Britain’s older housing stock is one of the least thermally efficient in Europe, and windows are a major reason why. Millions of UK homes still contain glazing that was installed 20 or more years ago, quietly bleeding warmth into the outside air while adding unnecessary pounds to every energy bill. The problem is especially acute in terraced houses and semi-detached properties built before the 1990s, where single glazing or early double glazing may never have been replaced.
Windows losing heat at home can be identified by cold inner glass surfaces, condensation trapped between panes, draughts around frames, and persistently high heating bills. In a typical UK semi-detached home, inefficient windows account for up to 25 percent of total heat loss, costing households an estimated £95 to £130 more per year compared to A-rated double glazing. The most important step is to check whether your sealed units have failed — a tell-tale sign is cloudy or damp condensation between the panes — and then get quotes from FENSA-registered installers. Low-income households should check eligibility for ECO4 funding before committing to full replacement costs.
- Touch the inner glass surface on a cold morning — if it feels cold to the touch, your window is conducting heat out of your home and losing energy
- Condensation trapped between double-glazed panes means the sealed unit has failed and must be replaced, not just resealed
- Run your hand slowly around frame edges on a windy day to locate draught gaps before calling an installer
- Get 3 quotes from FENSA-registered or Certass-approved glazing installers to ensure work meets current UK building regulations
- Replacing single glazing with A-rated double glazing can save a typical semi-detached household between £95 and £130 per year on energy bills
- Check eligibility for the GB Insulation Scheme or ECO4 funding before paying full price — low-income households may qualify for subsidised or free glazing upgrades
- Book a professional window energy assessment if two or more heat-loss signs are present simultaneously, ideally before October so work can be completed ahead of winter
- Understanding Heat Loss Through Windows
- The Quick Answer — Signs Your Windows Are Losing Heat
- The Most Common Signs Your Windows Are Underperforming
- Simple Tests Any Homeowner Can Do at Home
- How Window Age and Type Affect Heat Loss at Home
- What Window Heat Loss Could Be Costing You in 2026
- Grants and Financial Support Available in 2026
- How to Choose the Right Fix for Your Windows
The most reliable signs that your windows are losing heat at home include cold glass to the touch on winter mornings, condensation forming between double-glazed panes, persistent draughts near the frame edges, and heating bills that remain stubbornly high despite no obvious change in habits. If two or more of these signs are present simultaneously, your windows are very likely contributing to significant heat loss and it is worth arranging a professional assessment before the next cold season begins.
Understanding Heat Loss Through Windows
Heat loss through windows occurs when warmth generated inside your home escapes outward through the glass and frame, forcing your heating system to work harder and longer to maintain a comfortable temperature. Understanding the basic physics behind this process helps explain why some windows fail far more dramatically than others, and why the difference between single glazing and modern high-performance glazing is far more significant than it might appear from the outside.
There are three main mechanisms by which windows allow heat to escape. Conduction is the transfer of heat directly through a solid material — in window terms, this means warmth passing straight through the glass pane and the frame itself into the cold outside air. Convection describes the way cold air adjacent to a poorly insulating window surface draws warmth downward and away from the room, creating cold draughts and cold spots on floors near windows. Radiation refers to the way infrared heat energy radiates outward through glass, particularly single glazing, which has almost no capacity to reflect radiated heat back into the room.
According to the Energy Saving Trust, windows and doors together can account for around 18 to 25 per cent of a home’s total heat loss. This makes glazing one of the most impactful areas any homeowner can address when looking to improve energy efficiency. To put that in context, losing a quarter of your home’s heat through its windows is roughly comparable to leaving a small window open continuously throughout the winter.
The difference in thermal performance between window types is substantial. Single glazing — still found in a significant number of older UK homes — consists of a single pane of glass with no insulating air gap, making it almost as thermally ineffective as a hole in the wall. Standard double glazing, widely installed from the 1980s onwards, introduced a sealed air gap between two panes, dramatically reducing conduction and convection losses. Modern A-rated double glazing and triple glazing, however, go considerably further: they use a wider gap filled with argon gas (a denser, less conductive gas than air), low-emissivity glass coatings that reflect radiated heat back into the room, and thermally broken frames that interrupt the conductive path between the cold outside and the warm inside. The result is a window that retains heat with an efficiency that older double glazing simply cannot match.
