wind turbines

Window Energy Ratings: Explained

When it comes to windows, energy efficiency is super-important.  Any window which effectively excludes cold air, while slowing the release of heat into the outside world, will pay for itself in the long run.  On the other hand, a window which allows heat to bleed from your property will do the opposite – placing a drain on your hard-earned cash, and negating any short-term saving you might have made by opting for a cheaper window.

Clearly, there’s a cost-benefit analysis to be made.  All other things being equal, you’ll want a window which returns the best possible efficiency for the lowest possible cost.  But there’s a potential for difficulty, here: how are we to know which windows are the most efficient?  There are several different measures, but of these, perhaps the simplest to get your head around is the rating value.

What is the energy rating?

On modern windows (and many electrical appliances) you’ll find a chart with a series of coloured bars on it.  At the top of the chart is the ‘A+’ rating, which indicates the most efficient type of window commonly available.  At the bottom of the chart is the ‘G’ rating, which indicates the worst.

energy ratings

These colour-coded charts are a relatively recent development.  Window Energy Ratings, or WERs, first came to be in 2004 thanks to the British Fenestration Ratings Council, which was taken over by another organisation named the Glass and Glazing Federation, in 2006.  The scheme, since 2010, has also been administered by another company:  the thermal ratings register.

Unlike other measures of window efficiency, like the ‘u’, ‘l’, and ‘g’ values, WERs measure the effectiveness of the window as a whole, rather than an arbitrarily-defined part of it.  It examines several elements:

  • The amount of heat that can pass through the window from sources other than sunlight, or the ‘u-value’
  • The window’s air-permeability, or ‘l’ value.
  • The amount of heat gained by sunlight, or the ‘g’ value.
  • The overall energy rating of the window, which combines the three above factors into a single figure.

Your choice of window should take into account each of these factors, as well as the place you intend to install the window.  If you’re installing windows into a house in the UK, where sunlight comes from the south, then the ‘g’-value of a window will be less important on a north-facing window than it might be on a south-facing one – since the former isn’t going to receive any sunlight.

In conclusion

Ideally, you’ll want a window that’s as efficient as possible.  Modern double-glazing can achieve u-values in of just over 1.2W/m2K – and this is a good ballpark to aim for.  If you’re willing to install triple-glazing, then you might go even lower.  It’s worth noting that these figures only account of the raw performance of the window when it’s new – by maintaining your windows correctly, and drawing heavy curtains over them during night-time, even greater efficiencies can be obtained.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

roof window

What’s the Difference Between Roof Windows, Skylights and Light Tunnels?

Roof window, skylights and light tunnels are all types of windows that are fitted into the roof of a home. They all look great and let plenty of light into the room, but despite serving a similar purpose, they each have some key differences.

Roof Windows

A roof window is a type of window that’s fixed into your roof, oddly enough.  It’s different from the other varieties featured here in large part because it has the ability to open and close.  Roof windows tend to be designed to allow the occupant of the room to see out in the surrounding area, and they tend to be built into the side of angled roofs.



A skylight, by contrast, is a window that’s positioned very high up, far out of reach.  They’re usually not designed to be opened, and are intended to allow light in rather than provide a view out.  That said, some models can be opened, usually via a remote control device.

Light Tunnels

A light tunnel is something completely different.  It’s a long tube, the interior of which is covered in a reflective coating.  This tube leads from the roof of a building down into a hole in the ceiling.  At the top, you’ll likely find a transparent dome which is designed to catch as much sunlight as possible and pass it downward.  At the bottom of the tunnel you’ll find a frosted plastic or glass disc called a diffuser – which is designed to ensure that the sunlight being ferried down into the room spreads over as large a space as possible.  Light tunnels will have the lowest impact on the exterior of a home – though some examples can work with a traditional window rather than a dome.

Which are best?

