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Double Glazing


Double Glazing UK: The ultimate Guide

Your Questions answered: Our Ultimate Guide to Double Glazing UK.

Double Glazing UKLet’s start our ultimate guide with the answer to the most basic question: “what is double glazing?”.

Initially, it was just a matter of fitting an extra pane of glass to the inside of an existing window frame. These days, secondary double glazing as it became to be known, is far less popular than it was, being overtaken by the modern sealed unit.

The modern sealed unit is made from 2 panes of glass separated by an air gap. Effectively becoming a glass & air “sandwich”, where the air-gap is the “filling”.

The distance that separates the 2 panes can vary from 6 to 20mm, with a larger gap being a more effective insulator than the smaller version.

The gap between the panes of glass creates an insulating barrier to both sound and heat transfer. This barrier reduces the transfer of heat or cold from one side of the window to the other.

So How Much Does Double Glazing Cost?

There are, as you may already have guessed, a number of things that will have an influence on the eventual price of your replacement windows, such as:

  • How many windows will you want to have replaced?
  • The style of the windows you chose (Casement, French, Sash etc.).
  • The window dimensions – height, width, thickness.
  • How many of the windows will need to be able to open & close?
  • What material do you prefer to have them made from (UPVC, Timber, Aluminium)?
  • The window energy efficiency rating (WER) of the units (A++ rated cost more).

Because each job is going to be different, this will reflect in the actual final cost of double glazing your property.

Quick double glazing price guide

A casement window in UPVC sized 100 x 100cm might be priced from £300. If you increase the size to 120 x 120cm, the average cost of a double glazed window can rise to around £400.

  • For a larger order, maybe 4 or 5 widows, if you stick with uPVC and use B-rated units then average costs can run from £1,500 to £2,000.
  • On the other hand, for a larger property like a 3 or 4 bed semi with 10 to 12 windows, the lowest starting cost of replacement windows is generally between £4,900 and £6,000.

You do need to bear in mind that, just by changing the sizes and specifications a little, prices can vary a lot.

Not only that, but prices can vary based on who you are dealing with. For example, a large regional company (even one with a very good reputation) can have bigger overheads and have that reflected in higher prices.

Average Double Glazing Prices for White UPVC Casement Windows

Property TypeAverage Number of Windows Price Guides
Flat4-5£1,500 to £2,800
Small house8-9£3,500 to £5,000
Medium-sized house10-12£5,000 to £8,000
Large house15-18£7,000 to £12,000
Get Free Quotes From Local Suppliers

How to get the best double glazing deals?

Where you are spending a decent chunk of your hard earned savings, it’s always going to pay dividends to shop around. Firstly, you will get a better idea of what the market has to offer and be better able to spot prices that are higher than they should be.

Secondly, having proper quotes from competing installers puts you in a stronger position to be able to negotiate a really good deal for yourself.

What do you get for your money?

In other words, what are the benefits of buying new double glazing windows?

There is a lot of truth in the old saying “you get what you pay for”. If your sole goal is to find the cheapest double glazed windows in the market, then its highly likely that you will just be storing up future trouble and expense.

On the other hand, that doesn’t mean to say that the most expensive replacement windows are automatically going to be the best.

Getting the best value for money in line with your budget is usually the best way to go.

What are the benefits of Double Glazing?

Saving money, improved appearance & security

The number 1 benefit surely has to be the long term savings that can be made on your energy bills.

  • According to a Which.co.uk survey, 44% of those surveyed bought double glazing solely to reduce their energy bills.
  • OFGEM reported the average dual fuel variable tariff as of April 2019 is £104.50 per month, or £1,254 a year.
  • The Energy Saving Trust reckons, for a detached house, you save around £110 to £115 yearly. With good quality double glazed windows lasting for 20 years or more and the cost of energy rising faster than inflation, the amount of money saved over the lifespan of the window will run into £1,000’s.

Try out this calculator for yourself: https://www.myglazing.com/ggf-energy-savings-calculator/

Two other major benefits are, firstly, the improved appearance which in itself will add appeal and potential resale value. Secondly, modern double glazed windows feature multi-point locks and internal glazing beads which improves security. Also, having 2 panes of glass makes them quite difficult to break accidentally.

Windows and Frames: What are your options?

Windows Specification

It’s widely accepted in the industry that the wider the gap between the inner and outer panes of glass, the more efficient the insulation. This is, however only correct up to a certain point.

