Cost of new double glazing: what the job involves and who is registered to do it

How cost of new double glazing works

1. The frame system. This is the largest single line in most quotes. It covers the profile, its reinforcement, the finish, and the cills and trims that come with it. It is also where the visible difference between quotes lives, since a slim aluminium sightline and a bulky uPVC section can be described using very similar words.
2. The sealed units. The glass is priced by area and by specification. A low emissivity coating is now standard, an argon filled cavity is common, and toughened or laminated panes are required in critical locations rather than chosen. Acoustic and privacy glass are genuine upgrades with genuine costs.
3. The hardware. Hinges, handles, locks, restrictors and trickle vents are small parts that add up across a house and vary in quality far more than they vary in appearance. Hardware is also what fails first on a cheap window, so it is worth asking what is being fitted rather than accepting a general assurance.
4. The builder's work. Removal, disposal, cavity closers, new internal cills, plaster repairs at the reveal and external sealing. On a modern house this is modest. On a Victorian or Edwardian property with timber frames it can rival the cost of the windows themselves, and it is the line most often left out.
5. Certification and guarantee. A registered installer's price includes registering the notifiable work and issuing the certificate, and usually an insurance backed guarantee. Read what the guarantee actually covers and who underwrites it, because a guarantee from the installing company alone is only worth what that company is worth.

Insurance and paperwork

Common questions

Which line should I push on when negotiating?

None of them individually. Ask instead for the same written schedule to be priced by two or three firms. Negotiating a percentage off an unspecified job usually just moves specification rather than price.

Is triple glazing worth the extra on this list?

It changes the glass line and the frame line, since the unit is heavier and deeper. Whether that is worth it depends far more on the wall and roof insulation around the window than on the window itself.

What does an insurance backed guarantee actually do?

It is meant to cover the guarantee if the installing company ceases to trade. It is separate from the workmanship guarantee and from the manufacturer's product warranty, and the three are often presented as one thing.

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