Everything you need to know about windows

 

Buying new windows is an investment, but if you buy the right window you will only have to fit it once.

• Materials

  Modern window materials & new technologies

  Historically, windows were made using timber frames. Steel windows came into use in the early part of the 20th century, followed by aluminium in the post-war period. But as good conductors of heat, metal windows easily let heat escape from a home. uPVC windows were introduced in the 1980s as a more energy efficient type of window, and remain the most popular window material to this day.

  The modern uPVC window has been in development now for over 40 years. During this time, a great deal of effort has gone into creating something that not only looks fantastic, but also performs to the highest security, performance and environmental standards now expected by the EU and UK Governmental regulations.

  Advances in manufacturing technology means that modern windows offer better performance than ever before. Whichever material you choose, your new windows will improve security, strength and energy efficiency.

  Timber windows

  Offers the lowest thermal conductivity. Provides a traditional look, but is the most expensive.

  Timber is the highest performing material in terms of energy efficiency, as it is a natural insulator that absorbs and retains heat. Timber windows are seen to be most attractive, but natural materials such as wood require more looking after to keep them at their best.

  Timber frames can be made from both softwood and hardwood. Softwood is faster growing and more plentiful, so it's cheaper. Hardwood grows slower and is more durable, so tends to be more expensive. Modern timber frames are engineered to be stronger, meaning they will not warp or bow, and can also be treated to resist rot and fungus.

  The added beauty of timber is that it can have a stained or painted finish. It is the only material that can be repainted a different colour at a later date, so personalising the look of your home becomes even easier.

  Make sure you choose sustainably sourced timber windows that are approved by the Forestry Stewardship Council (FSC).

  

  uPVC windows

  Long lasting and low maintenance, offering high performance at affordable prices.

  uPVC is often touted as a miracle material for windows that tick all the boxes for any project. uPVC is a good all-round material that makes smooth and stylish frames which will never rot, flake or rust. uPVC windows are still among the most energy efficient available and, with excellent double glazing, can achieve up to an A+12 Windows Energy Rating.

  uPVC is a popular choice for windows as it offers fantastic value for money. Although, for some, lacks the unique charm of other materials. However, it is now possible to buy uPVC windows designed to emulate traditional timber frames, to such an extent that it can be difficult to tell them apart.

  Historically you could have any window, as long as it was white. Now uPVC frames are available in a range of colours, guaranteed to last a lifetime with extensive guarantees against frame discolouration. Many windows also now contain lead-free uPVC, which is an important environmental and health factor.

  

  Aluminium windows

  Slim frames let the most light in. Stylish exterior is ideal for modern properties.

  Aluminium windows are used in structural glazing and other commercial construction projects due to its strength. In domestic properties, this allows for a much thinner window frame and a larger glass surface area, letting more light into the room.

  As a metal, aluminium is a natural heat conductor, letting heat pass through easily. Aluminium windows feature a thermal barrier in the frames, which reduces heat loss through the frames. In the last 10 years, thermal barrier technology has improved massively, and aluminium windows can now achieve almost the same high energy ratings as uPVC windows.

  Aluminium windows are also extremely weatherproof and low maintenance. Unlike other metals, aluminium does not corrode, so window frames will not rot, flake or rust. A powdered coated finish allows a wide range of colours to be chosen for the frame – including non-metallic options.

  

  Composite windows

  ‘Super windows’ that offer the benefits of many materials combined.

  Composite windows provide the benefits of different materials, to offer the best strength, security, energy efficiency and aesthetics.

  One popular option combines the craftsmanship and detailing of timber windows with the benefits of the uPVC material. Another option is aluminium-clad timber. For a low maintenance and weatherproof window that offers all the charm of a classic wooden window from the inside.

  Which material should I choose for my new windows?

  Deciding on the best window material for your property can be a challenge. The good news is that window engineering has advanced considerably in the last 15, 25 or even 50 years. So much so that you will definitely notice the benefits of upgrading your windows, no matter which frames you choose.

