Technical Advice | Structural Glazing

A Beginners Guide to Glass Box Extensions

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Rebecca Clayton

Written by Rebecca Clayton

Edited by Dan Finnegan

Fact-checked by Michal Piekarewicz

Aug 19, 2026

Last verified: Aug 19, 2026

Next review: Aug 19, 2026

Our Editorial Process - How We Write Our Technical Advice Articles

01

We pick topics from real questions we hear or see being asked

We do not make up topics just to get clicks. Our topics come from the questions people really ask us. Architects ask us when they plan a building. Builders ask us on-site. Homeowners ask us when they plan their project. If the same question keeps coming up, we write about it.

02

One of our internal experts writes the first draft

The first draft is written by someone who works with that glazing system. This might be a technical advisor, a designer, or a product expert.

They write using three things, in this order. First, our own finished projects and what we learned from them. Second, the building rules and the glass standards that apply. Third, the maker's technical data for the system we supply. When we give a number or a limit, we say where it comes from. We name the rule or standard and link to the official source so you can check it yourself.

03

A second expert checks it

Before any article goes live, a second qualified person reads it. They check three things. That the facts are right and not made too simple. That any rule or standard we mention is current and stated correctly. That the advice matches how the work is really done on site.

This checker can send the article back, ask for proof, or stop it from going live. Two experts must agree. This is the most important safety step in how we work. The name of the person who checked each article is shown on the article itself.

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Will a glass extension suit my building?

Although a glass box is seen as a futuristic addition to a building these types of clear extensions suit traditional builds as much as a contemporary new home.

Due to the inherent appearance of glass – it is clear – it allows you to see the traditional build behind and there is a clear difference between what is new and what is old. These types of frameless glass extensions can sometimes appease planning officers that don’t want to disrupt the integrity of the buildings original architecture.

From an internal view, a glass extension brings more of your garden into your internal space, so make sure your garden is something to look at! Don’t overlook garden design and external lighting when you have a glass box extension to the rear.

What Design Options are there?

The design options for a glass box extension are endless. From a full glass box with clear glass on all sides to the introduction of solid elements, like a solid roof, a glass extension can be designed to suit your space.

Various framings, supports, opening elements and shapes can be used through IQ’s bespoke glass extension designs, incorporating all elements of specialised glass solutions from Glass Beams to aluminium casement doors.

A popular modern option is to include a solid roof with glass faces on all open sides. These can be constructed from fixed structural glass or minimally framed sliding glass doors for a contemporary appearance.

Side infill extensions normally have one solid wall along the party wall line with a glass roof and vertical opening glass element to the garden.

Glass Box Extension

What Doors can I use?

IQ Glass can incorporate any of our specialised window and door systems into a structural glass box assembly. Bi Fold doors allow you to open up the whole face of the bespoke glass extension whereas sliding doors will give the space the slimmest sightlines available of 21mm.

For smaller extensions or smaller openings, you could use a minimally framed pivoting door or a standard aluminium casement door.

Where a different design approach is wanted you could also use IQ’s flush glazed doors for a sleek external appearance or our Modern Art Deco doors in the Mondrian® range, recreating a more industrial steel effect in a well performing slim metal frame.

IQ Glass Extensions

What about options for the glass?

The glass panels used within the glass extension can have any number of specialised finishes applied to them to make sure your glass box extension suits the building and area it is constructed in.

Low Iron Glass is great for conservation areas or extensions where the transparency of the glass extension is important. Solar Control Coatings are also popular for these types of highly glazed environments to reduce the amount of solar radiation travelling through the glass to reduce solar gain.

In marine environments, IQ would suggest the use of Low Maintenance coatings to reduce the amount of cleaning needed to large glass constructions in these areas where there are more deposits in the atmosphere.

For very technical glass solutions IQ Glass can construct a glass box extension from clear Heated Glass units which will act as the sole heat source for your extension as well as create the glass walls.

Will I Need an Architect?

For these types of high design, bespoke extensions to homes IQ Glass always recommend to use an architect. They will be able to notice and address issues with your wanted design, create an eye-catching addition to the building and make efficient use of the space you have.

The involvement of an architect on an extension project will also mean that your designs have a greater chance of getting through planning permissions if needed.

Will I Need Planning Permission?

If your building is listed or in a conservation area you will always need planning permission. Most small extensions are covered by the governments Permitted Development Rights. Read more at our learning article – Will I Need Planning Permission?

Glass Extension