Double Glazing UK · FENSA & CERTASS Registered Installers
Replace your windows with a vetted, FENSA or CERTASS registered installer. A single uPVC window starts from £450 supplied and fitted, with A-rated glass, a Building Regulations certificate and aluminium and heritage options available. Compare itemised quotes before you book.
From a single replacement window to a whole-house uPVC reglaze or premium aluminium and heritage frames — vetted, FENSA or CERTASS registered installers for every job.
Per uPVC Window
Single Window
£450 – £900 fitted
A single replacement uPVC window, supplied and fitted with A-rated glass. The unit cost falls when you do several at once. Style, size and glass spec set the price.
A full reglaze of a typical semi-detached home in uPVC — the most popular choice. Usually one to two days on site and the best value per window across the property.
Slim aluminium or heritage and timber-effect frames for contemporary or period homes. Often made to measure with longer lead times, and the premium choice for looks and sightlines.
More openings mean more units and fitting time — but a lower unit cost
Frame material
+£100 – £400/window
Aluminium and timber cost more than uPVC for slimmer sightlines
Glass spec
+£50 – £250/window
A-rated, triple, acoustic or toughened glass adds to the unit price
Style & shape
+£100 – £500
Bay, sash, arched and shaped windows cost more than casements
Access & making good
Varies
Upper floors, scaffolding and reveals or plastering after fitting
A single uPVC window usually sits inside the £450–£900 range, and a whole-house uPVC reglaze of a semi £4,500–£8,500. London and the South East run higher. A full double glazing cost breakdown is in our cost guide.
Double glazing costs at a glance — 2026
Figures from this page's 2026 cost cards and cost-driver table.
Source: BestBuilders 2026 quote data · 519 UK towns
Why Choose BestBuilders
3 Steps to a FENSA-Registered Window Quote
1
Tell us about your windows
60-second form. The number of windows, the frame material you want, whether it is a full reglaze and your postcode. No phone, no jargon.
2
Get matched to installers
Up to 3 vetted, FENSA or CERTASS registered installers near you. We pre-screen on registration and reviews.
3
Compare & book
Itemised quotes within 24 hours. Compare the frame material, glass spec, guarantee and FENSA certificate before you book.
Glass & Frames
A-Rated Glass & Frame Materials (2026)
The glass and frame you choose drive both the look and the energy performance. Here is what to weigh up.
🪟 A-rated energy glass
A-rated double glazing uses a low-emissivity coating, an argon-filled gap and a warm-edge spacer to cut heat loss. Triple glazing goes further and helps with noise on busy roads.
🧱 uPVC — best value
uPVC is the most cost-effective and well-insulated choice, with low maintenance and a wide range of styles and colours. It suits the majority of UK homes.
🏙️ Aluminium — slim & modern
Aluminium frames are strong and slim, giving more glass and a contemporary look. They cost more but are ideal for large openings and modern extensions.
🏛️ Heritage & timber
Timber and heritage-style frames suit period and conservation-area properties where appearance matters, and modern timber-effect options keep maintenance low.
Certificates & Planning
FENSA Certificates & Conservation Areas
Replacement windows are covered by Building Regulations, and your registered installer self-certifies the work.
📜 FENSA / CERTASS certificate
A FENSA or CERTASS registered installer self-certifies the work against Building Regulations and you receive a certificate. This matters for your warranty and when you come to sell the property.
🏠 No planning permission (usually)
Replacing windows is permitted development in almost all cases. Your installer handles Building Regulations compliance through their registration.
🏛️ Conservation areas & listed buildings
Conservation areas and listed buildings may restrict changing the frame material or style and can need consent. Your installer will check before any work starts.
💰 Resale value
Energy-efficient, certified windows improve the EPC rating and reassure buyers — a FENSA certificate is one of the documents a conveyancer asks for on sale.