Practical tip — if you are unsure what type of glazing you have, look at the edge of the glass where it meets the frame. A single thin line of glass indicates single glazing. A visible gap between two panes indicates double glazing. You can also check for a small spacer bar at the edge of the unit, often silver or black in colour.
The Quick Answer — Signs Your Windows Are Losing Heat
The fastest way to know whether your windows are losing heat is to check for the four most common warning signs, all of which you can identify yourself without any tools or specialist knowledge.
- Cold glass to the touch — on a cold winter morning, energy-efficient modern glazing should feel only mildly cool; if it feels very cold or icy, heat is conducting straight through
- Condensation between the panes — fogging or droplets trapped inside a double-glazed unit mean the sealed unit has failed and is no longer insulating properly
- Draughts around the frame — cold air entering around the edges of the frame or through degraded seals is a clear indicator of air infiltration
- Unexplained increases in heating bills — if your usage habits have not changed but bills have risen, window heat loss may be a significant contributing factor
One of the most common challenges for homeowners is that these signs appear gradually over months and years. A sealed unit does not fail overnight; it slowly loses its insulating gas fill over time as the seal degrades. Similarly, rubber frame seals do not suddenly collapse — they compress, harden, and crack incrementally. This gradual deterioration means many households do not connect their windows to rising energy costs until the problem has become quite severe.
A straightforward at-home check requires nothing more than your hand and a cold day. Hold your open palm about five centimetres from the glass surface with the heating on — a noticeable chill at that distance indicates poor thermal performance. Running a slightly damp finger around the inner frame perimeter will reveal draughts as a cool sensation even on a relatively still day. These basic checks take less than five minutes per window and can give you a clear picture of where your home is losing heat.
If two or more of the warning signs described above are present in the same window, the window is almost certainly underperforming significantly. Arranging a professional assessment before the next heating season begins is a sensible and cost-effective step.
Practical tip — take photographs of any windows showing condensation between the panes and note the date. This documented evidence will be useful when discussing repair or replacement options with installers, and helps confirm whether the problem is persistent or weather-related.
The Most Common Signs Your Windows Are Underperforming
Knowing exactly what to look for makes it much easier to assess your home’s windows systematically. Each of the signs below points to a specific type of failure, which in turn helps determine the most appropriate and cost-effective remedy.
Cold Glass and Cold Spots Near Windows
On a winter morning with the heating running, modern energy-efficient double or triple glazing should feel only slightly cool to the touch — roughly comparable to touching a tiled worktop in a heated kitchen. If the glass feels genuinely cold, as though you are touching a surface exposed to the outside air, it is conducting heat directly out of the room at a significant rate. This is particularly common in homes with older double glazing that has lost its argon gas fill, or in homes where single glazing was never replaced.
Cold spots on walls and floors directly beneath windows are a secondary symptom of the same problem. Cold convective air rolling down the face of a cold window pane settles at floor level, creating draughty, uncomfortable zones that no amount of furniture arrangement can fully resolve. This convective effect is why rooms with large underperforming windows often feel cold even when the thermostat reads a comfortable temperature.
Condensation Between the Panes
This is one of the clearest and most unambiguous signs of window failure available to a homeowner. A sealed unit — the technical term for the double-glazed glass assembly — consists of two panes of glass separated by a spacer bar and hermetically sealed around the edges to trap an insulating gas (usually argon) in the cavity between them. When the seal fails, outside moisture enters the cavity and condenses on the inner surfaces of the glass, creating the characteristic foggy or streaky appearance that cannot be cleaned because it is trapped inside the unit.
Once a sealed unit has failed in this way, the insulating gas has been replaced by ordinary moist air, and the window’s thermal performance drops significantly — often approaching that of standard single glazing. The only effective remedy is to replace the sealed unit itself (which is possible without replacing the entire frame, provided the frame is still in good condition) or to replace the whole window.
Condensation on the Inside Surface of the Glass
It is important to distinguish condensation between the panes from condensation on the inner surface of the glass, which faces into the room. Internal surface condensation — droplets forming on the room-facing side of the glass — can indicate poor indoor ventilation, particularly in kitchens and bathrooms. However, when it appears consistently across multiple windows throughout the home, especially in combination with cold glass, it can also indicate that the glazing itself lacks sufficient thermal performance to keep its surface temperature above the dew point of the room air.
