Replacement is a different purchase from repair. A repair puts a new part into a window you keep; a replacement takes the whole unit out of an existing opening and puts a new one in, which makes it notifiable work with a legal performance floor attached to it. This page covers what that job costs, what the fitted price buys you, what the new windows have to achieve, and how to scope it before you take quotes.
When a window needs replacing rather than repairing
The short version: the frame decides. If the uPVC frame is square, dry and still sealing, a failed sealed unit is a £55 to £145 repair and replacement is money wasted. If the frame is warping, cracking or no longer sealing, a new sealed unit cannot seat properly in it and replacement is the only durable answer. Sealed units last 15 to 20 years and uPVC frames 20 to 25, so a house at the 20-year mark with several blown units is usually past the point where repairs pay. We have set that decision out in full, with both sets of prices, on our repair versus replace comparison, and you can price the repair side on the repair cost calculator or identify the fault first with the window fault checker. The rest of this page assumes you have already landed on replacement.
What you are replacing decides what the job is worth
This is the question most replacement quotes never ask, and it changes the value of the job more than any specification choice. The saving comes from the gap between the old window and the new one, not from the new one on its own.
| What is being replaced | U-value | Gap to a modern A-rated unit |
|---|---|---|
| Single glazing | ~4.8–5.8 W/m²K | Very large |
| Old double glazing, pre-2002 | ~2.8–3.2 W/m²K | Roughly half as large |
| Modern A-rated double glazing | 1.0–1.4 W/m²K | None, this is the target |
| Triple glazing | 0.6–1.0 W/m²K | Already beyond it |
Source: DGCC 2026 dataset. U-value is heat lost per square metre per degree of temperature difference, so lower is better.
The Energy Saving Trust puts the saving from A-rated double glazing at £85 a year for a typical semi in Great Britain and £140 a year in Northern Ireland, and both figures are measured against single glazing. If your existing windows are already double glazed and simply old, you are starting from about 2.8 to 3.2 W/m²K rather than 4.8 to 5.8, so the energy return on the job is considerably smaller than those headline numbers and no honest quote should promise them to you. Our energy savings calculator models the single-glazing case, and the guide to U-values explains what the figures in that table mean.
That does not make a second-generation replacement a bad decision. It moves the case onto the reasons that actually apply: a frame at the end of its 20 to 25 year life, repeated sealed unit failures across the house, draughts, noise, security, hardware that no longer locks, or an EPC that has to move. It just means the payback arithmetic on whether double glazing is worth it looks different for you than for a homeowner still on single glazing.
What a fitted replacement price includes
The window is the smaller half of what you are buying. A basic uPVC casement costs from around £160 supply-only, and fitting labour runs roughly £300 to £600 per window, which is why the same window arrives at £400 to £1,000 fitted. The gap between the two routes is £200 to £600 per window, and our supply-only versus fully fitted comparison weighs whether it is worth taking on.
On a fully fitted replacement, that labour figure should cover the technical survey and exact measurement, removing the old window, taking the old frames away and disposing of them (never a separate charge on a fitted price), levelling and fitting the new frame, sealing it inside and out, fitting trickle vents and hardware, and registering the work so your FENSA or CERTASS certificate follows in the post.
Making good is the line to watch. Taking a window out of an existing opening disturbs the plaster on the internal reveal and sometimes the render or pointing outside. Whether the installer makes that good, or leaves you with a decorator's job, is the single most common difference between two replacement quotes that otherwise look identical. Ask for it explicitly and get the answer in writing.
What replacement windows must legally achieve
Replacing a window is notifiable work, and the standard applied to it is stricter than the one applied to a new house. Since 15 June 2023, a replacement window in England must reach 1.4 W/m²K or Window Energy Rating band B. A new dwelling only has to clear 1.6 W/m²K today, tightening to 1.2 W/m²K under the Future Homes Standard from 24 March 2027. Approved Document F, updated on 15 June 2022, adds ventilation on a no-worse-than-before basis: about 8,000 mm² of equivalent area for a habitable room and 4,000 mm² for a wet room, which in practice means most replacements carry trickle vents. The Part L rules for replacement windows set all of this out in detail.
The practical point is that the floor is not where you should be buying. Moving a window from a lower band up to band A costs roughly £0 to £50 per window, which on a ten-window house is £0 to £500 on a job of £5,000 to £12,000. Band A means an Energy Index of 0 or better and a U-value of about 1.2 to 1.4; band A+ and A++ go further but generally need triple glazing, which carries a 10 to 20% cost premium of its own.
