These days double-glazed windows are pretty much standard. Mainly because the Building Regulations state new homes must have at least double-glazed glass. And, older properties install them when their single-glazed windows rot.
At present, the average cost of double-glazing in the UK is so reasonable that there’s no reason to miss out on their benefits. Typically, new windows cost from £400 to £600 for standard UK window sizes. And, an 8-window house costs around £4500 for uPVC replacement double glazed units.
But, what benefits do we get from installing double–glazed units? Probably, the most obvious is the savings on the monthly fuel bills. Smaller bills give us more disposable income. And it’s better for the environment. So, what’s not to like?
But, you must realise that double-glazing, or even triple glazing, won’t help you out if the remainder of your house isn’t fully insulated. Areas on which to focus include:
- Have at least 270mm loft insulation.
- External wall cavities need insulation.
- Fix draughts around doors, windows and chimneys.
- Double-glaze the front and back doors too.
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Topics
How Much Does Double Glazing Cost?
We’ve compiled the information in this article from many different online resources, to give you an overview of the best double-glazing available. Every home is different and has an individual style. Moreover, each one has a different number of windows of varying sizes. Therefore, it makes sense that an article such as this one can only give approximate price generalisations.
Suppose you want an exact estimate for double-glazing your house. In that case, you must contact a local double-glazing fitter. You’ll then receive a more accurate quotation after a site visit.
For now, the information given in the following table can be used as a double-glazed windows cost calculator. Compare your house against our information, and you’ll see how it compares with the cost of many average window sizes and types.
| Property size | Windows | Cost |
|---|---|---|
| 1-2 bed flat (4-windows) | uPVC | £2000 to £2300 |
| Aluminium | £2200 to £2600 | |
| Wood | £3000 to £3700 | |
| 3-bed terraced (8-windows) | uPVC | £4200 to £4600 |
| Aluminium | £4600 to £5000 | |
| Wood | £7000 to £7500 | |
| 4-bed semi-detached (10-windows) | uPVC | £6500 to £7000 |
| Aluminium | £7000 to £7500 | |
| Wood | £10500 to £11500 | |
| 5-bed detached (15-windows) | uPVC | £8500 to £9000 |
| Aluminium | £9500 to £10500 | |
| Wood | £14000 to £15000 |
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Double Glazing Price Factors
We know that each house is different, and these differences, among others, change the price to install your double-glazing. Let’s consider some of these now, and see how they alter the price.
Style
Usually, the style of window you choose varies the price of your double-glazed units. You can choose from casement windows, which have two or more hinges on one of the sides. These are usually the cheapest style you can buy.
Alternatively, you have ‘sliding-sash windows’ to choose from. Sometimes, these are known as ‘box-sash windows’. Originally, the frame had a vertical box on each side containing a lead or cast iron counterweight. The vertically sliding–sash would then be connected to the weight using a rope over a pulley. These days, strong springs counterbalance the sash’s weight, so they no longer need the boxes. Sliding–sash windows are about twice the price of casement windows. A typical 1.2m x 1.2m sliding sash window, excluding installation, costs around £800.
Double-glazed bay windows consist of a combination of opening, and closed windows, protruding from the wall. Their frames connect either at right angles (in the case of bay windows) or at other obtuse angles (as with bow windows). The bow window layout involves wedge–shaped joining pieces, strong enough to carry the load of the window’s ‘mini roof’. It also needs skilled double glazing installers able to work from precise construction drawings. A typical 3m x 1.2m, 3-section bow window costs around £1200 (excluding installation).
Number of windows
How does the number of windows affect a quotation? Sometimes, if you buy more, you can purchase them for less than if you added the single prices together. The reason is that you’re buying in bulk and a manufacturer can afford to sell them cheaper as a ‘job lot’ rather than singly.
Frame size
As you might expect, a larger frame costs more to make because the frame takes up more material. But, the labour costs should be the same because it takes the same amount of time to join two pieces of frame material regardless of its size.
Glass thickness
We also have the price variations brought about by differences in glass thickness. Thicker glass provides better security, a safer environment for kids of all ages, and slightly improves insulation.
Upstairs or downstairs?
Installing a window downstairs is much easier than anywhere else, simply because the installer can stand on the ground, without worrying about climbing up ladders to scaffolding. The added cost of scaffold hire can also work out to be from £60 to £100 extra per window.
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How to fit a double glazed window
The methods used to install uPVC, aluminium and hardwood double-glazed windows have been standardised in recent years. However, there are still variations in fitting methods depending on the manufacturer.
Whereabouts in the country
All labour charges in and around London can be up to 20% more than elsewhere in the country.