  With improvements in window design, traditional differences between materials are slowly disappearing. uPVC is now virtually indistinguishable from it's timber counterparts. Stylish aluminium frames are on option that look exactly like uPVC windows, only slimmer.

  That being said, some materials still suit some properties better than others:

  Traditional houses

  Houses built before the 20th century would have originally had wooden windows, and still suit these today. Countryside cottages, 1930s semis and Victorian terraces are examples of period properties where timber would be perfectly suited. With sliding sashes or period detailing, modern uPVC windows can sometimes replicate these styles, but for a truly authentic feel, there’s no replacement for timber.

  Why not try timber casement windows with Georgian bars or sliding sash windows?

  Suburban housing

  Properties in housing developments built from the 1960s onwards tend to have white uPVC windows. Although replacements are a great choice to retain this timeless look, they can be customised with a variety of frame colours to add a unique touch. If you’re looking to maximise light in your home, such as in a basement flat, aluminium windows are a sleek alternative.

  Why not try uPVC casement windows with two colour frames, or slimline aluminium windows?

  Modern architectural

  For that stylish ‘Grand Designs’ look, there’s no better choice than aluminium. Used in structural glazing, aluminium is a strong material that can hold larger glass units, increasing the amount of natural light. Aluminium frames are almost ‘flush’, meaning they sit flatter than uPVC frames and have neater lines – ideal for angular designs.

  Why not try aluminium casement windows?

  Of course, these are only suggestions and you can choose almost any type of window for your home. If you need more assistance, ask your advisor for more suggestions tailored to your property.

• Glass

  Window Glass & Glazing Types

  Originally, windows only had one job, and that was to let light into a building. The first windows were made with pieces of crown glass held together by lattice leading. Soon after, the invention of thinner and flatter plate glass led to larger squares of glass held together by wooden glazing bars.

  Float glass was invented in the late 1950s, allowing for the quicker production of large, flawless glass sheets. This helped spur on the development of more advanced glazing. Double glazing became the norm from the 1970s onwards, as energy efficiency, comfort and security became more important to homeowners.

  So how does double glazing work? And why are more panes of glass better?

  Glazing options

  Single glazing

  Does a job, but offers limited sound insulation, security and energy efficiency.

  A surprising number of houses in the UK are still only single glazed. Windows can be one of the greatest sources of heat loss in a home, and one pane of glass is not sufficient to retain heat. Complaints about old single glazed windows include: cold spots near the window, draughty frames, freezing cold house and noise pollution from the outside. All problems that will disappear by upgrading to new double glazing.

  Installing single glazing is still a requirement on occasion where planning or conservation regulations apply. Along with timber frames, single glazing helps a property retain its period look. Another way to improve insulation under these circumstances is to install secondary glazing.

  Double glazing

  The minimum standard for new windows and the most popular choice.

  Double glazing is one of the most effective ways to improve the insulation of a home, creating a warm and comfortable living environment.

  In a double glazed window, two panes of glass are joined by a spacer bar. The gap between the panes traps warm air, slowing the escape of heat from a building. In addition, the best windows introduce an inert gas, such as argon, which further limits the movement of cold air.

  In the UK, all new buildings must include at least C rated double glazed windows as standard, but many companies are offering double glazing that can achieve an A or even A+ rating.

  Triple glazing

  Safer, quieter and warmer windows.

  Triple glazing contains a third pane of glass, creating an extra cavity which traps warm air and reduces heat loss through the sealed unit. Triple glazed windows are better at retaining heat generated within the home, whilst reducing overheating in summer.

  A common misconception about triple glazing is that the improvement in thermal performance is due to the extra pane itself. However, it is more about the types of glass and coatings used, the gas filled sealed unit and the distance between the panes.

  Is triple glazing really any better than double glazing? Ultimately, triple glazing provides next-level heat and sound insulation. It is up to 35% more effective than double glazing for thermal efficiency, and reduces outside noise by up to 35 decibels.