In practical terms, a window whose inner surface is cold enough to cause condensation is also cold enough to be losing significant heat. Improving ventilation alone will not resolve the underlying thermal deficiency.
Draughts Around Frames and Seals
The rubber or foam compression seals fitted around window frames serve a dual purpose — they prevent air infiltration and help weatherproof the frame against rain. Over time, these seals harden, compress permanently, and develop cracks that allow cold outside air to pass through into the room. Similarly, the external mastic sealant applied around the outside of the frame can shrink, crack, or detach from the wall surface, opening a channel for cold air to enter.
Homeowners can detect draught infiltration without any specialist equipment by holding a lit incense stick or a thin strip of tissue paper slowly around the entire frame perimeter on a cold and moderately windy day. Any movement in the smoke or tissue paper indicates a draught. Pay particular attention to the corners of the frame, the bottom edge, and any point where the frame meets the window sill, as these are the areas most prone to seal failure.
Practical tip — check your windows for draughts on a day with some wind, as light breezes will make small air leaks far more detectable than on a still day. Early morning in autumn or winter, before the heating has fully warmed the room, is the most revealing time for this test.
Simple Tests Any Homeowner Can Do at Home
The following tests require no tools, no trade knowledge, and no expense. Carried out methodically around your home, they will give you a reliable picture of which windows are underperforming and what type of problem each one has.
- The hand test for thermal performance — with the heating on and the outside temperature below ten degrees Celsius, hold your open palm approximately five centimetres from the glass surface. A noticeable chill at this distance indicates poor thermal performance of the glazing. Then move your hand to within a few centimetres of the frame edge and the seal line; a chill there, distinct from the glass surface, points to a draught or frame seal failure rather than a glazing issue.
- The tissue or candle test for draughts — hold a lit candle or a single sheet of thin tissue paper slowly around the entire frame perimeter, including the corners, the bottom edge, and along the window sill junction. Any flickering of the flame or movement of the tissue indicates air infiltration. This test is most effective on a cold, slightly windy day with the window closed fully.
- The condensation inspection — on a cold morning before the heating has been running for long, inspect every double-glazed unit in the home for fogging, droplets, or streaking between the panes. Failed units will show persistent fogging that does not clear as the day warms up, unlike temporary condensation on the outer surface caused by morning dew, which evaporates within an hour or two.
- The visual frame inspection from outside — walk around the exterior of your home and examine the mastic sealant where each window frame meets the surrounding masonry or render. Look for cracks, gaps, shrinkage, or sections where the sealant has pulled away from the wall surface. Also check for visibly warped or bowing frames, and look along the frame edge in low-angle light to see if any daylight is visible from a crack or gap.
- The heating bill comparison — compare your energy consumption (in kilowatt hours, shown on your bill) for the same winter months over the last two or three years, adjusting mentally for any changes in usage habits or household size. A sustained upward trend in consumption without a clear alternative explanation is consistent with degrading window performance, among other causes.
Practical tip — carry out these tests on all windows in the home, not just the ones you already suspect. It is very common to find that a window in a less-used room, such as a spare bedroom, has failed more severely than the main living room windows that receive more regular attention.
How Window Age and Type Affect Heat Loss at Home
The age and specification of your windows are two of the most reliable predictors of current thermal performance, and understanding both helps homeowners prioritise which windows to address first.
The typical lifespan of a double-glazed sealed unit is around 20 to 25 years, though this varies depending on installation quality, frame condition, and exposure to driving rain and direct sun. Windows installed during the 1990s and early 2000s — which describes the glazing in a very large proportion of UK homes — are now at or beyond this threshold. Even if they appear visually intact, the seals may have degraded sufficiently to allow gas escape and moisture ingress, silently reducing their thermal performance year on year.
The key measurement of a window’s thermal performance is its U-value, which measures the rate of heat transfer through a material in watts per square metre per degree of temperature difference (W/m²K). A lower U-value means less heat escapes — it is better for energy efficiency. To give a practical sense of the range involved, single glazing typically has a U-value of around 5.0 W/m²K, older double glazing sits at around 2.8 to 3.0 W/m²K, and modern A-rated double or triple glazing achieves 1.4 W/m²K or below for the whole window unit including the frame. In everyday terms, this means modern glazing can lose less than a third of the heat that older double glazing loses through the same area of glass.