If you’d like to introduce a little extra light into your interior space, then any of the devices we’ve looked at will provide it, but some will make a better fit for your space than others.  If you’ve converted your loft, and have an angled wall available, fitting it with a large roof window will provide you with a view over the surrounding area.  If you’ve got a high ceiling which no-one can reach, installing a fixed skylight might be just what’s required to brighten the area up.  For areas into which it’s difficult to get natural light by any other means, and where privacy might be desired, a light-tunnel might work well – a toilet or bathroom being among the best examples.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

casement window

Types of Windows: Explained

Traditionally, most windows were hung and opened using a side hinge or a sash. While these are still very popular, new technologies mean that modern windows come in several different varieties.  Let’s take a look at some of them.

Sash Window

Sash windows were especially popular during the Victorian era, so look great on homes from that period.  They consist of a single fixed panel, and one (or more) mobile ones.  These panels are slightly offset from one another, and are able to slide alongside one another in special grooves.  The classic format of a sash window is to have two panels in a vertical arrangement, each housing a three-by-two grid of rectangular panes.  Sash windows overwhelmingly tend to open from the bottom-up, but it is possible to install a sash window which opens sideways.

The major disadvantage of a sash window is that it’s impossible to open one entirely – you’ll instead fold half of the window behind the other half.  With the help of additional panels, you’ll be able to collapse the window even further – to a third or even a quarter of its normal size.  Such designs, however, are rare and difficult to implement.

Casement Window

A casement window (pictured above) is attached to its frame via a set of hinges which run along one side of the window.  They were among the first windows to be common in the UK, being popular before the spread of sash-based windows in the 19th century.  They’ve now returned to the front of the pack, so to speak, and are ubiquitous in new builds across the country.  Depending on their design, casement windows can be opened with a lever or a handle – which is normally positioned on the side or bottom of the window.  Casement windows invariably open outwards, so they’re unsuitable for spaces where there’s an object obstructing the path of the window.

awning windowAwning Window

An awning window is functionally the same as a casement window, except that it opens from the bottom rather than the side.  They’re great for airing a room when it’s raining, since all the water will hit the sloping glass and drain away.  You’ll find this sort of window on many angled roofs, where drainage away from the aperture is essential.

Hopper Window

A ‘hopper’ style window is another variety of casement window, whose hinge is at the bottom rather than the top.  They tend to be rarer, since it’s physically easier to open a window from the bottom as it tends to be more accessible.  Certain circumstances, however, might call for a hopper window – particularly in larger upstairs windows whose top is around head height.

Skylight Window

A skylight is a window that goes into a ceiling.  In contrast with other sorts of roof windows, these tend to be out of reach; their purpose is to allow natural light in rather than providing a view.  Skylights are not designed to ever be opened.

Shaped Window

While the sorts of windows we’ve discussed are tried-and-tested, it’s sometimes a good idea to try something a little bit different. A bespoke window of an unusual shape might be just the thing to add a little bit of visual interest to a property.  If you’re planning an extension, or just an extensive redesign of an existing part of your property, the right made-for-purpose window is sure to make an excellent visual centrepiece.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

listed building

What is Secondary Glazing?

Not all homes – namely those that have “listed” status – are able to reap the benefits of double glazing.  In such cases, alternatives must be sought.  One such alternative is what’s called “secondary glazing”.  Let’s examine this technology – and see why your home might benefit from it.

What’s the problem with double glazing?

Double glazing works by sandwiching an empty space between two panes of glass.  This prevents the flow of heat and sound from one side of the window to the other – as vibrations in one pane won’t be conducted immediately to the other.  In double glazing, the entire arrangement is housed in the same window – so you won’t deal with the panes separately, but instead as though the device is one unit.

As window technology has advanced, manufacturers have resorted to ever-more ingenious means of achieving the required performance.  Among these is the practice of placing an inert gas between the two layers of glass.  Heat finds it even more difficult to pass through such things, and so a more efficient window is thereby created.

While this is undoubtedly a welcome development that’s saved an enormous amount of energy over the years, it is one with an unfortunate side effect.  Because the interior of the window is completely air-tight, there is a pressure difference between the air (or lack of it) on the inside of the window and the outside.  This causes the glass to become slightly bowed – an effect which can be observed from the outside of the property.