  For some properties, triple glazing isn’t high priority, but it’s recommended for houses next to busy roads, train lines and under flight paths, or in typically colder areas.

  Secondary glazing

  A practical alternative to double glazing for conservation areas
  

  If you live in a listed building or conservation area it may not be possible to replace your windows. In this instance secondary glazing would be the perfect option to reduce noise and cold draughts.

  With Secondary glazing an additional window installed directly inside of the existing frame. It can help your home achieve thermal, security and soundproofing benefits, whilst remaining invisible to the outside.

  

  Types of glass

  It’s not all about the number of panes of glass. New technologies have been developed that make window glass stronger, shatterproof, clearer and quieter. It's important to consider what type of glass would be best suited to your requirements. 

  Low E glass

  Invisible reflective coating

  Low emissivity glass has an invisible, thin coating applied to its surface that reflects heat. It is strategically placed on the inner pane of glass to help keep heat indoors and to maintain a comfortable temperature.

  Low iron glass

  Clearer, allowing for more light

  Windows that contain low iron glass are noticeably clearer. They allow a higher level of light to pass through compared to older glass types, which sometimes have a slightly green tint. 

  Security glass

  Thicker glass, laminated or toughened to enhance security.

  Security glass is available in a range of sizes and thicknesses depending on your security needs. Typically, laminated glass is 6.4mm thick (compared to 4mm for standard glass), and contains a thin plastic interlayer that prevents the glass from smashing. Toughened glass is up to five times as strong as ordinary glass of the same thickness.

  Used as an outer pane in a double glazed unit, this provides an extra level of security to the window as a whole. Toughened glass must also be used for fixed lights in side panels to doors, as well as in windows close to the ground.

  Sound reduction glass

  Outstanding levels of noise reduction

  Sound reduction glass windows contain an inner pane that is 6.4mm thick supported by an outer pane that is an incredible 10mm thick. Together, they provide excellent sound insulation. A thin and lightweight solution to noise problems.

  Coloured glass

  Enhancing the character of your window and home

  Add coloured shapes, patterns and bevelled designs into the glass itself. Decorative glass looks beautiful in top hung fanlights – the top sashes of casement windows – as well as feature windows in halls and stairwells. Coloured glass is similar to stained glass windows, but it doesn’t require leading to hold the glass together.

  Leaded glass

  A new version of an old classic

  Stylish strips of lead are a purely visual benefit that can be added to your window in order to make it more aesthetically pleasing. There are a range of leaded glass options that suit both modern and traditional houses, including square and diamond designs.

  Obscure glass

  Maintains privacy with distinctive character

  Obscure glass creates a ‘cloudy’ effect, enhancing privacy by blurring out your home’s finer details to passers-by. Also known as privacy glass, there’s a variety of textures available, such as leaves and flowers, as well as grainy patterns.

• Design

  Window Styles & Designs

  Window styles tend to be named after the way they function, and although window companies give their ranges different names, they’re usually self-explanatory. Casement windows open outwards, sash windows have sashes that slide up and down, and tilting or turning windows usually open inwards or flip around for ease of cleaning.

  Most people opt for casement windows. These are the simplest to operate and suit nearly every home. However, some houses will require different window designs, depending on the project.

  Casement windows

  Casement windows have emerged as the most popular window style. They can be hinged on the side to open left or right, or hinged to open upwards. Extremely versatile, they can be designed to suit a range of properties, with over 250 frame designs. The modern technology, with multiple locking points along all sides of the frame, makes a casement window extremely secure.  

  

  Dual turn windows

  Dual turn windows  combines the classic  features casement with modern pivot technology. They work by pulling the window down and inwards to open, turning on a pivot to fully reverse the sash. This is useful for cleaning both sides of the window with ease, as well as allowing optimum airflow on a hot summer’s day.

  Tilt and turn windows

  Tilt and turn windows possess a dual hinge design that tilts and open inwards using hinges at the bottom and side. Tidy and efficient, these windows have been designed for flats, apartments and other upper storeys, providing secure ventilation and an easy way to clean the glass inside and out.

