How Much Do Double Glazed Windows Cost in 2026?

The price depends mainly on how many windows you're replacing, what frame material you choose, and the glass spec. A single standard uPVC casement window typically costs £350 to £600 supply and fit. Replacing all windows in a 3-bedroom semi-detached with uPVC frames averages £3,500 to £7,500. Aluminium frames cost considerably more - a full house replacement usually runs £6,000 to £12,000.

Double glazed windows cost £350 to £600 per window for a standard uPVC casement, £550 to £1,100 in aluminium, and £650 to £1,400 in timber, all supply and fit. A three-panel uPVC bay window is £800 to £1,500 because it is bigger and takes longer to fit properly. Across a whole house, most jobs land between £3,000 and £8,000. Ask every installer for a per-window breakdown rather than one total figure. It makes quotes far easier to compare.

A 3 bed semi with 8 to 12 windows costs £4,000 to £7,000 to do in uPVC, supply and fit. A 3 bed detached usually has 10 to 14 windows and comes in at £5,000 to £9,000. Count every opening in the house before you ask for quotes, including the landing, bathroom, and anything in a porch, because the window count drives the total far more than the number of bedrooms does. Bay windows and any upstairs opening that needs scaffolding will push you towards the top of the range.

Expect £6,000 to £12,000 for a 4 bed detached in uPVC, based on 12 to 18 windows supplied and fitted. Aluminium frames cost 50 to 80% more than uPVC, so the same house in aluminium is a much bigger number. On a job this size the per window price has room in it, so get three quotes and ask each installer to break the price down opening by opening rather than handing you a single total.

If you buy the windows yourself and pay an installer for fitting only, you can expect to take roughly 30% off a supply and fit price. It is only worth doing if you are confident about the measurements, because made-to-measure windows cannot be returned if the sizes are wrong. Agree in writing who carries the cost if a unit turns up damaged or does not fit, and check the fitter can still register the work for a FENSA certificate.

For most homes, replacing windows is permitted development - no planning permission needed. If you're in a conservation area, AONB, or a listed building, check with your local council before ordering anything. The style, material, and colour of the windows may be restricted to match the character of the area. Whatever your planning status, windows have to meet Building Regulations Part L for energy efficiency and Part Q for security - a FENSA-registered installer deals with this for you automatically.

The sealed glass units in good quality double glazing typically last 20 to 35 years before they start to fail - condensation between the panes is the usual sign. uPVC frames hold up well but can yellow and go brittle after 20-odd years in direct sunlight. Aluminium frames age more gracefully and tend to last longer. Worth knowing: if your frames are still sound, you can often just replace the glass units rather than the whole window, which is considerably cheaper.

uPVC is the most common choice in the UK for good reason - it's affordable, low maintenance, and performs well thermally. Aluminium costs 50 to 80% more but the difference in appearance is noticeable: slimmer frames, sharper sight lines, and a look that suits modern and contemporary homes much better than uPVC. It also holds its colour and shape over time. For most Victorian and Edwardian semis though, uPVC does the job and nobody can tell the difference from the street.

For most UK homes, triple glazing isn't worth the extra cost. The UK climate simply isn't cold enough for the additional pane to pay back in energy savings - we're not Norway. Triple glazed units also weigh considerably more, which puts extra strain on hinges and frames over time. That said, if you're on a particularly exposed or cold site, or noise is your main concern rather than heat loss, there's a reasonable case for it.

FENSA is the government-authorised scheme that lets registered installers self-certify their work complies with Building Regulations, so you don't have to involve the council. Once the job is done, you get a FENSA certificate. Hang on to it - solicitors ask for it when you sell. Without it you'd have to apply to your local council for retrospective approval, which is a headache nobody needs. Check your installer is registered before you sign anything: fensa.org.uk.

Switching from single glazing to A-rated double glazing saves around £140 a year on energy bills for a typical semi, and more for a detached home, according to the Energy Saving Trust. Replacing old double glazing with new units is less dramatic - expect £30 to £100 a year depending on what you're starting from. Honestly, most people notice the draught reduction and the quieter rooms more than the bill saving. The financial payback takes years either way, but the comfort improvement is immediate.

January and February are the quiet months, and the big national companies know it - that's when they run their biggest promotions. Independent local installers are also more flexible on price when their order books aren't full. Summer is the most expensive time. Autumn can be decent value too. One more thing: those 'today only' offers that salespeople push are rarely today only. Take your time, get multiple quotes, and don't let anyone pressure you into signing on the day.