11 min read
The complete guide to replacement windows
The window industry is built on discounting, which makes real comparison hard. Comparing specification — frame, glass, hardware and making good — is the only way to see who is actually cheaper.
What windows cost
A typical three-bedroom house with 8–10 openings costs £5,500–£11,000 in uPVC and £9,000–£18,000 in aluminium, fitted and certified. Timber and aluminium-clad timber start higher and bring maintenance obligations.
| Frame material | Typical cost per window | Lifespan and maintenance |
|---|---|---|
| uPVC casement | £550 – £950 | 25 – 35 years, no painting |
| Aluminium | £850 – £1,450 | 35 – 45 years, slim sightlines |
| Timber casement | £900 – £1,600 | 40+ years, repaint every 5 – 8 years |
| Heritage / sash | £1,200 – £2,500 | Required in many conservation areas |
Reading the specification
Ask for the U-value of the whole window (not just the glass), the spacer bar type (warm edge or aluminium), the number of chambers in the frame, the hardware brand, and whether trickle vents are included. Two quotes with a £2,000 difference usually differ on at least three of these.
Since 2022, replacement windows generally require trickle ventilation. If a quote omits them, either the installer plans to add cost later or the installation will not comply.
Certification and building regulations
Replacement windows are notifiable work. A FENSA or Certass registered installer self-certifies and issues a certificate; otherwise you need a building control application. You will be asked for that certificate when you sell.
Making good — the part that is usually excluded
Removing a window damages the internal reveal and the external seal. Plastering, external sealant, sill replacement and painting are separate work items. Confirm which of them are in the price and who is doing the rest.
How to buy well
- Get three quotes on identical specification. Ignore any price that expires the same day.
- Do the whole house at once — the per-window rate improves substantially.
- Standard casement sizes are much cheaper than bespoke shapes, arches and bays.
- Ask for the deposit protection arrangement and check the company's registration.
- Look at the installer's last three local jobs rather than a national brochure.
Questions to ask builders
- What is the whole-window U-value, and which glass unit is specified?
- Are trickle vents included on every opening?
- Is internal plastering and external making good in the price?
- Will you provide a FENSA or Certass certificate?
- Who removes and disposes of the old frames?
- Is scaffolding needed and included?
- What is the manufacturing lead time and what is the deposit protection?
- What is the guarantee on frames, glazing units and hardware separately?
Warning signs in a quotation
- A price that halves during the sales visit.
- 'Show home' or 'this month only' discounts.
- Deposits above 25% with no insurance-backed protection.
- No U-value or glass specification anywhere in writing.
- Trickle vents missing from the quotation.
Frequently asked questions
How much do new windows cost for a whole house?
£5,500–£11,000 for uPVC across 8–10 windows in 2026; £9,000–£18,000 in aluminium.
Is triple glazing worth it in the UK?
For most homes the energy gain over good double glazing is marginal. The real benefit is noise reduction.
How long do windows take to install?
Manufacturing takes 4–8 weeks; fitting a whole house usually takes one to three days.
What certificate do I need?
A FENSA or Certass certificate, or a building control completion certificate if the installer is not registered.
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