  Sash windows

  Amongst the most traditional window styles. Historically made from timber, sash windows can now be made from uPVC, for a classic design that fulfils modern day performance requirements.

  There are several different styles of sash window available, modelled on designs from the Georgian, Victorian and Edwardian periods. Designs vary depending on the era, but tend to have a thicker frame depth and a deep bottom rail.

  Sash windows traditionally operated on a pulley system of cords and weights, allowing users to lift the sliding windows open and shut. Modern sash windows tend to use a metal rod or ‘spiral balance’ to slide the window open. This device is smaller and so allows for a larger glass area, letting more light enter the room.

  Tilt sash window

  Tilt sash windows have the appearance of a standard sash option but as well as sliding, one or both of the sashes tilt inwards for easy cleaning. Offering the same attractive appearance of the traditional sash window, but are more practical for the modern home.

  Georgian windows

  Georgian bars can be added to either casement or sash windows to provide a touch of traditional charm to your property. These bar details can sit internally or externally. Internal glazing bars sit between the glass panes and keep your windows easy to clean, whereas external bars sit on the surface of the glass.

  Another option is diamond or square leaded glass designs – these patterns are applied to the outer pane of double glazed units and are available in many widths and colours.

  Custom shaped windows

  Windows don’t have to be rectangular. Bespoke shaped windows can give your home a unique edge. Every good window company will make your windows to measure. Arched, round, angular and apex windows can be easily custom made. 

  Fixed pane glass windows

  Often referred to as a ‘picture window’, fixed windows do not open. They are installed purely for letting light into a space, or to showcase the outdoors. Fixed pane windows don’t just have to be rectangular. Circular or hexagonal portals are popular, as are lancet and other shaped fixed lights in high or hard-to-reach places.

  How to choose a window style that's right for your home

  Many people decide to replace their existing windows like-for-like, but with so many window designs, frame styles and other decorative features, there is an option to suit your property.

  First, think about the window’s functionality. Standard casement windows are well suited to most projects, but if ventilation, security or maintenance are a concern, it’s worth checking out other styles.

  One way to make sure your house looks top class is to ensure that each individual window appears balanced in its own right. We call this ‘window framing.’ Choosing a symmetrical window will enhance the aesthetics of your property and create a lasting impression.

  Whichever window style you choose, you can complement the look by customising with decorative glass, Georgian bars, and customisable fixtures and fittings.

  Combining window styles

  Houses often incorporate window sets made from different configurations. Many styles can be combined to create a row of windows, such as sash fitted together to create a bay or a bow window constructed with a Georgian design.

  The same applies when choosing windows for a conservatory. It’s possible to design any glazing project that takes your style and requirements into account.

  

• Frames

  Window frames

  It is important to understand what makes a good window. The frames are an important aspect. Not only is the structure paramount, but the materials and finishes too. These all impact on the energy efficiency, security and overall appearance of the window.  

  How are windows made?

  Window frames are constructed by taking long lengths of ‘profile’, cutting them to size, and fixing the ends together to create a rectangle (or other shape!). Different materials are fixed together in different ways – timber windows can be ‘joined’ together with interlocking sections, whereas uPVC and aluminium frames are welded or fused together under high heat.

  Some uPVC and aluminium windows are ‘mechanically joined’ to replicate the same process as a wooden frame, giving a more classic look. Better quality uPVC windows are now made using a ‘smooth welding’ process, resulting in a seamless and more polished finish.

  Timber window frames & joinery

  Timber windows are made by fitting together solid lengths of wood that have been pre-cut and styled by machine or hand. Good quality timber windows are made using engineered wood that has been layered and compressed to increase the structural stability of the frame. Timber is naturally insulating, and the frames don’t require any other materials or parts.

  uPVC window frames & chambers

  You might think that because timber frames are made from solid pieces of wood that they are all created in this way, but it’s not the case. Timber is a naturally insulating material, but uPVC windows work by trapping air in pockets within the frame, reducing thermal conductivity and stopping heat from escaping.