Supply only
Suppose you have a local window company or friendly carpenter who can install double-glazed windows. In that case, you can bypass the large specialist companies. Buy the frames ‘supply only’, direct from the manufacturer, and you can make a large saving.
Frame Style & Finishes
There are many types of double-glazed window frames to choose from. But, let’s talk about the different finishes available first.
uPVC
Generally, uPVC costs much less than other window material. Good quality uPVC window frames are easy to maintain. They only require a regular wipe with a damp cloth to remove dirt. If you have a particularly stubborn stain, use a squirt of washing-up liquid in a bowl of warm water. However, not every window frame is made of good quality material. Unfortunately, low–quality uPVC can warp and bend over time, and stain when exposed to UV light.
uPVC isn’t only coloured white. You can buy almost any colour or choose from a range of various wood grain pattern finishes.
Aluminium
Aluminium window frames are usually more expensive than most uPVC frames. You have a long-lasting, durable and strong window frame material in exchange for the higher purchase price. Good quality aluminium frames have better thermal efficiency than uPVC. And, are stronger, so have slimmer cross–sections than both uPVC and timber. They also need far less maintenance than wooden frames.
Aluminium can be coloured using a hot powder dip, to provide a maintenance-free, plastic coating bonded to the metal. The coating provides a large range of colours that last for many years. The colour also looks consistent across your entire window range. Furthermore, the colour can match and complement your home’s décor.
Timber
Although timber window frames are the most expensive of all the options, they give your home more added value than the other frames. They give an elegant finish to your windows. And, if you choose the correct style to complement your property, they can give a classic feel to the overall effect. Timber–framed windows are probably the best type is you have a period property but check with the local authority first. There are various colours and species of wood to choose from, some hardwood and some softwood. If you choose softwood, it’s normal to paint them with good quality external paint. If you choose hardwood, you have the added option of using stain and varnish to enhance the grain.
Unfortunately, although they look great and give a feel of elegance, they also need regular maintenance. But, probably won’t last as long as uPVC and aluminium. So you must decide whether paying the extra for timber is worth it.
Styles
Now let’s look at the styles. We’ve mentioned some of these earlier, but it’s worth going over them in more detail now.
Casement windows
These are the most common style because they’re cheap to make and very versatile. This style is suitable for French doors as well as windows. We can choose windows that don’t open or those hinged at the side, bottom or top. There is a wide range of standard sizes so you can usually find one to suit your window opening.
Sash windows
Also known as ‘box frames’ or ‘sliding–sash’, these are commonly used on Georgian and Victorian period houses. They add a distinctive feel to the property and make it look particularly traditional. Technology has improved since the original timber box frames were invented. So, now springs counterbalance the sliding sashes rather than counterweights. Usually, the opening sashes slide vertically, but they can slide horizontally (without counterweights or springs).
Tilt & turn windows
These are a very modern concept compared to the previous styles. When closed, they look just like any other casement window. But, when opened, they can hinge inwards, or outwards. And, hinged on the side or top. This versatility allows for better ventilation and easier maintenance. They also have a lock feature so they can be opened to allow ventilation, but not enough to create a danger for children.
Bay window
A bay window protrudes out from a flat wall and creates an extra area within the room. Usually, they consist of double windows connected; one half with an opening window and the other half fixed shut. Often, bay windows have interior window seats to make full use of the added views. And, they allow more light than usual to pass into the room. There are many different bay window styles, such as box bay windows, and circle bay windows. But, by far the most popular is the bow window.
Bow window
A bow window is a specific kind of bay window. It isn’t as rigid as the other bay windows and includes angled windows and curved windows, which creates an overall softer feel outside of your home. Bow windows maximise light into the room beyond and give the occupants panoramic views.
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Benefits of Double Glazed Windows
Probably, the most important benefits of double glazing are the warmth, and the savings they give on your energy bills. In turn, this creates a more comfortable home when you can afford to keep your home warm without breaking the bank. Hand in hand with this improvement is that your home has automatically reduced its carbon footprint by burning less fuel for the same amount of heat.
Although not specifically designed for it, double glazing also provides significant sonic insulation. Reduced sound levels make living next to noisy roads or railway lines more comfortable, so you have a better life quality.
Another advantage, tied in with the heat insulation, is the reduced condensation levels you’ll experience as the warm inner glass won’t contact the cold exterior.
If you decide to sell or rent your home in the future, double glazing increases the property’s overall EPC rating. The Energy Performance Certificate contains information about a property’s energy usage and costs. It also gives information on how to reduce energy costs even further. A typical EPC is valid for 10 years.