In period homes in conservation areas, this presents a particular problem.  A Georgian property with an otherwise authentic appearance is likely to be undermined if its windows are recognisably modern.  Planning permission for such changes, then, is unlikely to be granted.

How is secondary glazing different?

Secondary glazing works by augmenting an existing window, rather than replacing it.  It consists of an extra panel that is placed on the inside of the window, attaching to the frame.  It’ll go a long way toward excluding any pesky draughts, as well as reducing noise and heat-retention in much the same way that double glazing does (albeit not as effectively).  If you’re the owner of a period property, it’s an obvious choice.

One other advantage that can be yielded from secondary glazing is that it’s able to be easily removed when it’s not needed.  During the summer, you might find that a window (usually a south-facing one) is receiving lots sunlight, and that you’d like to let it through.

Older properties can sometimes be difficult to maintain.  A set of secondary glazing is sure to help reduce those winter heating bills without compromising the look of the property – and it’ll do a great deal more besides, too!

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.


How to Draught-Proof Windows

Anyone who’s ever tried to curl up in front of the television, only to find a persistent and elusive gust of cold air is coming from somewhere, will understand how annoying draughts can be. However, draughts aren’t bad simply because they make us uncomfortable. They can also escalate the home’s running costs as we crank up the heating to compensate for the cold air.

Which windows suffer from draughts?

Modern double and triple-glazed windows should not require draught-proofing. If they do, there’s a problem.

If you’re the owner of an older, listed property however, you might not be able to obtain the necessary planning permission to make the switch to double or triple-glazing.  Fortunately, there are ways of repairing the damage caused by draughts, and slowing – if not halting – their development.

Where is the draught coming from?

In order to locate your draught, you’ll need nothing more advanced than a candle – just run the flame around the edges of a window you suspect to be draughty.  When the flame moves, it means that it’s being pushed around by incoming air.  If you’d like to do this more easily, or you have a lot of windows you’d like to check for draughts, you might consider an electronic draught-detector – these are a special sort of thermometer which works like a barcode scanner – run it around the edge of your window, and when there’s a sharp drop in temperature, it’ll let you know.

What can I do to get rid of the draught?

Once you’ve located the draught, you’ll be able to do something about it.  This something usually comes in the form of a replacement compression seal.  These rubber strips are designed to grip the side of the window, and will compress under pressure.  You’ll need to cut yours to size and glue it to the window frame – following which, it’ll form a tight seal whenever you close your window.

Such seals aren’t appropriate for sliding sash windows, as they’re designed to be squashed rather than rubbed against.  Instead, you’ll want to use brush-strips.  These will sit alongside the interior of your window, and allow them to slide against them bristles, which will still help exclude the majority of the draught while ensuring the window can still be opened.

Gunned silicone

If you’re looking for a cheap and easy way to fill a pesky gap, then a gun of silicone sealant will probably work.  Simply point the nozzle at the area where you need a draught excluded, and fill it with sealant.  Then close the window in order to create a tight seal.  It’s important you cover the part of the window that comes into contact with a special release agent in order to prevent it from sticking before the sealant sets.  Gunned silicone is undoubtedly an effective solution, but it’s one that relies on the right technique.  If you know what you’re doing, however, it can work very well.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

houses in Svalbard

How the Direction Of Your Home Affects the Windows You Should Choose

Your choice of window can have a profound impact on the way your home looks, and its energy efficiency, but the benefits of a double (or triple) glazed window depend on where they’re positioned.  The reason why is simple:  sunlight doesn’t come from every direction at the same time, but from wherever the sun might be in the sky.

Failing to account for this when you choose your windows is likely to mean wasted energy.  Let’s therefore examine how the position of your house might influence the type of windows you choose.

North-facing windows

Since we in Britain live in the northern hemisphere, we experience our sunlight from a southerly direction.  Consequently, south-facing windows are exposed to sunlight for much of the day.  North-facing ones, by contrast, are in near-constant shade.

