A standard uPVC casement window, supplied and fitted, typically costs £350–£700 in 2026. A full re-glaze of an ordinary 8–10-window semi runs to roughly £4,000–£10,000 in uPVC, more for aluminium, and roughly double again for timber — which is often the only frame a conservation officer will approve. Sash and bay windows cost considerably more than a plain casement, and if the house is listed, the whole conversation usually needs to shift from "double glazing" to "secondary glazing" before it goes anywhere.
But the figure worth pausing on before the quote isn't really the price, it's what you're buying with it: heat retained, noise excluded, an EPC rating nudged up, or just a tidier-looking elevation. For genuinely old, ill-fitting single glazing, the case for replacement is usually clear-cut. For a house that already has reasonable double glazing from the 2000s onward, the return on ripping it out and starting again is a lot less obvious than a sales visit tends to suggest.
I assess and rate buildings for a living, EPCs included, and I don't sell or fit windows, so I've no stake in whether you go ahead. What follows is the pricing, plus the questions I'd actually want answered before signing anything.
The short answer
Figures below were checked on 31 July 2026 against Checkatrade, MyBuilder, MyJobQuote and doubleglazingcostcalculator.co.uk's 2026 cost guides. As with most trades in this series, Kent, Sussex, Surrey and London trend above the national averages quoted here.
| Window / job | Typical cost (2026) | What's included |
|---|---|---|
| uPVC casement, standard size (per window) | £350–£700 | Supply, fit, removal of old frame, FENSA certificate |
| uPVC sash or bay window (per window) | £700–£2,500 | Slimline sightlines or multi-panel bay, more labour |
| Whole house, 3-bed semi, uPVC (8–10 windows) | £4,000–£10,000 | As above, with per-window economies of scale |
| Whole house, same size, timber or aluminium | £8,000–£16,000+ | Heavier frames, often specified in conservation areas |
Checkatrade's own published range for a casement window runs higher still, at roughly £500–£1,250, which reflects larger and higher-spec windows rather than a standard opening. Treat any single figure quoted to you with that spread in mind, get the exact size and glazing spec confirmed in writing, and compare two quotes on that basis rather than the headline number alone.
What drives the price
Frame material. uPVC is the default and the cheapest option. Aluminium slim-frame windows typically cost around 50% more. Timber costs roughly double uPVC, and is often the only material a conservation officer will approve on a period property.
Window style. A standard casement opener is the baseline figure. Sash windows run to roughly double a casement's price because of the weighted mechanism and slimmer sightlines involved; bay and bow windows can cost up to twice a casement per opening once the extra panels and structural support are factored in; tilt-and-turn sits a modest step above casement.
Glazing spec. Beyond "double glazed" as a label, Low-E coatings, argon gas fill and warm-edge spacer bars all improve the actual U-value for a modest extra cost, and they're worth asking for by name rather than trusting "energy efficient" on a brochure to mean anything specific.
Access and structural work. Upper-floor windows, bay windows needing a new lintel or additional support, and old sash boxes needing repair before a new sash goes in all add labour well beyond the cost of the glass itself.
FENSA and Building Regulations compliance. A reputable installer prices this in as standard. It shouldn't appear as a separate line on the quote, and a quote that doesn't mention it at all is worth querying before you sign.
Region. Kent, Sussex, Surrey and London trend above the national figures quoted here, in line with most trades in this series.
Do you actually need it — and does it move your EPC rating?
The single biggest factor in whether replacement windows are worth it isn't the window, it's what's there already. Swapping out genuinely old single glazing, or early double glazing with failed seals and thin aluminium spacer bars, for a modern A-rated unit is where the real gains sit — typically 8–18 EPC points, sometimes enough to shift a property a full band on its own. Swap out double glazing that's already reasonably modern, though, and the numbers get far less generous: 2–5 points is the more realistic outcome, because the RdSAP methodology behind every EPC applies a fairly coarse set of window categories rather than crediting every incremental improvement.
The point that genuinely catches people out is going from double to triple. Under the standard software, double and triple glazing are frequently assigned the same default U-value band in a uPVC frame, so a full triple-glazing upgrade can do precisely nothing to your certificate, even though it might honestly improve comfort and noise inside the room. If an EPC rating is the reason you're replacing windows, it's worth having someone check what your assessment would actually show before committing to the spend, rather than assuming glazing is the lever that moves it. I carry out EPCs as part of my own practice, and windows are consistently one of the more oversold measures against the points they actually deliver, next to loft insulation or proper draught-proofing done first.