  These are called ‘chambers.’ The more air chambers a window frame has, the more energy efficient the window can be. This is due to the fact that each chamber provides an additional barrier for the heat and the cold to contend with. The outerframe and the sashes can each have a different number of chambers, but numbers can range from a three chambered frame to a highly energy efficient nine chambers.

  

  Aluminium window frames & thermal barriers

  You might have heard that aluminium window frames are ‘cold’ and not as energy efficient as uPVC. With older aluminium windows the profile could only be ‘extruded’ in one piece, meaning window frames used to be made entirely from metal. The worst material for letting the heat escape!

  Over the years, advances in manufacturing led to windows being made in two parts, allowing for a polyamide thermal barrier to disrupt the transfer of heat. Like uPVC windows, aluminium frames also contain energy efficient chambers. 

  Window frame styles

  If you have a keen eye for detail, you’ll want to choose the right frame styling and detailing for your new windows. Windows can have clear, sharp lines or a softer, curvier outline depending on whether you choose bevelled or ovolo frames.

  Another popular design choice is windows with ‘flush’ sashes. The window sits completely flat, with minimal frame depth. You might want to choose this option if you want to replicate the flat façade of traditional timber frames. However these windows do not offer the weatherproof qualities as regular frames. At the other end of the spectrum, ‘stormproof’ windows are designed so that the sashes overlap the frames, to protect against the elements.

  Period features

  Like fashion, window styles have changed over time. There are certain features that define the era they originated from. Georgian windows are overlaid with astragal bars that divide the sashes into six panes, Edwardian sash windows sported sash horns and in the 1930 arched frames were common to give a property its style.

  Good window companies understand the differences between different historical window styles and can advise you about which period features you should consider, which is especially important if you live in a period property.

  Previously, you could only expect to achieve fine detailing with timber frames, but it’s now possible to replicate this style using modern uPVC or composite materials. Some uPVC frames are manufactured with a ‘woodgrain effect’ finish, which emulate the texture of timber.

  Window seals

  Window seals, or gaskets, sit between the frame and the glazing to stop air leakage and water ingress. This results in a fully airtight and weatherproof window unit. Gaskets keep your home warm and dry, saving your frames from becoming damp and rotting. It can be easy to overlook the importance of good quality seals, but they really do help the all-round performance of a window.

  Gaskets are pre-fitted to windows before installation. With modern windows you won’t need to add any additional draught excluding seals.

  Three types of seal are needed to make a window fully weathertight:

  • Window opener seals help support the window all around its edges
  • Outer weatherproof seals prevent water from getting in from the outside
  • Inner weatherproof seals keep the window airtight and keep draughts out of your home

  Rubber vs. Q Lon window seals

  Until very recently, window seals were thick, black and rubbery, and stood out starkly against white frames. Seals and now slim and discreet, offering better insulation and contribute to a much higher energy performance.

  Seals are available in either rubber or a material called Q-Lon. Rubber seals tend to flatten once it is subject to repeated pressure, altering its shape and ultimately hindering its performance. Eventually they can collapse and this is one of the main reasons why older windows fail after a number of years.

  Q-Lon seals, however, have a compression recovery of 99%. They will spring back to their original shape every time. Available in a range of colours, to really improve the overall apperance of the window. 

• Furniture and fittings

  Window furniture & fittings

  Sometimes it’s the smallest features that make the biggest difference to your window. Whether you’re after a sleek modern look or a sculptured classical appearance, the right frame styling, handles and other accessories creates a superior level of authenticity.

  Handles

  Window handles come with key locking as standard and are usually available in a range of colours and metallic finishes to match the frame colour. Handles used to have a ‘spur’ that wedged the sash shut, but this feature is less common now that key-handles are available.

  Sash window furniture

  The key to achieving an authentic-look sash window is in the furniture. Small metal hook pulls sit at the foot of the sash, with fasteners locking the window together. Traditional weights and pulley operated sash windows also require a hook on the wall in order to fasten the cord.

