When homeowners think about improving their Energy Performance Certificate (EPC) ratings, the focus often falls on heating systems, insulation, and lighting. However, one element is frequently underestimated: windows. While they may not appear as the most dramatic energy upgrade, their impact on a property’s efficiency rating is both measurable and often misunderstood.
Energy loss through windows accounts for up to 25% of a building’s heat inefficiency. And yet, many people assume that upgrading windows is prohibitively expensive or restricted by regulations—especially in period or leasehold properties. The result? Missed opportunities for affordable and accessible EPC improvements.
Your EPC score reflects the overall energy efficiency of a property. It’s based on several inputs, including the thermal performance of building materials, the heating system’s efficiency, and the property’s airtightness. Windows directly influence two of these factors:
EPC assessors examine whether your windows are single-, double-, or secondary-glazed. They also consider whether gaps around frames allow air infiltration. Old or poorly sealed windows often lose valuable points, especially in properties with high surface-to-volume window ratios like Victorian terraces or Georgian flats.
One of the most persistent myths in energy upgrades is the belief that double glazing is the only viable option. While modern double glazing is undoubtedly effective, it's not the only path to a higher EPC score—nor always the most practical.
Double glazing can be:
Many homeowners assume that without replacing their windows, there’s little they can do to improve efficiency. This is where secondary glazing proves invaluable: an underutilised and EPC-relevant upgrade.
A window’s U-value measures how well it prevents heat from escaping. The lower the U-value, the better the insulation. Here's a general breakdown:
While modern double glazing might achieve slightly lower U-values, the difference is not always EPC-defining—especially when weighed against planning challenges or costs.
What’s equally important is air infiltration. Even well-insulated windows can perform poorly if gaps allow uncontrolled draughts. Secondary glazing forms a sealed internal barrier that significantly enhances a property's airtightness—often enough to lift the EPC rating by a few crucial points.
Period homes—typically found in places like Edinburgh, Bath, and parts of London—pose a unique challenge for EPC upgrades. They often come with:
For these properties, replacing original windows is either not allowed or not desired. This doesn’t mean you're stuck with poor performance.
Secondary glazing, particularly high-quality systems like AirShield Glazing Panels, provide an internal solution that’s:
In many cases, it’s the only practical window-related upgrade that can be carried out without formal permission.
Let’s consider what a 3–6 point gain in EPC score actually means. For many properties currently rated in band D (scores between 55–68), a modest boost is all that’s needed to move into the C band (69–80).
An owner-occupied flat in a 1900s tenement had an EPC score of 61. Replacing the windows would’ve cost over £7,000 and required landlord consent. Instead, the owner installed AirShield Glazing Panels on six large sash windows.
A subsequent upgrade to LED lighting and radiator controls nudged the score to 70—comfortably in band C.
These kinds of sequential improvements show how small EPC gains from window upgrades create momentum for broader compliance.
AirShield Glazing Panels have been engineered to address the exact pain points facing homeowners with EPC goals:
For leaseholders, listed property owners, and landlords seeking to avoid major renovations, AirShield provides an EPC-friendly option that delivers results without compromise.
As of 2028, all rental properties in England and Wales will be expected to reach EPC band C. Scotland and Northern Ireland are expected to follow similar paths. The same applies to many mortgage lenders, green finance products, and future resale expectations.
Delaying upgrades only narrows your window for affordable compliance. Fortunately, you don’t need to replace your windows to act now.
By targeting your windows with strategic internal insulation like AirShield Glazing Panels, you can:
For thousands of homeowners, this is one of the simplest and smartest EPC moves they can make.
If your EPC score is hovering in the D range, your windows might be the low-hanging fruit you’re missing. Replacing them may not be necessary—or even permitted. But improving them with secondary glazing could make the difference.
AirShield Glazing Panels offer a precise, reversible solution that’s tailored to the types of windows most often found in period, urban, and listed properties.
Whether you're planning to sell, rent, or simply cut your energy bills, this might be the upgrade your EPC assessor—and your wallet—will thank you for.
