, E, or lower, action is needed 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: 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.

What About the Fabric Performance Metric?

The new Fabric Performance score will 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 draft sealing. For the Fabric Performance metric, this is transformational.

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. 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.