Double glazing gets its’ “insulating power” primarily by keeping the air within the gap very still. If the gap between the panes becomes too large it encourages circulation within the sealed unit. Circulating currents within the sealed unit will ruin the insulating properties of the double glazing.

Currently, the widest gap used is 20 millimetres. With the panes of glass each being 4 millimetres thick, this gives an overall thickness of 28 (gaps go up in 2 millimetres increments from 6 to 20).

You can replace the air inside the double glazing with an inert gas. Argon is the most widely used at the moment, but you could opt for Krypton or an even denser gas called Xenon. Both Krypton & Xenon are more expensive to use than Argon. If you are going for gas filled units, then the quality of the seals is exceptionally important to prevent the leakage of any gas.

“Solar Glass” is another way to improve efficiency. With this feature, a microscopic layer of metal oxide is applied to the glass. Most often referred to as Low Emissivity or Low-E glazing.

Double Glazing Vs Triple Glazing

Triple glazing is an option that can certainly increase energy savings & security. However, it also comes at an increased cost. This cost is not always offset by the increase in potential long term savings when compared to an A++ rated double glazed window.

Frame Specification

The material used in the frames can make a big difference in both the overall cost of your double glazing and the visual impact on your home.

Two of the most popular materials in use are UPVC and Aluminium.

Of the two, aluminium comes at a higher price, but many feel the aesthetics are much better than those of UPVC. You only have to take a quick look at some of the designs to see how the increased structural strength of aluminium allows for much more slender frames and “contemporary’ designs.

UPVC windows have come a long way since they first appeared. They don’t discolour like they used to, last a very long time and manufacturers have come up with ingenious ways to add colours and even recreate timber grain textured surfaces.

You may want to look at these articles to learn more:

Which are the best double glazed windows?

What is the best design?

It’s often quoted that “beauty is in the eye of the beholder”. What that really means is the best double glazed window for you is not necessarily the best one for someone else.

For some cases, you may actually be limited to a certain style by means of a local planning restriction (listed building or other reason). Other times, it may be that the predominant style of windows in your neighbourhood means you need to “fit in”.

In any event, you are going to find that there are only really about 4 main styles of double glazing windows, and the rest are just variations on those that follow:

  1. Casement windows: One of the most common designs. They are either fixed or open from the side.
  2. French Windows: A pair of windows sat side by side that open outwards
  3. Sash windows: Vertical sliding windows.
  4. Tilt & Turn: This design allows for the window to open inwards from side hinges and/or tilt into the room from hinges at the bottom of the frame.
  5. Bay & Bow Windows: Curved or rectangular, projecting from the property.

You can read more about each design here.

What is the best double glazed window frame material?

Again, the answer to what is the best double glazed window material is going to be largely subjective. In most cases it’s just going to be a matter of personal choice, budget or local planning restrictions.

However, if you want low cost double glazing without sacrificing on overall quality, UPVC windows are a good candidate. They look good, are secure, they last a long time and have very competitive prices due to widespread availability in the market.

If you have the budget and are looking to go a bit upmarket (or you just don’t like “plastic windows”), Aluminium windows could be the perfect solution. Available in slimline designs with a selection of over 150 RAL powder coat colours, you are spoilt for choice.


Here are some of questions we most frequently get asked.

Q1 Are gas filled double glazing windows worth the added cost?

A1: If the difference in cost on your quote is significant, then maybe it’s not going to be worth it. Some installers may charge around £12 a square metre for filling with Argon gas. All gas filled units will lose at least 1% per year but that’s not unexpected. But, if you get badly sealed units, then the gas can have leaked out within 3 years or less. This then, would be a waste of money.

You could always try to negotiate for “free gas” as part of the deal.

Q2 How much deposit should I give to the installer for my replacement windows?

 A2: This can be tricky sometimes. It’s understandable for a supplier to want some type of security deposit for the work, especially if it’s for changing several windows.10% or 20% may be acceptable, but if you are being asked for a high proportion of deposit, then it could mean that the installer is using your money to fund the work – not a good sign.

If you work with installers who are accredited by GGF / FENSA / CERTASS/ DGCOS, you will typically be dealing with a trustworthy professional.

Q3 What guarantees will I get?

