This page gathers the questions we are asked most about double glazing, with short, factual answers and 2026 figures. The numbers are cross-checked across Checkatrade, the FMB, GreenMatch and installer guides. For a tailored estimate, put your own details into the uPVC window calculator, or start with our cost per window guide.
Questions and answers
How much does it cost to replace all windows in a house?
Most UK homeowners pay between £4,000 and £10,000 to replace all windows in an average semi-detached house in 2026. A flat might cost £1,800 to £5,000, while a large detached home can reach £7,000 to £16,500 or more, depending on the number of windows, frame material and glazing. See the full breakdown in our cost by house size guide.
Is uPVC cheaper than aluminium?
Yes. uPVC is the most affordable frame material, typically around 35% cheaper than aluminium and roughly 90% cheaper than timber, while still delivering excellent thermal performance. Aluminium costs more but offers slimmer frames and a sleek, modern look.
Is triple glazing worth the extra cost?
Triple glazing adds roughly 20 to 30% to the price. It improves insulation and noise reduction, making it most worthwhile in colder regions, near busy roads, or for very energy-conscious homes. For many homes, good-quality A-rated double glazing offers the best value.
How long does double glazing installation take?
A typical installer fits 4 to 6 windows per day, so an average house is usually completed in 1 to 3 days. Larger homes or complex installs such as bay windows can take a little longer.
Do I need planning permission for double glazing?
Usually not. Replacing like-for-like windows falls under permitted development. However, listed buildings and homes in conservation areas often need consent, so always check with your local planning authority first.
How much can double glazing save on energy bills?
Replacing single glazing with A-rated double glazing can save up to around £140 a year on a typical semi-detached house, according to the Energy Saving Trust. The exact figure varies by house size, region and your current windows.
Are there any grants for double glazing in 2026?
The main routes have changed in 2026. ECO4 closed to new applications on 31 March 2026. In England, the Warm Homes: Local Grant is now the headline scheme, offering up to £30,000 for energy upgrades (including glazing) for lower-income households in EPC bands D to G. Scotland has Home Energy Scotland loans and grants, and only around 15% of households qualify for funding overall, so check eligibility before assuming free windows. Check what might apply to you with our grant eligibility checker.
How long does double glazing last?
Quality double glazing lasts around 20 to 25 years for uPVC frames, 30 to 40 years for aluminium, and 30 to 60 years for well-maintained timber. The sealed glass unit itself typically lasts 15 to 20 years before any misting. Most reputable installers offer a 10-year guarantee.
Should I get double glazing in winter or summer?
Installers are often quieter (and sometimes cheaper) in autumn and winter, so you may get better deals. Installation can be done year-round, because fitters only remove one window at a time, so your home is not left exposed.
How much does one double glazed window cost in 2026?
A typical A-rated uPVC casement window costs around £650 fitted in 2026, within a working range of £400 to £1,000 per window. That figure covers supply, labour, removal of the old window, sealing and the FENSA certificate. Sash, bay, aluminium and timber windows cost more.
How much does double glazing cost for a 3-bed house?
A 3-bed or mid-terrace house with 8 to 10 uPVC casement windows typically costs around £6,500 fully fitted in 2026, within a range of £4,000 for a basic specification to £10,000 for a higher one.
What U-value do replacement windows need to meet in 2026?
Under Approved Document L, replacement windows must reach a U-value of 1.4 W/m²K or lower and a Window Energy Rating of band B or better, which usually means an A-rated unit. Modern A-rated double glazing typically achieves 1.0 to 1.4 W/m²K.
What is the difference between supply-only and fully fitted?
Supply-only is just the window unit, from around £160 for a basic uPVC casement. Fully fitted adds labour, removal of the old window, sealing and the FENSA certificate. The gap is typically £200 to £600 per window, so always check which a quote refers to.
How much does aluminium or timber add over uPVC?
Aluminium runs roughly 30 to 40% above uPVC per window, and timber 60 to 110% above. A uPVC casement is £400 to £1,000 fitted, aluminium £550 to £1,300, and timber £900 to £2,000.
Has ECO4 closed?
Yes. ECO4, which once funded free double glazing for some households, closed to new applications on 31 March 2026. In England the Warm Homes: Local Grant is now the headline scheme, offering up to £30,000 of energy upgrades for lower-income households in EPC bands D to G until March 2028.
Still not sure whether a quote stacks up? Run the figures through our quote quality auditor, and read up on how to avoid being overcharged before you sign anything.