Almost all the worry that goes into new windows lands on the window itself. Which timber, which finish, which glazing unit, which handle. On site, the joinery is rarely the part that decides whether the job feels like money well spent. A timber window installation is a sequence of structural judgements dressed up as carpentry, and most of them are made at the survey, at the fixing stage, and in the two hours after the old frame comes out. None of that shows up in the finished photograph.
What follows is the sequence as it actually runs in a British house, including the parts installers tend not to talk about until the dust sheets are down.
Past the research stage already? Have a look at the window range we build, or send us your opening sizes and we will come back with a quote.
The survey decides more than the window does
A proper survey is not someone with a tape measure writing down three numbers. It is a set of decisions about the opening, and those decisions travel all the way through to the day the scaffold comes down.
The surveyor should be working out whether the structural opening is square, how far out of plumb the jambs run, whether the existing lintel is doing its job, what condition the internal reveals are in, and whether the sill sits on brick, on stone, or on something soft that will need rebuilding. Older British openings move. A Victorian bay that reads 1,200 mm at the head and 1,186 mm at the sill is unremarkable, and the frame has to be made for the tighter dimension with a workable tolerance around it.
The reveals are where surveys go quiet. Lever off a strip of architrave on a north elevation and the timber behind it can be dark and soft enough to mark with a thumbnail. That is not a window problem, but it becomes a window problem on the day of fitting, because someone has to price the repair and someone has to do it.
Two things worth settling in writing at survey stage: who makes good the internal plaster, and what happens if the opening turns out to be worse than it looked. Both are common sources of friction on an otherwise clean job.
Four routes into the same opening
British houses get windows replaced in more than one way, and the route chosen changes the cost, the mess and the compliance route. Worth knowing which one you are buying.
| Route | What it involves | Weak point | Who it suits |
|---|---|---|---|
| Full frame replacement | Old frame out completely, new frame fixed to the structure, new sill and seals | Internal making good, plaster lines and architraves | Most post-war and Victorian casement openings |
| Box sash replacement | Entire box, linings and sashes replaced with a new unit | Deep reveals and internal linings usually need rebuilding | Period terraces where the box has gone soft |
| Sashes only, box retained | New sashes and draught-proofing into the sound existing box | Frame stays as it is, glazing options limited by the rebate | Listed and conservation properties, sound original boxes |
| New opening or new build | Frame fixed to structure before plastering, protected through the wet trades | Site damage before handover, coordination with the build programme | Extensions, self-builds, full refurbishments |
If your property is listed or sits in a conservation area, the "who it suits" column above is not the whole story. Consent shapes which route is even available to you, and that is a separate conversation with the officer: we cover it in what conservation officers actually approve.
How long a timber window installation leaves the house open
This is the question homeowners ask least often and worry about most. The honest answer is that the opening is only exposed for as long as it takes to get the new frame in, and a competent team works one opening at a time for exactly that reason.
On a straightforward casement replacement, the old frame comes out and the new one goes in and is made weathertight within the same working day. Larger openings, bays and box sashes take longer, and on a bay it is normal to see temporary props go in before anything is cut, because the structure above may be sitting partly on the frame you are removing.
What a good installer does when the weather turns: works to a sequence that never leaves more openings out than can be closed before the end of the day, boards and sheets anything that has to stand overnight, and does not remove a frame at four in the afternoon in November because the van is loaded. That last one is a scheduling decision, not a skills decision, and it is worth asking about before booking.
Factory-finished, pre-glazed units help here, because there is nothing to paint, cure or glaze on site. It is also where the trade-off sits. A unit that arrives finished cannot be trimmed and touched in on the spot: if a frame is damaged in transit or an opening was measured wrong, that is a re-order and a return visit, not an afternoon with a plane and a brush. Site-finished joinery is more forgiving on the day and usually less durable afterwards, because paint applied in a dusty room in British humidity does not behave like a factory coating.
The mess nobody photographs
Ripping out an old frame is destructive work. Plaster keys into the reveal, and plaster does not let go politely. The old frame often comes away with a fist-sized lump of it still attached, and on a box sash the internal linings usually come out with the box.