Frame material also plays a significant role. uPVC frames are generally good thermal insulators and are the most common frame type in UK replacement window installations. Timber frames, if well maintained and draught-sealed, also perform reasonably well thermally. Aluminium frames, however, are highly conductive metals, and older aluminium-framed windows without a thermal break — a section of insulating material separating the inner and outer parts of the metal frame — are a well-known source of cold spots, surface condensation, and significant heat loss. Many aluminium-framed windows fitted before the late 1990s lack thermal breaks entirely.
For homeowners comparing replacement window products, the BFRC Window Energy Rating scheme — run by the British Fenestration Rating Council — provides a straightforward A-to-G label similar to those used on household appliances. An A-rated window delivers the best combination of low heat loss and, where relevant, useful solar heat gain. This label allows a straightforward product comparison without needing to interpret U-value data directly.
| Window Type | Typical U-value (W/m²K) | BFRC Rating (approximate) | Relative Heat Loss |
|---|---|---|---|
| Single glazing | Around 5.0 | Not applicable | Very high |
| Older double glazing (1990s) | 2.8 to 3.0 | E to G | High |
| Standard double glazing (2000s) | 2.0 to 2.8 | C to E | Moderate |
| Modern A-rated double glazing | 1.4 to 1.6 | A to B | Low |
| Triple glazing | 0.8 to 1.2 | A or above | Very low |
Practical tip — if your home has aluminium-framed windows fitted before the year 2000, have them assessed as a priority. The absence of a thermal break in these frames makes them disproportionately poor performers compared with their uPVC contemporaries of the same age.
What Window Heat Loss Could Be Costing You in 2026
Understanding the financial impact of underperforming windows requires connecting the physics of heat loss to the real cost of energy in the current market. In 2026, under Ofgem‘s energy price cap framework, UK households pay a regulated unit rate for gas and electricity, meaning that every unit of heat that escapes through a poorly insulated window has a direct and calculable cost attached to it. When a window loses heat, your boiler runs longer to compensate — and every additional hour of boiler operation adds to your bill.
According to Energy Saving Trust guidance, upgrading from single glazing to A-rated double glazing in a typical semi-detached home can generate meaningful annual savings, though the exact figure varies considerably based on home size, the number of windows replaced, the heating fuel used, and the current energy tariff. The Energy Saving Trust provides a personalised savings calculator on its website that uses your home’s details to give a more accurate estimate than any generic figure could. guide to EPC ratings and what they mean for your energy bills
The cost of different remedial options varies widely, and it is important to distinguish between a straightforward seal repair, a sealed unit replacement, and a full window replacement — as the cost and disruption involved are very different.
| Remedy | What it addresses | Approximate 2026 Cost (per window) | Typical Disruption |
|---|---|---|---|
| Resealing frame with mastic | Draughts from external frame gaps | £50 to £150 as a DIY or trade job | Minimal — a few hours |
| Replacing rubber compression seals | Draught infiltration around the opening sash | £80 to £200 per window (trade) | Half a day per room |
| Replacing failed sealed unit only | Condensation between panes, loss of argon fill | £150 to £400 per unit depending on size | One to two hours per window |
| Full window replacement (double glazed) | Failed frames, poor U-values, multiple issues | £600 to £1,500 per window (standard size) | One day for a typical house |
| Upgrade to triple glazing | Maximum thermal performance improvement | £900 to £2,000 per window (standard size) | One to two days for a typical house |
Beyond the direct energy cost, there is a compounding financial case for addressing window heat loss promptly. Poorly performing windows contribute to elevated indoor humidity levels, increasing the risk of damp and mould — both of which carry their own remediation costs and health implications. They also affect a home’s Energy Performance Certificate (EPC) rating, which from 2026 onwards carries increasing relevance for mortgage lenders and prospective buyers. A home with a poor EPC rating may face restrictions on lettings and could attract a lower sale price. how to improve your home's EPC rating before selling
Practical tip — before committing to full window replacement, ask an installer to assess whether the frames are still structurally sound and thermally acceptable. If the frames are in good condition and the only problem is a failed sealed unit, replacing the glazing unit alone is significantly cheaper and produces broadly similar thermal results.
Grants and Financial Support Available in 2026
Several UK government schemes may be able to help homeowners fund window improvements in 2026, though eligibility criteria vary and windows are not always covered as a standalone measure — they are more commonly funded as part of a broader energy efficiency package.