  Different eras have different fashions, and it’s no different with sash windows. Professional window companies will know which sash window fittings are suited to the style of your property.

  Traditional ironmongery

  Modern windows can be made to look exactly like their traditional counterparts, right down to the furniture. Ask for traditional style handles, such as monkey tail or tear drop handles. Windows can also be decorated with peg stays, the period version of modern-day friction stay hinges, that keep a window casement open at the angle you want.

  Locks, hinges & hardware

  Your window will be constructed with different hardware depending on the materials and how you want the sash to operate. The important thing is that quality locks, handles and hinges are installed to keep your window operational for years to come.

  Check that your windows are British Standards Institute (BSI) accredited for quality and have been tested to PAS 24:2012 enhanced security levels.

  Of course, there are other ways to accessorise your new windows. You can opt for  different frame colours (including two-colour frames), decorative glazing and period features, such as sash horns and Georgian bars.

• Security

  Window security

  Installing secure windows in your home is important on a couple of fronts. Firstly, strong frames and locks can protect your home against intruders, significantly reducing the risk of break-ins and burglaries. Secondly, restrictive window openings can create a safe environment, opening just wide enough to ventilate a room without the risk of falling out.

  The best way to compare security of a window is to research the credentials. Windows must achieve the British Standards certification PAS 24:2012 – the minimum security standards required for residential properties. As of October 2015, all new build homes must be fitted with double glazing that achieves PAS 24:2012 in order to be Document Q compliant.

  Some windows also boast ‘Secured by Design’ accreditation, an initiative to reduce crime through secure glazing, backed by the UK Police. 

  Internally beaded windows

  Window glazing is held in place against the frame with a small strip called a ‘bead’ which runs along all the edges of the window sash.

  Early uPVC windows had the option of external beading, but this has largely been dropped due to security concerns. Window beads used to be a lot weaker and offered an easy opportunity for burglars to simply peel them away and remove the glass.

  Most windows nowadays have internal glazing beads, which is the most secure option.

  GrabLock - Exclusive to Everest

  GrabLock is exclusive to Everest and has been designed and developed with leading lock manufacturer, Yale. With three times the locking surface area of a standard, multi-point or shoot-bolt window lock, GrabLock is our most innovative and secure lock ever. Formed of a sleek rotating cylinder that quite literally 'grabs' a specially designed 60mm long 'keep' on the window frame, it forms an extra secure and highly effective bond.

  Made of aluminium, highly durable and non-corrosive, it's functional and durable. Offering you the best in home security and designed to be smooth-looking, stylish and discreet.

  Multi-point locking

  There are many more options regarding locks, offering varying levels of safety and security.

  Technically, a window with just two locking points can be considered “multi-locking.” The more points that can be locked, the more secure it is. There isn’t a standard number of mechanisms, but if you can find a window that has eight or more locking points, you have yourself an incredibly secure window.

  Bi-directorial locking adds a layer of complexity in the frame that prevents the intruder from being able to jemmy your window out of place.

  Key lockable handles

  All modern window handles are key lockable, making it difficult for potential intruders to simply wriggle your windows open. It also adds an extra safety feature for top storey rooms accessible by children and vulnerable. It is recommended that you leave your key inside the lock, however, so it is accessible in event of an emergency.

  Hinge-side security brackets

  Some uPVC window frames incorporate tough, interlocking brackets that secure the outside of a window sash when fully shut and locked. This means that if an intruder tries to lever the window on the hinge side, the brackets will prevent them from being able to jemmy the window out of place.

  Egress hinges

  Used for fire escapes, egress hinges allow a casement window to open fully outwards in order to provide an emergency exit.

  Opening restrictors

  Opening restrictors limit how much a window opens, either by connecting the sash and the frame via a cable, or by fitting key-lockable restrictors that allow windows to open no more than a couple of centimetres wide for ventilation purposes.

  The Royal Society for the Prevention of Accidents reports that 4,000 children under the age of 15 are injured falling from windows every year. Something that could easily be prevented by using window restrictors.

