Everything you need to know about double glazing

What is double glazing?

First things first. Double glazing is a phrase that’s so ubiquitous in construction and home improvement that it might seem like it needs no introduction. But to really understand its benefits, it’s first important to get a grasp of exactly what it is.

Put simply, double glazing is used in all kinds of glass installations (particularly windows), and involves two panes of glass set in the same frame, that are separated by a thin layer of air (a vacuum) or sometimes inert gas such as argon. It’s this layer between the two panels that’s the magic ingredient.

Double glazing keeps the cold out, and it keeps the warm in. It reduces drafts, and it’s a vast step up from single glazing – which involves a single pane of glass alone acting as a barrier between the inside and outside worlds. As anyone with single glazed windows likely knows, during the cold months, these lone panes can act like chilling units inside a home.

The origins of double glazing

The earliest accounts of glass window panes being doubled up to act as a shield to the cold are a little hazy, but some put the origins as early as 1870, in Scotland. Anyone who’s made a trip up to the highlands will know just how cold Scotland can be, and during the winter, Victorian houses with multiple rooms to heat (and a feeble kitchen fire often the only source of warmth) resembled something more akin to giant fridges than family homes.

Inhabitants of these chilly abodes discovered that by bonding an extra sheet or pane of glass onto their sub-par windows with putty, things got – albeit a little -warmer. These bolstered windows thickened the barrier between the harsh winter chill and the shivering, blue-lipped families within; drafts were reduced and temperatures improved from levels akin to ‘this is like living in an ice age’ to ‘maybe we’ll all make it through the winter this year!’

Double glazing as we know it today, however, was invented in 1930 in the USA, by C D Haven. His maverick designs involved two panes of glass, equal in size and thickness, bonded into one single frame. This required perfect uniformity in the glass used, which was pretty expensive and impractical at the time. It wasn’t until 1941 that he even managed to secure a deal with a company willing to produce his innovative product.

After WWII putting a hold on things, Haven’s ‘Thermopane’ product was finally put into production in 1952. It promptly became one of the most popular luxury products on the home market.

In the UK, double glazing didn’t take off until the 1970s, when skyrocketing energy prices (as a result of the country trying to reduce its dependence on foreign oil supplies) led homeowners to seek alternative ways to reduce their energy costs, and improve the efficiency of their homes – and double glazing offered an effective solution.

What does double glazing do?

So, with a knowledge of both what double glazing is, and where it came from, the next logical question is what does double glazing actually do? Aside from things like electronically automated windows and doors, double glazing offers a range of passive benefits to a property.

Reduces heat loss and drafts

The biggest benefit that double glazing offers, and the thing for which it was originally conceived, is to reduce heat loss in an interior space. Double glazing prevents as much heat from escaping a property, and limits the amount of draft that can enter through the seams. (more details on this shortly).

Provides acoustic insulation

Double glazing also provides effective acoustic insulation when compared with single glazing, as the amount of sound that can enter through a double glazed installation is reduced by the additional material, and the vacuum between the two panels. When sound waves hits a surface, some bounce off, some are absorbed, and some pass through the material. The extra materials used (and the empty space between them) provide a multitude of buffers, which in plain terms, makes a house quieter.

Increases security

Single glazed panels aren’t as effective as double at keeping out intruders, even when they use laminated or toughened glass (explained under ‘types of double glazing’ later). The simple presence of two panes of glass set in the same frame provide, quite literally, an extra layer of security to a property.

Reduces build up of condensation

Condensation forms on surfaces that are cooler than the surrounding air (which is why windows in a car steam up on a cold day – the window is cold, but inside of the car is warm). The heat loss reduction in a double glazed panel means that the interior pane glass doesn’t get as cold, which means condensation doesn’t build up. This in turn can help reduce the moisture inside a property, helping to prevent problems like mould, or laundry that takes forever to dry.

How do double glazed windows reduce heat loss?

Despite these multiple benefits that double glazing offers, almost all home or property owners choose to either upgrade due to the reduction in heat loss it offers. This is usually because reduced heat loss means less need for additional heating, ergo, less money sent on expensive heating bills. So how does this work?

Double glazing reduces heat loss by limiting how much heat can escape a property through both conduction and convection.

Conduction involves heat being transferred through a material: heat hits the glass, and is then transferred through the panel to the outside world – in the case of single glazing, heat hits the panel, and is then passed fairly effectively to the outdoors, effectively sucking the warmth

Double glazing house comparison heat map from your home. Double glazing works against this process, because the conducted heat doesn’t just head outside, it is transferred to the air between the panels – which is where convection comes in.

Convection occurs when heat is transferred through a moving liquid or a gas – in this case, air, or sometimes argon. Air is a poor conductor of heat, so the vacuum in double glazing acts as a blockade, preventing the conducted heat from convecting.

In tackling both of these processes simultaneously, double glazing works to eliminate heat transfer. It isn’t 100% effective by any means, but the differences between single and double glazed homes are fairly noticeable.

Types of double glazing

Broadly speaking, double glazing doesn’t come in a wide range of ‘types’ – all installations work in fundamentally the same way – but the materials used for the frame, and the types of glass employed, do vary. UpVC (or ‘unplasticized polyvinyl chloride’ – good luck saying that after a few ales) is most commonly associated with double glazed windows – largely due to it being cheap to produce, and the fact that it’s relatively durable and recyclable – but other options do exist.