ECO4
ECO4 — the Energy Company Obligation scheme in its fourth phase — requires larger UK energy suppliers to fund energy efficiency upgrades for low-income and vulnerable households. Window improvements can be included under ECO4 as part of a whole-house retrofit package, provided the home and householder meet the relevant eligibility criteria, which are assessed on the basis of income, benefit status, and the home’s current energy efficiency level. Homeowners who believe they may qualify should contact their energy supplier directly or use the Simple Energy Advice service (managed by the Energy Saving Trust on behalf of the government) to carry out an eligibility check. ECO4 is not a grant that homeowners apply for independently — it is delivered through an installer network coordinated by energy suppliers.
Great British Insulation Scheme
The Great British Insulation Scheme (GBIS) is a separate government programme focused primarily on insulation measures for poorly insulated homes. While windows are not its primary focus, glazing improvements may be included where they form part of a broader retrofit plan for eligible properties. Eligibility under GBIS is based on a combination of the home’s current EPC rating and council tax band. Given that the scheme’s scope and available funding are subject to periodic government review, homeowners should check current guidance from the Department for Energy Security and Net Zero (DESNZ) before making plans on the basis of GBIS support. full guide to the Great British Insulation Scheme eligibility and how to apply
Boiler Upgrade Scheme — an indirect connection
The Boiler Upgrade Scheme (BUS) provides £7,500 towards the installation of an air source heat pump, and a higher figure towards ground source heat pump installations. While BUS does not directly fund window improvements, there is an important indirect connection worth understanding. Heat pumps operate most efficiently in well-insulated homes with low overall heat demand. Upgrading windows before installing a heat pump reduces the home’s heat loss, which in turn means the heat pump can be specified at a smaller, cheaper capacity and will run more efficiently throughout its life. For any homeowner considering a heat pump installation under BUS, addressing significant window heat loss in advance is widely recommended by installers and is consistent with the whole-house approach that underpins the scheme. is a heat pump right for my home — what you need to know before applying for the Boiler Upgrade Scheme
Local Authority and Regional Schemes
Beyond the national schemes, many local authorities operate their own retrofit programmes, sometimes using funding from the Warm Homes Local Grant or other regional sources. These schemes vary considerably in scope, eligibility, and the measures they cover, and some specifically include window upgrades for hard-to-treat homes. It is worth contacting your local council’s housing or energy team directly to ask what is currently available in your area.
Before applying for any grant or scheme, obtaining an up-to-date EPC for your home is strongly advisable. The EPC rating sits at the centre of most eligibility assessments, and without a current certificate, many applications cannot proceed. EPCs are valid for ten years, but if yours is more than five or six years old and you have made improvements since it was carried out, commissioning a new assessment may reveal a higher rating that affects your eligibility for certain support.
Practical tip — always check current eligibility criteria directly with the administering body before making decisions based on grant support. Scheme rules, funding levels, and qualifying criteria can change between government spending reviews, and the specific figures and conditions applicable at the time of your application are the ones that matter.
How to Choose the Right Fix for Your Windows
Not every underperforming window needs to be fully replaced, and not every draught requires a new sealed unit. Matching the right remedy to the specific problem identified saves money, avoids unnecessary disruption, and delivers the most efficient improvement possible. Follow these steps to work through the decision logically.
- Identify the specific problem in each window — use the tests described earlier in this article to categorise what is wrong. Condensation between the panes points to a failed sealed unit. Draughts detected at the frame edge but not through the glass point to failed seals or degraded mastic. Cold glass with no draught but poor thermal performance points to glazing that has a high U-value and may benefit from a unit upgrade or full replacement. Each problem has a different remedy, and misidentifying the cause leads to spending money on the wrong fix.
- Get a professional assessment before committing to any expenditure — contact a FENSA-registered or CERTASS-registered installer for a survey. FENSA and CERTASS are the two government-authorised bodies in England and Wales that certify window and door installations for compliance with Building Regulations — using a registered installer means the work is self-certified and does not require a separate building control application. Ask the installer to check the U-values of any proposed replacement glazing against current Building Regulations Part L standards, which require replacement windows to achieve 1.4 W/m²K or better for the whole unit. Always verify registration status on the FENSA or CERTASS online registers before booking any work.