Local Double Glazing Installers
Double Glazing Installers by Town
Vetted, FENSA or CERTASS registered double glazing installers across UK towns:
In your area a single uPVC window costs roughly £450 to £900 supplied and fitted, a whole-house uPVC reglaze of a typical semi £4,500 to £8,500, and aluminium or heritage frames £8,000 to £18,000. The number of windows, the frame material and the glass spec drive the price.
Usually not. Replacing windows in your area is permitted development and is covered by Building Regulations through your FENSA or CERTASS registered installer. Listed buildings and conservation areas are the exception and may need consent, particularly for changing the frame material or style — your installer can check first.
Yes. The installers we match you with in your area are FENSA or CERTASS registered, so the work is self-certified against Building Regulations and you receive a certificate. This is important for warranties and when you come to sell the property.
A few windows in your area can be done in a day, and a whole-house reglaze of a semi usually takes one to two days. Aluminium and heritage installs can take a little longer because the frames are often made to measure with longer lead times before fitting.
It depends on budget and look. uPVC is the most cost-effective and well insulated, which suits most your area homes. Aluminium costs more but gives slimmer sightlines and more glass, ideal for contemporary extensions and large openings, while timber or heritage frames suit period and conservation-area properties.
Triple glazing adds a third pane and extra insulating gap, improving heat retention and reducing noise, but it typically costs around 1.5 to 2 times as much as double glazing. For most UK homes, good A-rated double glazing already performs well. Triple glazing makes most sense in very exposed locations, near busy roads, or in highly insulated new builds where the extra thermal performance is genuinely useful.
Windows carry an energy rating from the British Fenestration Rating Council, running from the lowest bands up to A++. The rating reflects how well the whole window retains heat, factoring in the glass, frame and any coatings. A-rated is a strong, common standard for replacement windows, while A+ and A++ offer even better thermal performance and can help lower heating bills in colder homes.
Quality double glazing typically lasts 20 to 35 years, with uPVC frames often outlasting the sealed glass units themselves. Signs a window is failing include misting between the panes, draughts, difficulty opening and stiff or broken hardware. Regular cleaning of frames, seals and drainage holes helps extend their life. Frames may remain sound long after the glazed units need replacing.
Misting or condensation between the panes means the sealed unit has failed and its insulating gas has escaped. Often just the glass unit can be replaced while keeping the existing frame, which is cheaper than a full window. If the frame is also worn, draughty or damaged, full replacement is usually the better long-term value. An installer can advise which option suits each window.
Replacement windows must meet Building Regulations. A FENSA or CERTASS registered installer can self-certify the work, so you avoid applying to building control separately. You receive a certificate confirming compliance, which is important when you sell your home, as buyers' solicitors routinely ask for it. Without it, you may face delays or need retrospective approval during the conveyancing process.
Replacing old, single-glazed or failing windows with modern energy-efficient double glazing reduces heat loss and draughts, which can lower heating bills and make rooms more comfortable. The saving depends on your current windows, home size and how you heat it, so homes upgrading from single glazing see the biggest difference. New windows also cut condensation and outside noise as an added benefit.
Casement windows hinge at the side or top and are the most common, affordable UK style. Sash windows slide vertically and suit period and traditional homes, though they cost more. Tilt-and-turn windows open inwards two ways, tilting for ventilation or swinging fully open for easy cleaning and escape. Your choice affects price, appearance and how well it fits the character of your property.
Yes. In listed buildings and conservation areas, replacing original windows is often restricted, so secondary glazing is a popular solution. It adds a discreet internal pane behind the existing window, improving insulation and reducing noise without altering the external appearance. It is usually reversible and less likely to need consent, but always check with your local planning authority before starting work on a protected property.
A U-value measures how much heat passes through a window: the lower the number, the better the insulation. Modern double glazing typically achieves a U-value well below older single glazing, and triple glazing lower still. U-value is a key part of a window's overall energy rating, so comparing it helps you judge how effectively different windows will keep warmth inside your home.
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