A3: There are a couple of things you should look out for. Warranties on the work & warranties on the product. Usually the windows themselves will carry a 10-year guarantee. Work warranties that cover the installation vary per installer. Make sure you confirm exactly what is being included and get it in writing.

Once again, if you work with installers who are accredited by GGF / FENSA / CERTASS/ DGCOS, you will typically be dealing with a trustworthy professional.

Q4 Should I buy double glazing from a big company or a local business?

A4: Both options have their potential advantages & disadvantages.With a big company, you can usually expect them to be financially sound and to have the resources to make sure the job gets finished and built properly. All of them will be full members of either CERTASS, FENSA or GGF. However, it’s likely that it’s more expensive for them to do business due to overheads and in some cases those extra costs get covered by a higher price range.

Companies like Anglian, Everest, Safestyle or Weatherseal have been around for decades and, even though many would say they are not cheap, have installed thousands of windows all over the UK to many happy customers.

Local businesses with lower overheads can pass those savings onto consumers. You should check tos make sure they are registered with a trade body like CERTASS or FENSA because replacement windows need to be certified as meeting current building regulations. FENSA & CERTASS members are allowed to certify installations.

With a local business, you are also likely to find more local customers that you can chat to in order to see how they were treated and if the installer is a good one. Take references where you can.

Either way, according to a report by which.co.uk, only just over 1 in 10 people experienced any kind of problem. The most common of which, was typically about paperwork and not the installation itself.

Q5 What about if I want to cancel my order?

A5: Thankfully, there are a lot of consumer rights in the UK, but there are some points to note when it comes to how & where you order your double glazing.

To summarise the situation, there are times when you don’t have the automatic right to cancel.

  • Windows or doors are made to measure specifically for your job.
  • When you sign a contract at the company offices.
  • You discuss the sale at your home with an employee of the business but go to their office at a later date to “sign up”

and times when you do have the automatic right to cancel.

  • If you get a visit at home and either verbally or in writing agree to a contract, you get a 14 day cool off period.
  • If you agree to a contract online or over the phone, you also get 14 days to cool off.

We are not legal advisers, so this is only a rough guide, but you might find this link useful: https://www.which.co.uk/reviews/double-glazing/article/how-to-buy-double-glazing/your-rights-when-buying-double-glazing

Q6 What’s the cheapest double glazing?

A6: Well, that would be secondary double glazing. This method is to just fit a second glazing layer onto the inside of your existing window frame. It’s actually a very good way to drastically reduce noise pollution.

Following secondary double glazing, in terms of cost, would most likely be UPVC windows (if we exclude softwood). At the higher priced end, you will find hardwood and aluminium.

  • A flat, maisonette or a front of house with 4 or 5 UPVC windows can cost £1,500+
  • A house with 6 or 7 can run from £2,000+
  • Detached property with 10 or 12 windows from around £5,000+
  • If you are also installing a door, you should allow anything from £500 and £1,000 depending on material & quality.

Before you go, it’s important to realise that prices shown in this article can’t be 100% accurate. The only guarantee here is that the final cost of double glazing your home will be different from anybody else’s.

Q7 What are glazing beads & why is is better to have them on the inside?

A7: Glazing beads are thin strips around the edges of the glass, that hold the glass into position within the frame. The reasoning behind fitting them to the inside of the unit is so that they cannot be removed by intruders / burglars.  Once you remove the glazing beads you can take the glass out.

Q8 I fitted double glazing with UPVC windows, why do I have condensation?

A8: That’s probably because your house is not getting much ventilation. Quite a lot of moisture can build up in the house during the course of a day and if it has nowhere to go it will condense on any cool surface – glass is very attractive!

To combat condensation, open a window even by a little whilst you are at home. For longer term solutions, you should fit trickle vents to the windows. These are secure air vents that allow for draught free ventilation and can easily be “retro-fitted”.

Q9 What are chambered profiles & why are they important for uPVC & Aluminium Windows?

A9: The frames for UPVC & Aluminium windows are “honeycombed” with chambers for 2 reasons. The 1st is to improve insulation by trapping air thereby reducing heat transfer across the frame. The 2nd reason is to give the frame improved structural strength.

Q10 How do I get quotes to compare double glazing prices?

 A10: That’s super easy, just go to our quotes page and send us a request

compare double glazing prices
John Francis James
John has been around the building industry since he was a child. With a degree in civil engineering, John is a highly valued contributor to our website.