Energy Performance Certificates (EPCs) are a critical component of the UK’s drive toward energy efficiency and net-zero targets. Issued whenever a property is built, sold, or rented, EPCs assess a building’s energy use and recommend ways to reduce carbon output and cut fuel bills. Ratings range from A (most efficient) to G (least efficient), and since 2020, properties let in the private rental sector must meet a minimum standard of E.
But that bar is rising. By 2028, all new and existing tenancies in England and Wales will be required to meet EPC band C. For property owners—especially landlords—this creates urgency. A poor EPC could affect not only a building’s legal viability but also its value, marketability, and rental appeal.
Among all building elements assessed in the EPC, windows stand out. Glazing contributes heavily to heat loss, and any thermal inefficiency directly drags down a property’s score. Poorly insulated windows are often the single largest source of unwanted heat transfer, meaning even modest upgrades can produce measurable results.
Replacing windows with modern double glazing might seem like an obvious fix—but it's often not possible. Many UK homes, particularly those in conservation areas or built before the mid-20th century, still retain original timber-framed sash or casement windows.
In these buildings, heritage considerations limit what owners can do. Double glazing typically requires new frames, which alter the façade and can clash with architectural guidelines. Even when technically allowed, replacements are expensive, intrusive, and irreversible. For leaseholders, shared freehold residents, or listed building owners, securing approval can be nearly impossible.
Even outside designated heritage zones, full replacement may be cost-prohibitive or simply overkill. If you're already improving wall insulation or updating your boiler, replacing windows could be the most expensive intervention with the least gain per pound spent.
This has led a growing number of property owners to look for smarter internal-only improvements—ones that boost performance, require no planning permission, and preserve the building’s aesthetic and character.
Secondary glazing is an internal solution that adds a second transparent panel to the inside of an existing window. This creates an air gap—an insulating barrier that significantly reduces heat loss. And from an EPC perspective, that matters.
The EPC rating system uses a metric called the U-value to measure how much heat passes through a material. The lower the U-value, the better the insulation. Here’s a quick reference:
Secondary glazing typically halves the U-value of a single-glazed window. While it may not reach the absolute efficiency of new double-glazing, the improvement is substantial—and more than enough to make a difference in your EPC score.
EPCs also consider air leakage and draughts. Many traditional windows, especially sash types, allow cold air to infiltrate. Secondary glazing forms a sealed air pocket that stops those draughts, improving the airtightness score of the building envelope.
Combined, these benefits help reduce a property’s overall heating demand, which directly influences the energy cost per square metre—a key calculation behind the EPC letter grade.
The owner of a 1930s sandstone flat in central Edinburgh faced high winter heating bills and a middling EPC of 64 (band D). The building’s conservation status prevented external window changes, but five large sash windows were retrofitted with internal secondary glazing panels.
After the upgrade, the EPC re-assessment recorded a new score of 69—pushing the property into band C. This qualified the flat for more favourable rental rates and helped meet the landlord’s 2028 compliance obligations.
Another example comes from a three-bedroom terraced house in Brighton. With ornate bay windows and original timber sashes, replacing the front windows would have disrupted the heritage façade. The homeowner opted for non-invasive secondary glazing option instead.
Result: The EPC improved from 62 (D) to 70 (C). According to the report, glazing improvements contributed a major share of this jump, alongside loft insulation.
A modern leasehold flat with large but leaky single-pane glazing faced EPC concerns due to high heat loss through windows. The lease terms prohibited any change to the exterior, but the owner installed AirShield Glazing Panels internally. The slim, unobtrusive design preserved the modern aesthetic while improving performance.
The EPC rating rose from 67 (D) to 71 (C), enough to satisfy future rental criteria without undertaking more disruptive work.
Across these examples, the gain in EPC points from secondary glazing typically ranges from 3 to 6 points. That may be all it takes to lift a property from D to C, particularly if other upgrades have already been made.
AirShield Glazing Panels are specifically designed for properties where standard window replacement isn’t an option—or where owners simply want a more efficient and elegant solution.
These panels are cut to fit your window openings exactly, with a push-fit frame that requires no drilling, adhesives, or tools. This makes them ideal for:
Because AirShield Glazing Panels improve energy performance without structural change, they are uniquely suited for unlocking EPC gains in harder-to-upgrade homes.
As the 2028 EPC legislation looms, homeowners and landlords alike are looking for practical, cost-effective ways to reach compliance—especially where traditional upgrades hit regulatory or financial walls.
Secondary glazing stands out as a quiet workhorse: unobtrusive, effective, and quick to implement. Whether you're dealing with conservation rules, budget limits, or time pressure, it could be the missing link in your EPC upgrade plan—especially when using smart, non-invasive options like AirShield Glazing Panels that blend seamlessly into existing window setups while delivering measurable performance gains.