- Decide whether to repair or replace the whole window — if the frame is structurally sound, thermally competent, and cosmetically acceptable, replacing only the failed sealed unit is a cost-effective approach that avoids the labour and material cost of a full window replacement. If the frame itself is warped, has lost its thermal integrity, or is an older aluminium frame without a thermal break, full replacement is likely to deliver better long-term value despite the higher upfront cost.
- Consider upgrading rather than like-for-like replacement — if a window is being replaced anyway, the additional cost of specifying A-rated glazing or triple glazing over a standard replacement is often modest relative to the total job cost, while the long-term thermal and financial benefit is considerably greater. Ask your installer to quote for both options so you can compare the difference in cost against the improvement in U-value.
- Address draughtproofing as a low-cost immediate measure — where budget constraints make full replacement or unit replacement impractical in the short term, professional draughtproofing of frame seals and external mastic is a low-cost interim measure that can meaningfully reduce heat loss and improve comfort. Draughtproofing means sealing the gaps and cracks around windows through which cold air infiltrates, typically using replacement rubber compression seals, brush seals for sash windows, and fresh external mastic around the frame perimeter. This will not address failed sealed units or genuinely poor glazing U-values, but it can reduce the draught-related component of heat loss significantly.
- Ensure all work is carried out by an appropriately registered installer — for window replacement, FENSA or CERTASS registration is the relevant accreditation to look for in England and Wales. For any electrical work associated with integral blinds or smart glazing, the installer should be registered with NICEIC or NAPIT — both are government-approved bodies for electrical work in homes. For any work carried out as part of a grant-funded scheme, check that the installer is registered with TrustMark, which is the government-endorsed quality scheme for retrofit and home improvement work. You can verify all of these accreditations on the respective official registers before agreeing to any work.
Getting at least three quotes from different FENSA or CERTASS-registered installers is strongly recommended before committing to any significant window work. Prices for the same specification can vary considerably between companies, and a written specification from each installer allows meaningful like-for-like comparison. Be cautious of quotes that seem significantly lower than others without a clear explanation, and ask each installer to confirm in writing which U-value their proposed glazing achieves, what energy rating it carries under the BFRC scheme, and what the installation guarantee covers and for how long. what to look for in a window replacement quote — a homeowner's checklist
Practical tip — if you are in a conservation area or your home is listed, you will need to check with your local planning authority before replacing windows, as there may be restrictions on the type or appearance of glazing permitted. Some conservation areas now allow slim-profile double glazing that closely resembles traditional single-glazed windows, so options do exist even in constrained circumstances.
Frequently Asked Questions
how can I tell if my double glazing is letting heat out?
The clearest signs are condensation forming between the two panes (indicating a failed seal), cold glass on the inside surface during winter, and persistent draughts near the frame. A failed sealed unit loses its insulating argon or krypton gas fill, reducing thermal performance to near single-glazing levels. A professional glazier can assess units from around £50 to £80 for a survey.
how much heat is lost through windows in a typical UK home?
Windows account for roughly 18 to 25 percent of total heat loss in a typical UK home, according to the Energy Saving Trust. Homes with single glazing lose significantly more than those with modern double or triple glazing. Upgrading from single to A-rated double glazing can cut window-related heat loss by up to 50 percent.
how much does it cost to replace double glazing in the UK?
Replacing a failed double-glazed sealed unit typically costs between £70 and £200 per pane depending on size, while a full window replacement ranges from £400 to £900 per window for standard uPVC frames. A full house replacement for a 3-bedroom semi-detached property usually costs between £4,000 and £7,500 in total. Always get quotes from FENSA-registered installers to ensure compliance with UK building regulations.
can I get a grant to replace my windows in the UK?
Low-income or vulnerable households may be eligible for support through the ECO4 scheme, which can cover partial or full glazing replacement costs when bundled with other energy efficiency measures. The GB Insulation Scheme also covers some window upgrades for qualifying properties. To check eligibility, contact your energy supplier directly or use the government's simple energy advice service.
is it worth upgrading to triple glazing in the UK?
Triple glazing offers better thermal performance than standard double glazing, with U-values typically between 0.6 and 0.8 W/m²K compared to around 1.2 to 1.6 W/m²K for double glazing. However, the additional cost of around 20 to 30 percent over double glazing means payback periods can be long in most UK climates. Triple glazing is most cost-effective in exposed northern locations, older properties with single glazing, or new builds targeting high energy performance standards.
