August 10, 2015

How to Add a Glass Extension to a Listed Home

Written by Rebecca Clayton

Yew_Tree_House_listed glass extension

Is a glass extension the right choice for my listed home?

When wanting to extend or renovate a historic or listed building, the integrity of the original building and design is something that must be carefully considered.

A listed home in England is a protected building of particular architectural or historical significance. By being ‘listed’ the property is protected from unrestricted alterations in an effort to maintain the cultural significance of the building.

glass extension is an extremely popular option when looking to extend a listed home for many different reasons.

The transparent nature of a structural glass box extension does not hide the original building design, maintaining its architectural design. The clear definition between what is a new extension and an old building helps protect the character of the home.

glass box extension with steel structure on a listed london home

So, how to add a glass extension to a listed home?

A cohesive design is important and a listed building consent application is much more likely to be successful if they are led by an architect, but ensuring that your glass extension design is carried out by an experienced glass contractor is an important contributing factor.

Double height glass extension to Grade II listed home in London

The use of Low Iron Glass is usually recommended when looking to add a glass extension to a listed building. Low iron glass is a clearer glass product than standard clear glass. It is manufactured with a lower iron oxide content and therefore creates a more transparent glass structure.

These structural glass boxes can then be supported by frameless structural glass beams and fins, made from Low Iron Glass, to ensure a fully glazed and transparent structural glass installation. IQ design glass beams and fins with Low Iron Glass as standard, eliminating the naturally occurring green tint that occurs in exposed glass edges.

If any opening doors are required, opt for as slim a frame as possible. If no thermal performance is required to the glazing (when being used as part of a conservatory design rather than extension) the doors needn’t have any frame at all. If a level of weather sealing and thermal performance is required then sliding doors will afford you the slimmest frame, reducing the amount of obscuration between the outside and listed building structure.

Side infill glass extension to Grade II listed house

In some cases, you might consider the use of non-reflective glass which is made from Low Iron Glass with additional coatings on the glazing to reduce its reflectivity. If this solution is specified, the glass is nearly invisible to passers-by and will greatly reduce the impact of any new addition on the character of the listed building.

When looking to extend a listed building with a glass extension precision is the key. Ensure you have the right permissions in place (adding an unauthorised extension to a listed building is a criminal offence), use a suitable architect and seek the advice of an experienced architectural glazier who will design and install. Our in house developed structural glazing system, Invisio, has been designed to achieve the most minimal appearance without compromising modern performance values.

When using Invisio to engineer a glass box extension opening elements can be incorporated within the frameless glass design, including slim framed sliding glass doors.

Asking your architectural glazing company for previous examples of extensions to listed buildings might help your planning application. IQ have worked on a number of heritage and listed buildings and have a wealth if knowledge in complex projects of this nature.


To speak to us about adding a glazed extension to your listed building project, email us on