A definitive guide to glazing - Westbury Windows and Joinery

Our guide to glazing: windows, doors and roof lanterns

Glass has to be among the most serviceable and diverse construction materials we have available to us. It also happens to be one of the most resplendent. We explain the ins and outs of this timeless material and show you how to choose the right glazing options for your home.

Architects and homeowners alike appreciate glazing for its ability to let in plenty of natural light into a property and make your home feel more connected to the outdoors. New or replacement windows are often a go-to solution for many home improvement and new-build projects. Humans have always had a need for natural sunlight, not only to help us see what we are doing inside our homes but we also need it for our physical health and wellbeing. In addition to windows, glazing is often a popular material for extensions, flat roofs and entrance hallways. However, many people are surprised to discover that glazing is not necessarily a simple purchase – in reality, there are many factors to consider before making your decision.

A closer look: the history of glass windows

It is hard to believe, but archaeologists have found evidence of humans using blue glass in either Mesopotamia or Lower Egypt in 2500 BC. Interestingly, the first glass-making manual dated back to 650 BC with glassmakers carving instructions into stone tablets. Explorers discovered the artefact in an ancient library belonging to a Neo-Assyrian King. Nothing else changed until the Venetians discovered the technique of glass blowing in the 1st Century BC, and this revolutionised the industry. The first window panes were roughcast into a wooden frame onto a layer of sand or stone. 

In the 16th century, windows in England were basic stone or timber openings that could be covered with oiled cloth, paper or wooden shutters. Glass windows were exclusively reserved for the wealthy and prominent figures in society, and they were tiny panes of glass set in lead strip latticework. During the Tudor period, windows increased in size, and larger households would use windows to display their wealth. 

Consequently, the advancements of many other glass inventions increased over the decades, from mirrors and glass spectacles to stained church windows and microscopes. Thanks to the innovative minds of scientists throughout history, glass now comes in many forms, from clear crystal glassware to tempered glass, float glass, fluorite glass and bulletproof glass. 

An American named C.D. Haven created an early version of double-glazing in the 1930s and named it ‘thermopane’. It was hugely successful throughout America in the 40s and 50s. By the 70s and 80s, it had also become popular in the UK. You can find out more about the rise and fall of timber windows in our other article. Nowadays, double glazed windows are considered the norm. Back in 2018, Part L building regulations for standard replacement doors and windows put greater focus on a property’s energy efficiency. Now, a glazed product should have a U-Value no higher than 1.6 for windows, and 1.8 for doors.

U-Values matter!

U-Values, help us to identify a material’s energy efficiency, and the lower the number, the higher the insulation. Essentially, it is a measurement of how much heat and energy a window, door or roof lantern lets through.

A reliable joinery company should be able to inform you of their product’s U-Value, which they have measured using a thorough performance testing process. Many companies do not typically offer the U-Value of the whole product. If they only disclose the U-Value of the product’s centre, then be wary. Their information might not account for the frame’s thermal performance, which is always lower. Leaving this detail out will make their product’s U-Value look better than it actually is. 

Bear in mind, energy efficiency does not just look at the heat being lost from your home. The industry determines a window’s performance based on its solar gains versus heat losses, both of which are vital for creating a comfortable temperature inside your home throughout the year. 

Solar gains depend on the share of solar radiation passing through the window. In the depths of winter, you will want your windows to maximise on this effect. During the warmer months , lower solar gains and ventilated cooling are more appropriate. Heat losses are dependent on the outdoor temperature, and the window’s ability to retain heat. Solar irradiation is also affected by the window’s position to the sun. 

Westbury Windows and Joinery independently test all of the products at an accredited centre. Our windows have a whole product U-Value of 1.4 W/m2K based on double-glazed glass and 1.1W/m2K, based on triple-glazed 4mm thick glass, with a centre pane value of 0.6 W/m2K.

Glazed entrance doors

Glazed doors can come in a range of designs to suit your home and your tastes. From doors with sidelights and fanlights to glazed vision panels, there are plenty of styles to consider. Whatever look you opt for, a glazed external door is a perfect option for transforming a dim entrance hall into a light and bright space.

A glazed front door offers an ideal balance between security and transparency, with plenty of opportunities to maintain your privacy at the same time. Your supplier can install glazed vision panels into the front door itself; you can opt for two, four or even six glazed panels in your door, depending on the style you want to achieve. Sidelights are narrow windows fitted to the side of an entrance door and can be used to mirror the style of the door or add more glazing to your home’s entrance. Borrowed lights are suitable if your property has a smaller entrance opening with no room for a sidelight. Looking just like an opened fan, they sit above the entrance door and can sometimes have decorative lead detailing. 

Glazed roof lanterns

A roof lantern’s perfectly balanced design can completely alter the look and feel of your property. They are ideal if you have a flat roof, such as a single-storey extension, for example. Unlike a simple skylight, a roof lantern can heighten ceilings and offer beautiful and expansive views of the sky above. Their ultimate purpose is to allow as much natural light in as possible – but if the wrong glazing is used, the room below can feel hot and stuffy in warmer temperatures. It is best to use glazing with a solar glare coating, which will help to reflect the solar heat back off the roof lantern. It is an ideal glazing option if your roof lantern is south facing, as it decreases glare and heat build-up in the room while maintaining a high light transmission. 

Westbury timber roof lanterns are double-glazed with 4-16-4 toughened panes. The glazing is filled with insulating argon gas and sealed with a Low E coating as standard, to ensure comfortable temperatures all year round and leads to energy saving. If needed, we can upgrade the glazing to laminated, low-maintenance, or solar reflective glass.


Glazed timber windows

Glazing is available in a full range of options depending on your window requirements. For example, you may live under a flight path and want Sound & Secure Extra glazing for maximum noise reduction. Alternatively, you may be building an eco-house and want to opt for triple-glazed windows. What’s more, high-quality double-glazing can be filled with krypton, which results in as much energy efficiency as argon-filled glazing but allows a thinner, classic aesthetic. This traditional-looking glazing is ideal for period homes, which might not look right with thicker double-glazed windows. 

Toughened glass is perfect for use in balconies, landings, and staircases, or windows that are high up. It has one laminated pane, which helps to hold the glass in the frame and stop smaller, shattered pieces of glass falling on anyone if it breaks. 

The same glazing that we use in roof lanterns can also be great for windows used in rooms that are either too warm or too cold, depending on their exposure to the sun. With a Low-E coating, these windows reduce heat transfer and reflect the sunlight back outside. Warm edge spacer bars insulate the edges of a sealed glazed unit. They keep the panes apart to prevent cold bridging. 

Westbury standard glazing is 28mm thick and is fitted into its rebated unit with double-sided adhesive tape and secured externally using a secret nail system through the Accoya® glass bead. The external perimeter is permanently sealed with an appropriate colour silicone.

Westbury manufactures elegant, bespoke timber windows, entrance doors and roof lanterns. Every product produced is made from the finest quality sustainable timber and performs perfectly for the modern home. If you would like to speak to us about an enquiry, you can contact us and we will be delighted to talk through your ideas and advise you accordingly.