WINDOWS BUYING GUIDE

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.

Casement windows

'Super windows' that offer the benefits of many materials combined.

Casement 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.

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 be greatly improved 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.

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? It depends on your priority - Triple glazing is more thermally efficient, offering the highest window energy ratings. The Everest triple glazed window is A++22. If your priority is noise reduction, double glazing is likely to give you a better result. This is because the middle pane can increase sound vibration and amplify sound transference

For some properties, triple glazing isn't high priority, but it will improve heat retention for colder rooms that are north-facing.

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 noise reduction 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.

Acoustic glass

Acoustic 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.

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.

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

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 outer frame 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 appearance of the window.

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.

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 24:2016 – the minimum security standards required for residential properties.

Some windows also boast 'Secured by Design' accreditation, a flagship UK Police initiative to help 'design-out' crime through the use of high-quality innovative products.

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.

Energy Efficient Windows

You've paid for your heating so it's the job of your double glazing to help 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 make a saving in your 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 an A+ Window Energy Rating (WER), and triple glazing can achieve an A++ Window Energy Rating (WER). Upgrading your windows could enable you to make a significant saving on your 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 WER rating is made up of three key elements: U value, solar gain and air loss through leakage.

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 reduce 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.

Acoustic windows

Upgrading to Acoustic windows can help to improve sound insulation in your home, . resulting in a quieter and more relaxing living space.

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

The lifespan of a window depends on the quality of the product and workmanship. A well-made and well-fitted window won't have to be replaced for decades.

Warning signs for needing to replace a window are:

1. Misted windows due to blown double glazed unit (failure of glazing seals)
2. Timber frames have warped or started to rot
3. Plastic has perished, is peeling or discoloured
4. Windows rattle, or let in draughts and the cold
5. Sashes don’t open or close properly
6. Broken hinges, handles and locks

Another reason to look at upgrading to better performing windows would be to improve the insulation within your home.

It's common to experience these problems if your windows are over 20 years old. Sometimes it's possible to repair a window, but like a car, replacement parts will only delay the inevitable. At some point the window will need to be replaced.

Had your windows replaced recently? Alarm bells should be ringing. If you're experiencing these problems so soon, it's likely that the window is faulty or has not been installed correctly. It's worth checking to see if you have an active warranty (most companies offer a 10 year guarantee) or get in touch with your double glazing installer to see if they are able to rectify the problem or replace the damaged unit.

The majority of windows are replaced like-for-like, and for many this means choosing white uPVC. However, modern windows are available in the largest range of colours to date, and you're not limited by the material you choose any more. uPVC windows are available in natural wood colour frames, aluminium windows come in contemporary blacks and greys, and both can be 'dual coloured' for a different frame colour inside and out. Heritage tones are surging in popularity, including Chartwell Green, Cream Woodgrain and Anthracite Grey.

If you need more help choosing a colour scheme for your windows, ask your consultant for advice tailored to your property.

Up to a third of burglaries in a home occur through a window. This could involve smashing the glass (single glazed windows are particularly easy to break), removing external frame beads to simply lift the glass out, or levering open the sash. A window is only as secure as its weakest part. Ensuring the frames, hardware and glazing all work together to prevent entry is fundamental for your home's security.

Good windows have multi-point locking, a key lockable handle and strong frames and hinges. A simple way to check for enhanced security credentials is by assuring that they have been certified to PAS 24:2016. Another tip is to hide your valuables from view with curtains or blinds.

Around 15% of burglaries don't involve any kind of forced entry, with intruders climbing through an open window or door. It's important to remember to keep windows shut and locked when you're outside of the room, but if ventilation is important, consider tilt-in windows that only leave a small opening.

If you live in a listed building, conservation area or your house has a restrictive covenant, you'll need to follow certain guidelines to ensure your new windows are "in-keeping" with the surrounding area.

Houses in conservation areas are subject to 'Article 4 Directions', which restrict the work that you can do to the outside of your property, without first getting planning permission. If this is the case, it's often simpler to find a company with previous experience of getting windows accepted in conservation areas. Ask your window company for details of previous projects that have been accepted by Planning Officers.

Other than these legal necessities, it's up to you what style, colour and glass designs you want for your windows.

Conservation areas are in place to protect architectural and historical buildings or places of interest, and are more common for properties built before the turn of the 20th century. However, it's always worth checking before going ahead with any home improvements. Homeowners who go ahead without planning permission may be required to pay again for a more sympathetic upgrade.

You can find out if you live in a conservation area by contacting your local planning authority (LPA), and you can find out if you have a restrictive covenant by checking the title deeds for your home.

Unless your house has a legal obligation to retain its appearance, it's your choice. Many people choose a traditional design to fit with their home's appearance, but in some circumstances modern, slim frames can actually enhance the aesthetics of a property.

If you're totally stuck or need some advice, get in touch with a home improvement expert who can help you choose windows that suit your property.

