Sash Window Replacement Cost in London: 2026 Price Guide

The cost of replacing a sash window in London moves by a factor of four, and the thing that moves it most is not the glass, the timber or the borough. It is whether the box frame built into your wall is staying or coming out.

You can settle that yourself, in an afternoon, with a bradawl and a torch. Do it before you invite anyone to quote and you stop comparing prices for jobs that were never the same job.

Settle the box frame question first

The box frame is the case built into the wall opening: two pulley stiles, the outer and inner linings, the head, and the cill underneath. The sashes slide inside it. Replacing sashes is joinery delivered to your house. Replacing the box is building work, because it is bedded against the brickwork, plastered up to, and in most Victorian and Georgian houses carrying the internal shutter boxes as well.

Go round each window in turn.

1. Open the bottom sash and prise off the staff bead on one side. It is the moulded bead holding the lower sash in, and a stiff putty knife worked behind it will lift it if the paint is not solid.
2. Push a bradawl into the bottom 150mm of the pulley stile you have just exposed, at roughly 45 degrees, at three or four points. Sound softwood stops the point in the first 2mm or 3mm. Timber that swallows it to 10mm and beyond on hand pressure alone has gone.
3. Probe the cill along its front edge and, more importantly, underneath it at both ends. That is where water sits and where nobody looks.
4. Probe the outer lining where it lands on the cill. That joint stays damp longest.
5. Grip the meeting rail and the bottom rail of the sash and try to push it out of square. If the corners visibly shift, or a black line opens along the shoulder, the sash joints have let go.

Then read the pattern rather than counting the soft spots. A soft cill and soft pulley stile feet on the same window mean the box is failing, and new sashes would be money hung on a frame dying behind them. A sound box with tired sashes is the ordinary London case, and it is by a wide margin the cheaper one.

What comes out of the wall, and what it costs

Those are 2026 figures from competent London joinery firms, for a standard domestic window of roughly 1.5m by 0.9m with reasonable access. A bay of three, a first-floor window over a basement lightwell, or anything above 2m sits at or above the top of its band.

Draw a line under the third row. Below it you are buying a replacement window, which is a controlled fitting under the Building Regulations. On that row and above it you are buying repair or reglazing, which is not. That line decides what glazing you are permitted to specify.

Most London jobs land on the third row, because leaving a sound box where it is avoids masonry and plastering you would otherwise pay for twice. uPVC or aluminium in a sash pattern sits at the bottom on price and is a separate argument about what you own afterwards, which we go through in uPVC sash windows against original timber.

Why one window costs twice what its neighbour does

Height, more than width. A 2.2m Georgian first-floor sash is not twice the price of a 1.1m bedroom window, it is nearer three times. Heavier sections, bigger weights, and two people on every lift.

The glass. Single glazing is cheapest and lightest. Slim units with krypton fill cost real money, and vacuum units more again. On a double glazed sash the glass alone can be a third of the price of the window, which is why the full double glazing price breakdown is worth reading before you specify anything.

Condition of what stays. If the box is sound, new sashes go straight in. If the pulley stiles are soft at the foot and the cill has gone, you are in new-frame territory whatever the original plan was, and the price roughly doubles.

Where the van goes. Loading a five-metre box frame in a controlled parking zone with no bay to suspend means a permit, a suspension, or two extra men and a circling van. Some firms price that as a separate line, some bury it in the rate. Either is honest as long as you are told which.

Ironmongery. Fitch fasteners, Brighton bolts, sash lifts and pulleys in solid brass rather than pressed steel add roughly £80 to £250 a window. Cast pulleys running on steel axles corrode and seize; brass wheels on brass axles do not.

Decoration. Almost every timber window quote includes prime and undercoat only. Two full finishing coats on site is another £240 to £520 a window in London, and it is not optional. A primed window left through a London winter starts taking up water immediately.

Access, and the arithmetic outside the window

Scaffolding is not really a weekly rate, whatever a first quote implies. Domestic scaffold is priced as a job: erect it, leave it standing for an agreed period, take it down. For a single two-storey elevation on a London terrace that job price usually lands around £900 to £1,800, with four to eight weeks of hire inside it, and a charge for every week beyond. Ask what the included period is and what an over-run costs, because that is where the surprise lives. A four-storey townhouse front means more lifts, more ties and usually a pavement gantry, and will cost more than several of your windows put together.

The highway licence. If the scaffold stands on the pavement or overhangs it, section 169 of the Highways Act 1980 makes it unlawful to erect or retain it without a written licence from the borough as highway authority. The Act allows any person to apply, but in practice the licence sits with your scaffolding contractor, because boroughs attach conditions a householder cannot meet. Islington, to take one, requires confirmation of public liability cover of £10 million or more.

Fees are set borough by borough. Islington charges a refundable deposit per pole placed on the highway plus a management fee, and issues licences for up to three months, with any extension applied for at least fourteen days before expiry. Others use a flat fee banded by the scale of works. What catches people out is not the fee but the renewal: a fixed-term licence on a job that over-runs has to be extended, which is a solid reason not to accept a vague programme.

Parking bay suspension. Borough-set, charged per bay per day, and needed for any delivery of long timber.

Making good. Taking out a box frame disturbs plaster, architraves and often the internal shutter boxes. Plastering, mouldings and internal painting are frequently excluded from a joinery quote. Ask, in writing.