In order to see what this might mean, let’s consider why triple-glazed windows aren’t as popular in Surrey as they are in, say, Svalbard (pictured above – a Norwegian archipelago in the Arctic Ocean).  This reason why is simple: the more panes of glass that you stack atop one another, the more you’ll slow the spread of heat (and light) from one side to the other.  This will keep heat inside your home, but it’ll also prevent sunlight from heating up your home as effectively.  If the window isn’t exposed to direct sunlight, however, this won’t be a problem you need to consider – which makes triple-glazed windows more useful in colder climates, and worth the added cost.

South-facing windows

When it comes to south-facing windows in cooler climates (and we’re including the UK in this), the opposite applies – we want to allow the maximum amount of heat that strikes the window to pass through into the house.  This means using low-emissivity glass.

This sort of glass is covered in an extremely thin coating of metal, designed to act as a filter.  It will block ultraviolet light (whose rays have a wavelength of around 300-400 nanometres) while allowing everything else through.  Visible light and infra-red rays which heat up your house will enter virtually unobstructed – and then they’ll be trapped by a similar coating on the other side.

Other factors to consider

Of course, deciding on which windows to buy isn’t simply a matter of whipping out a compass and determining which direction your house faces.  For one thing, not all houses are arranged perfectly parallel to the equator; most of them are at an angle so that no side can really be said to be north-or-south facing.  This will undermine the benefit of a given sort of window technology.

That said, choosing a window that’s appropriate for the position of your house can help yield the maximum possible efficiency saving and is therefore stilll something worth considering.

Looking for new windows for your home? Browse our sliding sash or casement windows or find out about our handmade bespoke windows.

broken glass

Glass as Strong as Steel?

If you take a stroll around a modern city, you’re likely to encounter one material in abundance – glass. It’s this transparent wonder-material that so characterises the cloud-bothering skyscrapers now found in every major city, and whose influence can be found everywhere from smartphones to cars.

Over the years, the process through which glass is made has evolved considerably. The enormous plate-glass windows you’ll find in modern office buildings, airports and shopping centres are a far cry from the panes that were in used in the Napoleonic era.

The importance of alumina

In recent years, one especially promising advance has come about thanks to Japanese efforts to increase the amount of alumina in the mixture. This material is an aluminium oxide, and it’s responsible for giving glass much of its strength. It’s thought by increasing its concentration, stronger glass would result.

This isn’t a new suggestion (in fact, ‘transparent aluminium’ is yet another technology that’s been predicted by Star Trek) but previous attempts to create it have run into trouble. Under normal glassmaking conditions, high levels of alumina would crystallise, rendering the glass distinctly opaque.

A new technique sees the glass levitated above the container while it’s being created. It’s floated atop gaseous oxygen before being melted with CO2 lasers. The result is a material that’s transparent, and comprised of 50% aluminium.

Currently, the new material (whose chemical formula is ‘54Al2O3-46Ta2O5’) has only been created in very small quantities. But those droplets have displayed remarkable properties – being elastic and resistant to scratches and heat. These properties combined have led to it being dubbed ‘the glass that’s as strong as steel’.

Reasons to be sceptical

Of course, describing something as ‘strong as steel’ is pretty meaningless – as ‘strength’ is measured in several different respects. A sheet of ordinary glass might be able to withstand huge amounts of compression pressure – but try to bend it in half and it will shatter into smithereens.

In spite of the understandable hype behind this development, it’s worth considering the materials necessary to create the glass. While aluminium might be widespread and relatively easily obtained (to say nothing of oxygen and carbon dioxide) the same cannot be said of tantalum, which is extremely rare. Moreover, the techniques required to create glass of this sort in large quantities will need a great deal of refinement before they can be considered commercially viable.

We should therefore expect this material to first find its way into places where we need a small amount of high-quality glass, rather than in windows and other larger-scale items. Apple have already experimented with wafer-thin, sapphire screens that’ll resist scratches, and materials like transparent aluminium are surely going to prove attractive.  If past behaviour is any indication, the smartphone industry will likely use this new technology not to make stronger devices, but to make thinner and lighter ones which retaining the same level of strength.