Modern, high performance windows should last for decades to come, needing only minimal maintenance. Some parts now come with lifetime guarantees, meaning that you will never need to worry about plastic frame discolouration or misted windows.

uPVC and aluminium frames are practically maintenance-free, and only require cleaning occasionally by wiping down the frames with a damp cloth. Timber windows can be cleaned in the same way, but will also need to be recoated using microporous paint or stain every couple of years, when necessary.

One way to make your house more energy efficient is to upgrade to better glazing. Single glazed windows lose a house up to a third of its heat through the panes, meaning if you still have single glazing, you could make a significant saving, just by upgrading your windows.

Energy ratings for windows are often calculated by two different systems – Window Energy Rating (WER) and U values. WER ratings are presented on a simple A++ to G scale, to make it easier to compare windows across the board. U values make up part of this rating, and they are the technical way to measure heat loss.

You can ask your window company for both these specifications when deciding on a new window. They should be able to show you a Window Energy Rating for the product, or you can look at the BFRC website at www.bfrc.org. Average double glazing achieves around a C rating, but superior windows can achieve an A+ rating. Triple glazed windows can reach an A++ rating, the highest window energy rating.

It's worth noting that the energy efficiency of a window is only as good as its installation. A poorly fitted window with gaps around the edge can leak heat and create draughts. That's why it’s important to choose a company that makes your windows to measure, so that they fit the aperture perfectly, and properly seal the perimeter.

It's important to make sure your new windows are guaranteed for a number of years after installation, for your peace of mind in case something goes wrong. Better windows often come with longer guarantees. Look for a window company that offers more comprehensive cover, including guarantees against foggy glazing, discoloured frames and faulty parts. Some companies even offer lifetime guarantees, with the option to transfer the warranty across to future home owners.

Also, look for a company, such as Everest, that is part of a competent persons scheme, such as FENSA. It is a mandatory requirement of schemes like FENSA that companies must provide a guarantee insurance policy that would cover any rectification work, should the company become insolvent, for a period of 10 years from the date of installation. Make sure that you're provided with the relevant documentation and information for how to claim in the rare case that you may need to.

You can tell if the timber in your new windows is sustainably sourced by selecting windows that receive FSC accreditation – approved by the Forestry Stewardship Council. Window frames are made using wood from a responsible source, i.e. trees that grow quickly and in managed forests to slow the impact of deforestation and reduce the impact on the environment.

European Redwood is an example of a plentiful softwood that is used in window construction, and is approved by the FSC, for an environmentally sound window.

CE marking for windows essentially means that all windows from the same manufacturer are of a consistent quality, and is a necessary accreditation for all products made and sold in the EU. Make sure that you choose a double glazing company that installs CE marked products. They should display the logo in their literature and double check the product by looking for the logo both on the inside of the frame and the sealed glass unit.

Any good double glazing installer will survey your property and precisely measure up for new windows before giving you a quotation, meaning that every window or glazing product you buy should be made to measure your home. Most installers can make or order windows in any size and shape, depending on building regulations, including circular, arched top, apex or triangle shaped, or angular windows. Simply ask your local representative during your design consultation.

• Accreditations - There are many industry renowned federations and bodies who take great efforts to ensure that the best window companies are easily identified. The main ones to look out for are GGF, BFRC, FENSA, Conservatory Association, TGO and BBA. Click here to read more about each accreditation.
• Experience - A good reputation are good indicators of a stellar window company. Focus on the company's reviews and satisfaction ratings. Ask to see examples of recent work, including customer testimonials and installation pictures, to make sure they are confident with undertaking similar projects to yours. It's also worth asking about the professional experience of the team. Does the company have dedicated and experienced advisors, surveyors, installers and project managers?
• Recommendations - If you're stumped about where to start, talk to people you know and trust about any personal experiences they may have had. That will give you a good idea of the level of service that different businesses offer.

Friends and family are a great starting point when getting advice about buying windows. TV, magazines and the internet are limitless sources of inspiration. But nothing beats seeing the options laid out in front of you, with samples so you can get a feel for the windows themselves.

Before you buy, see if any of the companies you like offer a no-obligation consultation service. If they do, there is nothing to lose by arranging an appointment, which will give you some face-to-face time with an expert.

Narrow down your list to companies who actively install in your area. Not only will this save you time in your search, but you can be confident that they have experience with similar house styles.

Typically, you can expect to have your new windows installed about 6-8 weeks after ordering, but the wait time is different with every company. This can be due to a variety of factors, including manufacturing complexity and arranging any planning permission, as well as popularity of the company and seasonality. As long as the company is responsive and communicates at every step of the process, it is the sign of a good service.

The time it takes to install a window depends on how many windows and other home improvements you're having installed at the same time. A single window will typically take approximately 3 hours to install. Your window company will be able to give you an estimated installation time when booking the installation date.

Even if you're confident you've chosen the best glazing company and best quality window, it's good to know that you can call on your installation company again at any time within the guarantee period. Whether you want advice about looking after your windows or troubleshoot any problems, it's a relief to know the full service is available to you.

Ask about their aftercare service, and whether they offer callouts and free repairs if anything goes wrong. It's unlikely you'll need to use such services, but it's a shrewd idea to check beforehand.