Double glazing cost: what the job involves and who is registered to do it

the UK roofing register

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How windows and doors works

1. Count the openings, not the rooms. Glazing is priced per aperture. A bay counts as several, a fixed pane costs less than an opener, and a door in a window run is priced separately again. A survey that lists every opening with its size and whether it opens is the only version of a quote you can compare against another one, and it is the thing to ask for before any discount is discussed.
2. Fix the frame material before you compare anything. uPVC, aluminium and timber are three different products at three different prices, with different sightlines, different lifespans and different maintenance. A cheaper quote in aluminium and a dearer quote in uPVC are not the same job made cheaper, and comparing the totals tells you nothing until the material and the profile are the same on both.
3. Ask what happens to the reveal, the sill and the plaster. Taking a frame out disturbs everything around it. Whether the quote includes making good internally, a new sill, cavity closers and external sealing is the single commonest reason a finished job costs more than the number that was agreed. It is a line item, and it should be written down rather than assumed.
4. Check the certificate is included. Replacing a window in England or Wales is notifiable building work. An installer registered on a competent person scheme certifies its own work and registers it, which is included in the price. An unregistered installer means you notify building control and pay for the inspection separately, so the cheaper quote can carry a cost the dearer one already covers.
5. Read the ventilation and the safety glass lines. Replacement windows have to keep the ventilation the room already had, which in practice usually means trickle vents in the new frames. Glazing in a critical location, low down or beside a door, has to be safety glass. Both are requirements rather than upgrades, and a quote that offers either as an extra has not priced the job properly.

Insurance and paperwork

Common questions

Why do double glazing quotes vary so widely for the same house?

Because they are rarely the same specification. Frame material, profile depth, glass unit make up, hardware, whether the fitters make good afterwards and whether the certificate is included all move the total, and none of them is obvious from the headline figure. Ask each firm to quote the same written schedule and the spread narrows sharply.

Is it cheaper to replace just the glass rather than the whole window?

Often, yes, and it is a different job. If the frames are sound and only the sealed units have failed, a glazier replaces the units and leaves the frames alone. If the frames have dropped, rotted or lost their seals, replacing glass into them buys very little time.

Does the price include taking the old windows away?

It usually does, but it is worth reading rather than assuming, along with who is responsible for scaffolding or access equipment on upper floors. Those two lines are where quotes most often quietly differ.

Do I need permission to replace windows?

In most houses no planning permission is needed, but the work is still notifiable under the Building Regulations, and a listed building or a conservation area changes the answer completely. Ask before the survey rather than after the order.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area