Lead paint. Assume the lower coats on any London window decorated before the 1970s contain lead. White lead was still going into wood primers into the early 1960s, and lead paint was not withdrawn from general sale in Britain until 1992. Dry sanding and burning off release lead dust and fume, so wet abrasion, chemical stripper or an infrared plate are the sensible routes, and stripping adds time to any quote that includes it.

VAT, and the two rates that are not 20%

Most sash window work in a normal occupied home is standard-rated at 20%. Prices in this article, and in most trade quotes, are shown excluding it, so add a fifth to everything before you set it against your budget.

Two exceptions are worth knowing. If the property has not been lived in for at least two years immediately before the work starts, the renovation can qualify for the reduced 5% rate under HMRC's construction rules, and the test is when the premises were last lived in rather than when you bought them. On a whole-house job that is a five-figure difference, and it is the largest single saving available on this kind of work.

The other is a myth worth killing. If anyone tells you listed buildings are VAT-free, they are working from old information: the zero rate for approved alterations to protected buildings was withdrawn on 1 October 2012. Listed status now changes what you are allowed to do, not what you pay in tax.

Two houses, costed line by line

A three-bed Victorian terrace. Eight sashes, boxes sound.

Ten to fourteen weeks, most of it lead time on the joinery rather than men on site.

Now price the same eight windows the other way. A full overhaul with draught proofing and splice repairs at £1,200 a window is £9,600, with the same £2,800 of decoration and the same £1,200 scaffold: £13,600 before VAT, or £16,320 delivered. That is £2,880 less, and it keeps original timber that is denser and slower grown than the joinery redwood on sale now. What it does not get you is double glazing. Judge the two on what you are actually buying rather than on the bottom line; the room-by-room restoration budget works the overhaul route out in detail.

A four-storey Georgian townhouse. Sixteen windows, conservation area. Full replacement is not realistic here, on cost or on consent, so this is new sashes into the original boxes with the boxes repaired in situ.

The scaffold line is the one that swings, because a sixteen-window programme keeps a gantry standing for months and the licence has to be renewed inside that. Note what is not in the table: the planning application has to be determined before the joinery is ordered, and between consent and lead times the job occupies most of a year.

Neither budget is a quote. They are the shape of the thing, so you can tell whether what lands on your doormat is plausible.

What the regulations let you buy

Replacing a whole window, frame and all, makes it a controlled fitting. Approved Document L sets the limiting standard for a window in an existing dwelling at a U-value of 1.4 W/m²K, or a Window Energy Rating of Band B. Timber windows had a concession allowing 1.6 or Band C, and it expired: from 15 June 2023 the full standard applies to them too. That is why a genuine replacement is nearly always double glazed, and it is a cost driver in its own right.

Keep your box frame and the position reverses. Approved Document L defines a controlled fitting as the entire unit of a window including the frame, and says plainly that replacing glazing, or a window in its existing frame, is not providing a controlled fitting and does not have to meet the energy efficiency requirements. That is the legitimate route to keeping single glazing or very slim units in a period house. It is also why re-sashing does not come with a FENSA certificate, since FENSA and Certass cover replacement windows rather than repairs or reglazing. There is more in our guide to which regulations apply when you repair or replace.

One further provision is worth knowing if you are being pushed towards a specification you do not want. Where windows cannot meet the standard because of the need to maintain the character of the building, Approved Document L accepts either a centre-pane U-value no worse than 1.2 W/m²K, or single glazing supplemented with low-emissivity secondary glazing. Work to listed buildings, buildings in conservation areas and scheduled monuments does not have to comply fully where doing so would unacceptably alter character or appearance, and building control is told to consider the conservation officer's advice.

Planning is a separate question and usually the binding one. Listed building consent is needed for works affecting a listed building's character, and windows almost always affect character. In a conservation area with an Article 4 direction, permitted development rights for windows have been withdrawn and you need permission even for like-for-like timber. Flats and maisonettes have no householder permitted development rights at all, so a window change to a flat generally needs an application whether or not the building is listed. Householder applications carry a statutory eight-week determination period from validation, and a refusal arriving after you have paid a deposit on joinery is an expensive way to learn this. Our guide to windows in conservation areas sets out what the boroughs actually look for.

The order to do this in

Sequence saves more on this job than negotiation does.

Count the windows properly first, including the half-landing and every light in a bay, because bays are priced individually and people forget them. Then do the bradawl round from the top of this article and write a verdict beside each one: box sound, box doubtful, box gone. That single sheet of paper is what turns three incomparable quotes into three prices for the same work.

Ring the borough's planning department next, before you spend anything on drawings or deposits, and ask two things: whether your street is covered by an Article 4 direction, and whether the building is listed. Both are free to ask and either can stop the project.

Only then get three quotes against that one written scope, and make each firm answer four questions on paper: what the scaffold price includes and what an over-run costs, who applies for the highway licence, what happens to the price if hidden decay is found once the sashes are out, and whether VAT is shown and at what rate. A firm that answers all four is worth more than one that is £2,000 cheaper and answers none.

If you would rather someone else made the call on the box frames, our sash window restoration work prices the repair route against the replacement route so you can see both numbers side by side, and the wider sash window repair service covers every London borough. A window that turns out to need specific repairs costed individually is often a far smaller job than the first quote suggested.