None of this is a sign that something went wrong. It is the normal condition of removing something that was plastered into the wall eighty years ago. What separates a good job from a bad one is that it was priced and explained beforehand: plaster cut back to a clean line, new timber liners fitted where needed, architraves either reused or replaced, and a stated finish level. "Making good" can mean anything from a rough fill to a plaster finish ready for paint, and those are very different amounts of work.
Agree the finish level in the quote. If the answer is vague, that is your answer.
If you are working out which system suits your openings, the product range lists frame depths and glazing options, and we are happy to look at a drawing.
Fixings, packers and the perimeter: where installations actually fail
When service calls come back to us on windows made years ago, the fault sits in the perimeter far more often than in the joinery. Two patterns come up repeatedly: a sash that has dropped a couple of millimetres because there was no packer under the hinge side carrying the load, and a draught traced to a perimeter filled with expanding foam and nothing else.
Three things a fitter should be doing at this stage:
- Fixing to structure, not to foam. Frame fixings or straps into masonry at sensible centres, with the frame packed at every load point so the fixings are not pulling the profile out of shape as they tighten.
- Sealing tighter inside than outside. An airtight seal on the internal face and a weather-resistant, vapour-open detail externally. Foam is insulation, not a seal, and on its own it lets moist indoor air travel into the joint where it condenses.
- Keeping the drainage path clear. Drainage slots in the frame and the external sill have to run to daylight. Sealant piped over a drainage slot is a slow leak with a delayed start.
Ask to see the perimeter before it is covered. It takes thirty seconds and it is the one stage you cannot inspect afterwards.
Ventilation: the Part F conversation
Replacing a window does not let you reduce the background ventilation the room already had. That principle sits in Approved Document F, which applies in England, with equivalent guidance in Wales, Scotland and Northern Ireland. How you satisfy it depends on the ventilation system the house actually has: where the dwelling relies on background ventilators and extract fans, vents in the new frames are the usual route, while a house running a whole-house mechanical system is a different conversation. Historic and listed buildings are handled differently again, and that is a question for Building Control rather than for a salesperson.
Where trickle vents are the route, owners of period properties usually dislike them on sight, and the objection is aesthetic rather than technical. On timber joinery the vent can be routed into the head of the frame and fitted with a canopy finished in the frame colour, which puts it above eye level and out of the sight line from the street. It is not invisible. It is considerably less obtrusive than a bright white plastic bar sitting on a heritage frame.
The physics argument for it is straightforward: a sealed, well-fitted window traps the moisture your household produces, and that moisture has to leave somewhere. If you want the longer version, see why condensation appears and what to do about it.
U-values and who signs the work off
Thermal performance for replacement windows in existing dwellings in England is governed by Approved Document L, which sets a limiting whole-window U-value of 1.4 W/m²K for a replacement window, with Band B on the Window Energy Rating scale as the alternative compliance route. The other UK nations set their own figures, and the Approved Documents are amended periodically, so check the edition in force for your project.
That figure is a ceiling, not a target. Argon-filled triple glazing in a deeper timber profile sits well below it: our 92 mm system reaches Uw 0.78 W/m²K, and the 115 mm system with quadruple glazing reaches Uw 0.6 W/m²K. Whether the extra pane is worth paying for is a separate question, and we have argued both sides in triple versus quadruple glazing.
On sign-off, the mechanism in England and Wales is that the installing company either belongs to a competent person scheme and self-certifies the work against the Building Regulations, or the work is notified to Building Control before it starts and inspected. This is an installer obligation, not a manufacturer one: a joinery works cannot certify an installation it did not carry out. If you are buying supply-only and using your own builder, establish which of the two routes applies before the first frame comes out. Retrofitting a notification afterwards is awkward and occasionally expensive at the point of sale.
Why two quotes for the same window differ by multiples
Homeowners often send us two prices for what looks like an identical specification and ask which one is wrong. Usually neither is. The spread comes from a handful of variables that do not appear on the quotation.