Scoping the job: how many windows, and where
Replacement is priced per window but bought as a job, so the count matters. Doing the whole house at once spreads one survey, one delivery and one crew visit across every opening; phasing repeats all three. The table below is what a full fitted uPVC replacement runs by property type.
| Property | Windows | Low | Average | High |
|---|---|---|---|---|
| Flat | 4 | £1,800 | £3,200 | £5,000 |
| Bungalow | 8 | £3,500 | £5,500 | £8,000 |
| Mid-terrace / 3-bed | 8–10 | £4,000 | £6,500 | £10,000 |
| Semi-detached | 10–12 | £5,000 | £8,000 | £12,000 |
| Detached | 12–16 | £7,000 | £11,000 | £16,500 |
Source: DGCC 2026 dataset. uPVC casement throughout. Aluminium adds 30 to 40% and timber 60 to 110%.
Region moves these numbers more than any other input the job has. The same replacement is about 20% above the UK average in London and 15% above in the South East, 5% above in the South West, on the benchmark in the Midlands, and below it in the North West (-7%), Scotland (-8%), the North East (-9%) and Wales (-13%). Our regional cost breakdown and cost by house size pages carry the full tables, and the uPVC window calculator will price your own count, style and region in about a minute. If you are replacing only part of the house, write down the frame colour, glass specification and hardware now so the later batch still matches, and keep an eye on the full cost picture before you commit to a sequence.
How long a replacement takes
Allow 3 to 6 weeks between accepting the quote and the fitters arriving. Almost all of that is manufacture lead time, because replacement units are made to the survey measurements rather than pulled off a shelf. The fitting itself is short: 1 to 2 days for a standard house, about a day for a small flat of 4 to 6 windows, and 3 to 7 days for a large or bespoke job. The crew works opening by opening, so the house stays secure overnight. The step-by-step installation process covers each stage, and what to expect on installation day covers the preparation you need to do first.
What to check in a replacement quote
Three quotes are only comparable if they describe the same job. Match the unit count and dimensions, the frame colour and finish, the glass specification (A, A+ or A++ and the gas fill), the hardware, the trickle vents, whether removal and disposal are included, and whether making good is included. A price well below the others is almost always a specification downgrade hidden inside rather than a better deal. Check the firm's FENSA or CERTASS registration number, the deposit terms, the guarantee length and whether an Insurance-Backed Guarantee comes with it, because a company guarantee is worth nothing if the company stops trading.
Paste a quote into the quote quality auditor to benchmark the per-window figure against the 2026 dataset and flag what the document does not say. Our guides on getting three quotes and avoiding being overcharged cover the sales tactics worth recognising, including the same-day discount that was never a discount.
The quotes we check almost never state what is being replaced. A homeowner swapping 20-year-old double glazing is shown the same energy saving as one still on single glazing, and it is not the same job. If a salesperson quotes you £85 a year without asking what is in your openings now, they are reading a script rather than pricing your house.
Double Glazing Cost Calculator Team
Frequently asked questions
A fully fitted uPVC replacement window costs £400 to £1,000, averaging around £650. Aluminium runs 30 to 40% above uPVC and timber 60 to 110% above it. Across a whole house, expect £1,800 to £5,000 for a flat of 4 windows, £5,000 to £12,000 for a semi of 10 to 12, and £7,000 to £16,500 for a detached of 12 to 16.
The energy case is much weaker than replacing single glazing. Single glazing sits at about 4.8 to 5.8 W/m²K and pre-2002 double glazing at about 2.8 to 3.2, against 1.0 to 1.4 for a modern A-rated unit. The Energy Saving Trust's £85 a year for a typical Great Britain semi is measured against single glazing, so a second-generation replacement saves considerably less. The usual reasons to go ahead are a frame at the end of its 20 to 25 year life, repeated sealed unit failures, draughts, security or noise.
The window itself is only about 40 to 55% of the fitted price. The rest is roughly £300 to £600 per window of labour covering the survey and measurement, removal and disposal of the old window, fitting and sealing, trickle vents and hardware, and the FENSA or CERTASS certificate. Making good the plaster around the reveal is the line most often left out, so check the quote names it.
Yes. Since 15 June 2023 a replacement window in England must achieve a U-value of 1.4 W/m²K or a Window Energy Rating of band B or better. Since the 15 June 2022 update to Approved Document F, most replacements must also carry trickle vents, on a no-worse-than-before basis. The installer is legally responsible for compliance and self-certifies the work under a Competent Person Scheme.
Allow 3 to 6 weeks from accepting the quote to the fitters arriving, almost all of it manufacture lead time on made-to-measure units. The fitting itself is 1 to 2 days for a standard house, about a day for a small flat of 4 to 6 windows, and 3 to 7 days for a large or bespoke job.
Doing the whole house in one visit is cheaper per window, because the survey, the delivery and the crew's travel are spread across every opening rather than repeated. Phasing makes sense when cash flow rules out the full job or when only part of the house is failing. If you phase, keep the frame colour, glass specification and hardware written down so the later batch matches.
Yes, and by more than any other single input. The same job is about 20% above the UK average in London and 15% above in the South East, but 7% below in the North West, 8% below in Scotland and 13% below in Wales. The Midlands sits on the national benchmark.