Frames can also be constructed in aluminium, and wood, and advances in modern technology mean that not only can these now be massive in size, but they can also work equally as effectively as UpVC, both visually and practically speaking.

When it comes to the glass itself, a few options are available, which include:

Low E Glass:

This stands for low emissivity glass. This involves a thin metal ‘low e’ coating being applies to one side of the pane, to create an insulating effect. This in turn restricts the amount of heat transfer between either side of the glass, and increases the installations’ energy efficiency.

Float glass:

Float glass is the term applied to the technique used to produce the majority of modern glass for windows and other installations. Developed by Sir Alastair Pilkington, the method involves floating molten glass on a layer of molten metal, which produces a uniform, perfectly flat finish. Float glass might sound fancy, but in fact it’s just the way most glass is made.

Laminated glass:

Double glazing is inherently more secure than single (more on that later), but laminated glass ups that level of security even further. Laminated glass panels are made from two sheets of glass that are bonded together, which results in the pane holding itself together if it breaks, rather than exploding into a million tiny pieces. Speaking of which:

Toughened glass:

Toughened glass is, as it name might suggest, glass that has been strengthened – using heating tempering processes – to ensure that in the unfortunate event it breaks, the pane crumbles into small chunks, rather than razor sharp shards. This type of glass has become standard in everything from car windscreens to telephone boxes, and double glazing that uses toughened glass provides a vastly safer and more secure option.

While this is far from an exhaustive list, what we hope it highlights is that double glazing in and of itself isn’t an out-of-the-box product, it’s a technique, and the result of a specific manufacturing method. This is partially why, when it was introduced, double glazing was (and to an extent still is) misunderstood, as those flogging ‘double glazing’ gave the impression that it was almost like a brand, when in reality the scope for different designs is vast.

How efficient is double glazing?

With an understanding of how double glazing works to prevent heat loss, the real question on the lips of many bill-conscious homeowner is how effective is it, and how much money would it save you?

Naturally this is assuming the primary intention for a potential upgrade is to cut heating bills, but issues of security or acoustic insulation are a little more subjective and difficult to measure. But some research indicates that double glazing can cut noise levels by anything from a small few, to 35 decibels – about the level of a normal conversation (particularly poignant if you suffer from chatty people outside your home).

When it comes to heat loss however, there are a few more numbers to go by. Firstly, the amount of money you stand to save, and the amount of energy you’ll be able to hold off from using, will depend largely on the size of your property, and how much energy you usually use.

These statistics offer a useful insight as a guide. The findings, from Confusedaboutenergy.co.uk, paint an illuminating picture, about how the effectiveness of double glazing can vary dramatically.

A 3 bedroom gas heated house, using an average of 15000 kwh of energy per year, saving around 10% of their energy costs through the insulative powers of double glazing alone, stands to save around £70 a year. Thus, if the upgrade to double glazing cost them £5000, they would be able to pay it back… in about 70 years. Not exactly time efficient.

However, a slightly larger home using electricity as the primary source of heating, burning through an average 20,000 kwh per year, would be able to pay back a similar upgrade in just over 16 years.

So is double glazing worth it?

The ultimate question of whether double glazing is ‘worth it’ will depend largely on how much money you stand to save in your heating bills, weighed against the cost of upgrading your glass installations from single to double glazed. Using the figures mentioned above as a guide, this will depend on your own property situation – but in most cases, it will be many years before the glazing ‘pays for itself’.

However, with house prices rising in the UK, more people are turning to home improvement rather than upgrading to a more expensive, larger property. The sheer difference in cost between 3 and 4 bedroom houses (see image) alone is enough to justify why so many are making this choice.

If this is the case, then often double glazing is entirely worth the additional expenditure. If you’re planning to add entirely new glass installations such as windows and doors to your home anyway – particularly if you’re creating an entirely new space which will require heating too – then opting for double glazing can save a lot of money in the long run.

If you’re in a position where money isn’t as much of a concern, and you’re purely considering double glazing as a practical option, then it’s almost always the best choice. The added heat loss reduction and acoustic insulation it provides improve the quality of interior spaces immensely.

If this applies to you, it’s also worth mentioning that double glazing isn’t where the buck stops when it comes to the best insulative glass options. Technology moves fast, and triple glazing is now a viable option on everything from small windows to large panels. With options including triple glazed glass doors available, if you’re looking for the very best insulative solution on the market, double glazing may no longer be the best choice for you.

A window of opportunity

So, there you have it. Everything you need to know about double glazing (we hope.) Double glazing is becoming, and in fact has become, the standard offering for glass upgrades in most homes around the country, and indeed the world. It offers plenty of additional benefits, making a home warmer, quieter, and more energy efficient.

Granted, these perks alone may not be enough to justify a full upgrade of all of your existing single glazed windows, but if you’re planning on extending your property or including a new glass installation, then when it comes to double glazing – the case is clear.

And with that terrible pun out of the way, if you have any additional question about glass, glazing, or how Cantifix could help you transform your home or property, please don’t hesitate to get in touch!