How thick and heavy is TG compared to a conventional window?

When considering an upgrade to triple glazing, you may be concerned with a few factors: will I find a style that will suit the style of my home? Can my existing windows be converted to triple glazing? And will my home’s structure accommodate the increase in weight and thickness?

Especially in older or conservation homes, these are valid questions.

Let’s first look at the issue of style. Triple glazing windows make use of the latest materials and technology in both their frames and glass. The frames are available in wood, aluminium, uPVC and aluminium-clad wood and can be manufactured to suit any architectural style and any window size.


Wooden frames

Wooden frames are a popular choice because of their natural look. It’s the traditional choice that adds character to the exterior of a home, and warmth to its interior. Wooden frames can withstand harsh weather when treated and maintained properly, but as a consumer you should insist on wood coming from a sustainable source. While one of the more expensive frame materials, it is certainly one of the most beautiful.


uPVC / Aluminium frames

uPVC, or unplasticized polyvinyl chloride, can be manufactured to look like wood, but it requires very little maintenance. uPVC frames are also exceptionally strong and stable, so they won’t warp, rot of fade over time. The frames are moulded, which allows an almost limitless variety of textures and colours. This customization makes it a highly sought-after material for triple glazing frames, especially where conservation windows are concerned. This material is also water and fire-resistant and doesn’t scratch or damage easily. It is also recyclable, giving it a great environmental rating as well.

uPVC frames as well as aluminium frames are considerably lighter than wooden frames of the same size. Where the structure of the home is a concern, uPVC and aluminium frames should then be considered when upgrading existing single or double glazed windows to triple glazing.

When replacing like with like material however, the only real consideration is the added pane of glass. A standard double glazing window frame is between 70 - 95mm thick. Triple glazing frames are much the same, so it’s just the weight of the additional glass and not so much the frame that will make it heavier.

A pane of 4mm glass weighs roughly 10kg per square meter. A double glazed window therefore weighs around 20kg per sqm, and a triple glazed window 30kg per sqm. A standard window measuring 400mm x 1200mm will weigh 9.6kg when double glazed, and 14.4kg when triple glazed. Of course, as the size increases, so does the overall weight. But unless your home’s windows are disproportionally big, the structure will be able to handle the additional weight.

When your preferred triple glazing installer comes to your home to inspect your existing windows, he will also be able to do an assessment of the structural condition of your home and the viability of having triple glazing installed. Where there is cause for concern, he will enlist the help of a structural engineer to make a professional recommendation.

Once area where the size and weight of a window may be a concern, is with installation. Cranes and lifts or other specialized, heavy-duty site handling equipment may have to be used if the windows are too big to handle manually, or too high to reach safely. Your triple glazing installer will advise you on this as well.



Under what circumstances may my walls not be able to carry the weight?

There is always a concern with older homes where the structure may be weaker than in modern buildings. The building material used and the condition of the structure will have a big impact on the viability of new windows.

If you are in doubt in any way, it is best to consult a structural engineer before you get a triple glazing installer involved. Let them come and do a survey of your property and determine whether it will be able to handle the additional weight. This is especially relevant where a second or third story is present.

While triple glazing can be manufactured to any size, very large windows may require a thicker glass and a custom-made profile. In commercial buildings that make use of external glass cladding, glass thickness is increased to compensate for the weight of the panel and to prevent stress-cracking. This same principle can also be applied to domestic installations where necessary.

Triple glazing is also very sympathetic to conservation homes, where very strict design guidelines apply.

Since 1967 there have been more than 9,300 areas across England designated as conservation areas. This designation gives the local authority extra controls or demolition, minor developments like the inclusion of dormer windows in roof renovations, and installing satellite dishes which are visible from the street.

It is the responsibility of the local council to be the custodians of the conservation area and to prevent the character of the area from being lost through over-development and modernization. While this may pose problems for homeowners wanting to modernise their properties, they fulfil an important role in preserving original and traditional architecture and their decisions should be respected as such.

In 1995, the introduction of Article 4 Directions gave the local authority the power to enforce further restrictions on the type of alterations that are allowed, based on how these changes may affect the key elements of the other houses and buildings in their specific conservation area. This includes painting a house in a different colour and replacing distinctive windows and doors.

While some conservation officers and inspectors argue that anything other than single glazing is not authentic, the energy efficiency, cost reduction and environmental impact of upgrading to more efficient windows are a great motivator in getting triple glazing window upgrades approved.


Windows are a very important design feature of any building and even small changes have a big impact on the building’s appearance. Many factors contribute to the look of the window: the position of the window in the building, the arrangement and composition of the glass, the joinery style and the frame thickness. In a recent English Heritage survey, it was found that the biggest threat to 83% of conservation areas, was the unsympathetic replacement of doors and windows.

For this reason, most local authorities in conservation areas prefer original windows to be replaced with more efficient windows in traditional wooden frames. The same survey done by English Heritage found that out of the 360 local authorities surveyed, 13% had an article 4 Direction in place that gives them the authority to prevent the installation of non-wooden windows.

What many homeowners may not realize, is that the installation of incorrectly detailed windows and doors, while improving their Energy Performance Certificate, could actually have a damaging effect on the value of their home.

These facts are only relevant to conservation areas however. If your home is in a listed or historic building, then only single glazing, installed with putty and using historic glass will be allowed. Broken or damaged sections of the frames can be repaired or replaced with an exact replica, while hardware, mechanisms and sash cords should be repaired where possible, or otherwise replaced with an exact replica. But for any work done to a listed building, the proper Listed Building Consent should first be obtained.

When you are looking to replace your existing windows then, it is essential to get the expertise of an accredited installer who will be able to guide you through not only the building regulations, but also advise you which style of window you will need to consider.

Published on : 23th February 2017

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