Beyond the EPC arithmetic, condition is the other honest test. Draughts, misting between the panes — a failed seal, not a symptom of the whole frame failing — and hinges or handles that won't lock are all worth checking before assuming a full replacement is the only fix. A misted double-glazed unit can often be swapped on its own for roughly £225–£275 per pane, a fraction of a new window, and it's a five-minute job for anyone who knows what they're looking at.
Conservation areas, listed buildings and grants
If the house is listed, park the idea of a standard uPVC replacement — it's very likely to be refused, on any grade of listing, because the windows are typically as much a part of what's protected as the walls around them. In a conservation area that isn't listed, replacing original windows on an elevation facing a road with uPVC usually needs planning permission too, and is often turned down; windows away from the street generally have more latitude, though an Article 4 direction can remove even that.
Secondary glazing — a second, internal pane fitted inside the existing window, leaving the original completely untouched — is the route conservation officers actually favour, because it's reversible and because the wider air gap it creates often outperforms a sealed double-glazed unit on noise. It usually doesn't need planning permission on conservation-area grounds, though on a listed building you technically need listed building consent for it too. In practice, most conservation officers will approve a well-detailed secondary glazing scheme without much friction, but it's worth checking with them before you order rather than after.
On grants: the Warm Homes: Local Grant is the current scheme that explicitly covers glazing, worth up to £15,000 towards fabric measures — insulation, doors and windows together — for households on a property rated EPC D–G with income under £36,000, delivered through your local council. It's a fabric-first scheme, so an assessor is likely to fund insulation ahead of glazing if your loft or cavity walls need attention first; windows aren't usually funded on their own. Eligibility is means-tested and postcode-dependent, so most homeowners paying market rate for a replacement won't qualify — check with your local authority or gov.uk before assuming either way.
What I'd watch for in a quote
- A FENSA certificate confirmed in writing, or a clear explanation of how building control sign-off is being handled if the installer isn't FENSA-registered.
- The Window Energy Rating or U-value stated, not just the word "double glazed" — a poorly specified double-glazed unit can perform worse than a well-specified one with the same glazing count.
- An itemised breakdown: frame material, glazing spec, ironmongery, disposal of the old units, and making good to the reveals.
- An insurance-backed guarantee that survives the installer going out of business.
- Scepticism of any "EPC points" claim for a double-to-triple upgrade specifically — ask what it would actually do to your certificate, not what it should do in theory.
- No pressure to sign on the day. A genuine quote doesn't expire at midnight.
Questions I get asked
Will new double glazing actually improve my EPC rating? Depends on what's there now. Replacing single glazing typically adds 8–18 points, sometimes a full band. Replacing already-reasonable double glazing usually adds only 2–5, and double-to-triple upgrades often add nothing at all under the standard methodology, since the software applies the same default U-value band to both in a uPVC frame.
Do I need planning permission to replace windows? Most replacements are permitted development. Two real exceptions: listed buildings, where standard double glazing is usually refused outright, and conservation areas, where street-facing replacements often need permission. Windows away from the road generally have more latitude.
Is triple glazing worth the extra cost? It typically adds 15–30% to the price. Worthwhile if the home is cold, exposed or noisy, or you're upgrading from single glazing and want the best available result; a weaker case if you're already on reasonable double glazing, where the extra rarely earns itself back before the windows need replacing again.
How do I know new windows meet Building Regulations? A FENSA certificate is the standard proof, issued automatically by a FENSA-registered installer and needed by your solicitor if you ever sell. Without FENSA, the installer needs separate building control sign-off — worth confirming which route they're using before work starts.
Whether new windows are worth it, and what they'd actually do to a certificate or a heating bill, is easier to answer from outside the sale than inside it. An EPC assessment tells you exactly what your current windows are costing you in rating terms, and where the money's better spent if it isn't glazing at all; a retrofit assessment looks at the whole fabric package if you're weighing several measures at once. Call 07946 618203 or get in touch and I'll give you a straight read before you commit.
Small print. This guide is general information, not advice on a specific property, and it doesn’t replace a written quote and a proper condition check of your own windows. Prices were researched and correct to the best of my knowledge on 31 July 2026; costs, grant rules and planning policy move and vary by region, property and council. Always get at least three written quotes, and confirm FENSA registration before signing anything.