Double glazing is an investment that might not recoup the money you’ve spent, in terms of the cost of energy saved. But, it gives a more secure and a more comfortable home for your family to live in. It also makes it easier to sell or rent in the future.
Drawbacks
One of the main drawbacks for double glazing is that once the seal between the two panes of glass deteriorates, the glazing panel is useless. There is a special gas trapped between the two glass panes that help insulate the glazing unit without causing condensation. The two glass panes are kept apart with a spacer covered with an airtight seal. The seal degrades over time and allows moist air to enter the cavity. The leak causes condensation and allows heat loss across the cavity.
In the summer months, the glass allows the sun’s UV radiation to enter the house but traps the warmth inside. This situation leads to a stuffy and uncomfortable atmosphere in the room. You can buy double glazing with tinted glass to partially reflect the ultraviolet light, but this option costs extra.
No matter how much manufacturers try to disguise the fact, double glazed windows look new and modern. Therefore, they won’t complement an old or period home very well. Also, if you decide that the cost to replace all the windows simultaneously is too much. And, you choose to buy them one at a time, you have mismatched windows until they are all replaced.
Finally, most double glazing sizes are standard across the industry, so might not fit the window opening in your house, if it’s an old property. Some companies build custom-sized windows, but they cost much more than the standard sizes.
How are they Fitted?
Fitting replacement windows and doors come under the UK Building Regulations. Therefore, you either have to notify the local authority office beforehand to monitor the procedure or use one of the competent person certifications shown here. We recommend you don’t try to install them as a DIY project; it’s not an easy task. Instead, use a professional who is already certified to self check their work.
Whomever you use, it’s useful to know the installation procedures. However, remember that different manufacturers might recommend various methods depending on how they have manufactured their product. Use this list of steps as a guide, but remember that you should always follow the manufacturers’ instructions.
How is the window delivered?
You’ll receive each window in three parts:
- Cill.
- Frame.
- Glass.
You’ll find the glazing beads already clipped into the frame. And, they are easy to remove without the glass in the way. uPVC cover strips come in long lengths from which you can cut to length.
Removal of old window
Remove the old window as carefully as possible. You have to repair any damage to the walls, so the more care you take, the less work you need to do later.
Removing an old window isn’t easy, and the method depends on the design of the old window. So, leave these details up to the professional. Remember that screws hold the frame in place. And, fix through the sides into the wall. So this is where you must start. And, you must try to remove the old frame without breaking any glass.
Therefore use this sequence:
- Remove any opening sashes or casements.
- Cut through the cill or side of the window frame with a saw.
- Lever the cut piece away from the wall using a crowbar.
- Finally, lever the remainder of the frame away from the wall, taking care not to break the glass.
- Make sure you haven’t damaged any damp proof course that might be present. If you have, then replace or repair.
Install cill
- Cut the cill to fit the brickwork opening’s width.
- Glue the plastic endcaps into place on both ends of the cill.
- Sit the cill onto the wall’s outer skin. Ensure it is level using a spirit level. You might need to use plastic spacers to raise certain sections. The spacers should come with the window.
Prepare the frame
- Screw fixing clips onto the frame’s sides, one at about 100mm from the top and one at 100mm from the bottom. Depending on the wall, the clips might point towards the outside or the inside of the room.
- Smear a bead of silicone sealant onto the cill’s upper surface where the frame sits. And, against the small upstand at the back of the cill.
Install frame
- Sit the frame onto the cill, ensuring the silicone sealant seals the joins.
- Check the frame is upright, and square in the opening. Once again, use sliding wedges to adjust the frame.
- Drill into the brickwork, through the holes in the fixing clips.
- Screw the fixing clips onto the brickwork using suitable screws and wall plugs.
Install double-glazing unit
- Lift the double–glazed unit into the frame’s glazing rebate. Use plastic spacers to ensure an even space on all sides.
- Clip glazing beads into place.
Make good and clear up
- Squirt expanding polyurethane building foam around the gap between the frame and the brickwork to seal all the gaps. Wait for the foam to cure before going any further.
- Cut the cured foam flush with the frame and remove the pieces for disposal.
- Either make good with mortar on the outside and plaster on the inside. Or, use uPVC mouldings glued with silicone sealant to cover the cut foam.
- Clean up.
Duration
To remove the old window should take no longer than an hour. Installing the new one should take about 45 minutes, not including making good and waiting for the polyurethane foam to cure.
Building Control, Planning Permission & Accreditations
Planning Permission
We don’t usually need planning permission for replacement double-glazed doors and windows as long as they are of similar appearance to those we intend replacing. However, the council might withdraw permitted development rights for your property. If you live in a Conservation Area, National Park or Area of Outstanding Natural Beauty, you must apply for permission. Similarly, if you live in a listed building, you must apply for ‘Listed Building Consent’ for significant work.