- Sash mass. A triple-glazed sash weighs several times what a single-glazed one does. Weight drives the hinge specification, the fixing pattern and the number of people needed to lift it into the opening. A quote that has not accounted for the weight will be cheaper, and will show it a few winters later, when the sash starts catching on the frame.
- Hardware rated to that mass. Multi-point locking and hinges come in load classes. Specifying to the class above adds cost and adds the years back at the other end.
- Timber preparation. Laminated, kiln-dried engineered sections cost more than solid softwood and move less through a damp British winter. That difference is invisible on the day of delivery and very visible after the third heating season.
- Finishing. A multi-coat waterborne finish applied in a controlled factory environment is a different product to two brushed coats in a customer's front room, and it is priced accordingly.
- What the installation line actually covers. Access equipment, waste removal, new sills, internal making good, decorating, temporary boarding. Two quotes can be identical on the joinery and thousands apart on this line alone.
We deliberately do not publish per-window prices, because a number without an opening size and an access description is misleading. For the ranges and what moves them, see our breakdown of timber window costs, U-values and wood types.
The first year, and what needs adjusting
New timber joinery settles. Hinges and keeps are designed to be adjustable for exactly that reason, and a sash that needs a slight lift on the hinge side after the first winter is normal maintenance rather than a defect. Most reputable installers will come back once in the first twelve months to adjust and check.
Two habits that protect the work: keep the drainage slots clear when you clean, and do not let a decorator paint over hinges, seals or vents when the reveals get finished. A gasket sealed shut with emulsion stops working as a gasket. Everything else is a straightforward routine, which we set out in the maintenance guide.
We build in Kalnciems, ship to 19 countries and hold Secured by Design accreditation for the British market, and the frames leave the factory finished and glazed. The thing worth pinning down before you sign anything is what happens after handover: who comes back for the first adjustment, how a hinge or a keep gets sourced five years from now, and whether any of that is written down rather than promised on the driveway.
Questions we get asked before the fitters arrive
How long will my house be open to the weather?
One opening at a time, and normally closed the same working day. A standard casement is out and the new frame in and weathertight within hours; bays and box sashes take longer and may need temporary props before anything is removed. Ask your installer directly how many openings they intend to have out at once, since that is the number that actually governs your exposure.
Do I need to be at home for the whole installation?
Not for the whole job, but be there at the start of the first day and at the end of the last. The first morning is when any surprises in the opening come to light and when decisions about making good get made. The final walk round is when you agree the snagging list while the team is still on site, which is considerably easier than raising it by email a fortnight later.
Can new timber sashes go into my existing frames?
If the boxes are structurally sound, yes, and it is a common route in period properties where consent restricts what can be changed. The limitation is the rebate: an old box was not made to carry a modern insulating unit, so glazing options are narrower and the frame itself keeps whatever thermal performance it already had. It is a sensible compromise on a listed elevation and a poor one if the boxes are already soft.
Who pays if the plaster around the reveal breaks up?
Whoever the contract says, which is why it belongs in the quotation rather than in a conversation on the day. Some plaster damage is unavoidable on removal, so the useful question is not whether it will happen but what standard of making good is included: cut back and filled, or finished ready for decoration. Those are different jobs at different prices.
How soon can the reveals be decorated?
Fresh plaster needs to dry before it is painted, and the timescale depends on thickness, the season and how well the room is ventilated. Factory-finished frames themselves need nothing, so the wait is about the wall, not the joinery. Resist the temptation to seal the room up to speed things along, since drying plaster releases a lot of moisture and it has to go somewhere other than your new glass.
Worth reading next
- Timber window costs, U-values and wood types if you are still comparing quotes and want to know what moves the number.
- Listed building window replacement if consent, not specification, is the thing standing between you and a decision.
- Timber window maintenance for the routine that keeps the joinery going for its full service life.
When you have your opening sizes, send them over and we will tell you what is realistic.
Windows Latvia, Kalnciems factory
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