  Lockable ventilation & night vents

  Windows have the option of leaving a small, one inch gap when closing, locking them ‘nearly closed’. This is also known as the night vent position that many people use as a means of ventilation. However, leaving a window on the latch is far less secure than shutting a window fully, and can present an opportunity for a potential burglar to prise open the window.

  New windows can be provided with ‘trickle vents’ instead, which provide background ventilation without compromising the security of your home.

• Insulation

  Energy Efficient Windows

  You’ve paid for your heating so it’s the job of your double glazing to keep the heat in your home. Improvements in energy saving technology is arguably one of the most significant developments over the past few years, not just for the environment but for home comfort and money savings, too.

  Up to a third of heat in the home is lost through single glazing. By upgrading to energy efficient windows you can save around 20% in energy use. Thermally efficient windows are at least double glazed, with low emissivity glass and an inert and non-toxic insulating gas like Argon between the panes.

  Combined with energy efficient frames, new double glazed windows can achieve up to an A+12 Window Energy Rating (WER), and triple glazing can achieve up to A+32. Upgrading your windows could save you up to £450 on household bills every year.

  WER rating

  The British Fenestration Rating Council (BFRC) created the WER rating (Window Energy Rating) in order to simplify how effective a window is. The rating system offers grades from A-G (with A being the best). If the window is rated higher than an A it will be followed by a number, and anything above an A10 becomes A+. In October 2015, the BFRC introduced the A++ rating for windows that achieve higher than A+20. The highest rating currently available within the UK is A+32.

  The WER rating is made up of three key elements: U value (low heat loss), solar gain and air loss through ventilation.

  1. Thermal efficiency (U value)

  A window’s U value is the technical way to measure heat loss through a type of building material, such as a brick wall or tiled roof. U values are calculated by the equation W/m2k, which measures heat loss in watts (W) per square metre of material, when the temperature (k) outside is at least one degree lower.

  The lower the U value, the better the insulation provided by the material. Single glazed windows have a typical U value of 4.8-5.6W/m²K, meaning that around 5 watts of heat are lost per hour, for every square metre. Modern double glazing can achieve a U value as low as 1.4W/m²K, and triple glazing is even more energy efficient, reaching 0.6W/m²K. This is lower than the U value of an external wall!

  2. Solar gain (G value)

  Solar gain is another factor that can boost a window’s energy rating. Not only are windows now designed to stop heat escaping, but they can also let heat in by capturing the sun’s rays. The idea is to capitalise on solar radiation as a natural or ‘passive’ form of heating, reducing the dependence on carbon energy to heat your home in the winter months.

  Factors that influence the solar factor include the number of panes, the type of gas between the them, and also the type of coatings added to the windows, as they dictate whether the glass absorbs or reflects the heat. It is measured by the G value, on a scale between 0 and 1, with a high number indicating high solar gain.

  Contrary to what you might think, solar gain windows do not always lead to overheating. The UK has a relatively cool climate and relatively little sunshine, so overheating is rarely a problem! For rooms where sun streams in during the afternoon, it could be worth considering upgrading to triple glazing. The level of solar gain is actually less than double glazing, due to the extra pane of glass and cavity.

  3. Air leakage (L value)

  Air leakage occurs when there is a weak point around the window frame, such as the seals. Most modern windows are fully airtight, and should have an air leakage factor or L-value of zero (0.00W/m²K).

  Air leakage is not to be mistaken with ventilation. Ventilation is a controlled system, letting in small amounts of fresh air to reduce stuffiness and improve air quality, whereas air leakage will compromise the energy efficiency of your window.

  Sound insulating windows

  Upgrading to Acoustic windows will go a long way to improve sound insulation in your home. The effect is like as moving a road that’s just 5m from your home another 100m away. Resulting in a quieter and more relaxing living space, free from the noises of traffic from roads and flight paths.

  If you’re restricted by conservation planning rules, secondary glazing can also help to reduce the noise from outside filtering into your home.