Building Regulations
The UK Building Regulations apply to all replacement door and window glazing, specifically the following Approved Documents:
- Part B – Fire Safety. This section deals with the requirements of preventing fire within a building and the means to escape. Specifically, there must be at least one window capable of providing a means of escape from a burning building.
- Part F – Ventilation. This section deals with a building’s air quality and humidity, and how windows ventilate the space.
- Part K – Protection from falling, collision and impact. This section deals with positioning windows and glass panels in doors, how to prevent collision with them.
- Part L – Conservation of fuel and power. This section deals with the thermal insulation properties of double-glazing.
- Part Q – Security. This section deals with the ways to ensure property remains secure. So windows must have adequate locking systems to prevent unauthorised entry.
- Regulation 7 – Materials and workmanship. This regulation ensures that all materials are of adequate quality. Furthermore, the quality of workmanship for manufacture and installation is suitable to provide a ‘Fit for Purpose’ product.
FENSA
FENSA is a scheme, authorised by the UK Government to ensure compliance of replacement doors and windows with the UK Building Regulations. Manufacturers and Installers have regular assessments to make sure their standards are maintained. As a bonus, FENSA registered installers issue a certificate to prove that the product’s installation complies with the Building Regulations. The installation company also informs the local authority to save you the trouble.
Other accreditations
Other accreditations to look out for include:
- CERTASS, the UK Government approved competent persons scheme. CERTASS registered members can self certify their work and also give you a certificate to prove the standard of work.
- BSI, British Standards Institute certifies that manufactured products meet the government standards for safety and quality.
- GGF, The Glass and Glazing Federation is the industry authority and promotes best practice, encourages better technical standards and monitors health and safety standards.
- SBD, Secured By Design, is the official initiative for security sponsored by the UK police force. The initiative tries to improve the security of buildings. If you see this accreditation, you know that the police recognise the security products.
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Double Glazing Q&A
Is double glazing worth the money?
You should regard double glazing as a long term investment. Although you see savings in your heating bill over the years, it isn’t often that you recoup what you spent out on the window replacements. Regard the project as a way to make your home more secure and more comfortable to live in. You also have far less maintenance to do over the years. Moreover, if you decide to sell or rent your home in the future, it will be far more attractive than a home with single glazing.
How long do double glazed windows last?
Your windows should last from 25 to 30 years. But, if your home is in a sheltered area, not subject to extreme weather and you regularly maintain the windows as the manufacturer recommends, they should last longer.
There are certain tell-tale signs you should look out for that tell you when the windows need replacing:
- Notice draughts around the windows.
- Look for cracks or chips in the glass.
- There might be condensation on the inside of the glazing unit.
- Is there water leaking around the window?
- Your energy bills steadily rise.
- It becomes harder to open and close the windows.
Usually, the sealed units degrade first and cause condensation inside the unit. Good quality glazing unit seals can last for about 30 years or so. But, if the seals last for around 20 years, you have had a good life from them.
Is laminated glass better than double glazing?
That depends what you want out of the window. If you want better security and safety, then use laminated glass as it is very difficult to smash. On the other hand, if you want heat insulation, use double–glazing. After all, that’s how it was designed.
But, if you want to incorporate both, you can. You can buy laminated double–glazed units to combine the advantages of both types. Unfortunately, they cost more too.
Can you fix condensation in double glazing?
Yes, you can. Some companies specialise in reconditioning and repairing double–glazed units. First, they drill a small hole through the spacer bar into the cavity. Then, they inject a desiccant into the cavity to absorb all the moisture. They can also replace the gas between the glass. Finally, they seal the hole to prevent further moisture ingress.
Why can I hear noise through my double glazing?
Double-glazed windows reduce noise, not eradicate it. However, if you hear more noise coming through than usual, it’s time to see if part of the window has failed. You might have problems with the window frame, the rubber seal between the frame and glass, the glass itself, the cavity between both glass panes, or the joint between the frame and the wall.
Suppose your windows are more than 10 years old. In that case, it’s a good possibility that the seals have degraded or that you have a leaking spacer in the double glazed unit itself.
If you can’t see anything obvious, call in a professional double glazing expert to find the problem.
Get Online Double Glazing Quotes
If you believe it’s time to replace your windows for some modern double-glazing, don’t do it without looking at a few different companies first.
Complete the form on this page, and you’ll receive 3 or 4 quotes so you can sensibly compare the double– glazed window costs, without choosing the first company you see.
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