Glazing Applications

Glass in Listed Buildings

ansty-manor-listed glazing

Glass in Listed Buildings

Listed Buildings are protected for the national interest because of their architectural or historical significance. Listed Building status is applied to preserve and protect the unique and best examples of the countries rich traditional heritage for future generations. Without the strict permission of a planning authority, a listed building in England is not allowed to be altered in any way, shape or form. 

Small repairs and maintenance work is usually acceptable as long as it doesn’t alter the historical aesthetic of the building. If an individual was to proceed on alterations to a listed building without the required planning permission then the individual is at risk of facing criminal proceedings and the cost of undoing the work will be covered by the guilty party.

There are about half a million structures already on the listed building list in the UK. The older the building, the more likely it is to be listed; any building built before the 1700’s and most buildings dated between 1700 and 1840. Some buildings between 1840 and 1945 may likely be listed if they have an exceptional design or have historical significance. Any building under the age of 30 is not listed.

What are the different Listed Building grades?

Buildings eligible for Listed status vary immensely and so are categorised by grades: Grade I, Grade II* and II.

  • Grade I status is applied to a building of outstanding and special interest, 3% of all listed buildings fit into this category.
  • Grade II* status is applied to significantly special buildings but is of not as much special interest as Grade I buildings, 5% of all listed buildings fit into this category.
  • Grade II status is applied to buildings of special interest but are not of as much importance as Grade II* or Grade I, 92% of all Listed Buildings fit into this category and the planning office is usually less stringent on granting permission to changes to a Grade II listed building.

In Scotland, Listed status is classified a little differently; more details can be found in this guide.

Glass in Listed Buildings

Architectural Glazing is a highly successful building material when renovating or updating a listed or heritage building. Highly contemporary, fully glazed extensions or glass additions to listed buildings are often preferred by planning officials and bodies such as English Heritage, as the contrast between the modern glass and original building very easily defines what is new and what is old.

Glazed elements are the preferred additional material to heritage spaces due to the glass being naturally transparent; it therefore does not block the view of or alter the original design of the protected building.

Once glass has been decided as the building material of choice for your listed building renovation the next step is to ensure that the glass does what is required; serving whatever function is required for the design and building specification.

Why retain Historic Glazing?

Before making changes to your current windows it is important to understand the original design. Many windows manufactured in the 1800s were hand-made and were very delicate, only used on very wealthy properties and by rich landowners. Historic glazing is usually very thin and fragile but has a very eye-catching aesthetic.

If you’re looking to have historical windows replaced you must apply for approval to ‘listed building consent‘. The aim of listing a building is to not prohibit change but to make sure that any alterations are in keeping with the current design and age of the building.

The local authority conservation office will produce a thorough and detailed assessment of your proposal for changes and then deliberate on whether or not approve or reject your proposals.

What property owners need to be aware of is if the local authority grants approval for window replacement then a property survey may still be required to make sure and confirm that the windows definitely require a replacement.

Clear Frameless Glass

Where glass structures on listed buildings are required to be as minimal as possible the use of structural glazing is the best tool. Structural glass is a bespoke architectural glazing technique that utilises the inherent strength of glass to create frameless installations of glass.

>The connection between the structural glass and the listed building is important and should be designed individually for each listed property by the glazier. The structural glass fixings need to be minimal but also need to be fixed to the listed structure in a way that maintains the integrity of the building fabric.

Structural Glass Box Extensions

Glass box extensions make for a lovely contemporary addition to a listed property. Ansty Manor is a beautiful 16th-century historic structure. The building is above the 1-acre lake and is classed as Grade II*.  The frameless glass was used to link the modern and traditional stone construction of the manor house with the use of a frameless glass link. The addition of the glass extension allows the living space to be naturally lit throughout the day. The glass extension allows visitors to see through the glass wall and appreciate the incredible stonework and features of the listed building. The structural glass is supported by frameless glass beams. The frame of the sliding door is ultra slim and helps to reduce any obstruction to the listed building.

Mondrian® Glazing

The Mondrian® Glazing systems are a collection of artisan steel windows and doors that beautifully replicate the traditional industrial or loft-style windows on many listed properties. The range includes non-thermally broken solutions that exactly match the design of traditional steel windows and use the same profile as many well-known traditional steel systems. These steel framed glazing systems can be incorporated into a glass box extension design, like in our Gatsby House, listed home extension project.

Sieger Legacy

If you are able to use an aluminium profile for your heritage glazing design then the Sieger Legacy collection is your first choice. The range of thermally broken aluminium windows and doors offer a traditional design to the profiles with slim sightlines. This replicates the appearance of a steel system without the additional costs of working with steel. As the aluminium frames can be powder coated any RAL colour (or a selection of specialist finishes) you can ensure the installation matches the heritage design.

Specialist Glass Technology

For a clearer finish to your glass installation low iron glass can also be used with great effect on listed buildings. This specially processed glass has a much better clarity than standard toughened glass as it has a lower iron content to reduce the amount of green tint that naturally occurs in glass. This creates a clearer barrier on the glass elevation or installation.

Low iron glass can be especially useful in structural glass installations which use thicker glass specifications than framed solutions. When thicker glass compositions are used the green tint in normal 'clear' glass can be more noticeable.

It is important to keep in mind that low iron glass may not always be necessary for your glass specification, especially if the glass unit includes any coatings (such as low e or solar control). The team at IQ will be able to advise you as to whether low iron glass will be a useful investment for your glazing package and offer technical data on the light transmission and G factor of your glass specification.

Anti-reflective glass is another useful tool for listed building renovations. The glass goes through a specialist finishing process to reduce internal and external reflection from the glass panel resulting in a glass unit that is almost invisible. This solution is particularly effective when the glass is being used as a barrier between spaces, such as glass extensions, links or to block-in existing openings.

The Glazing Design & Install

When altering or refurbishing listed or heritage buildings ensuring that no damage is inflicted is another large consideration.

IQ use specialist surveying and fixing techniques to ensure that all our pre-bonded angles are perfectly positioned with the listed buildings mortar joints.

Using the latest in surveying technology, IQ’s surveyor can create a 3D model of the opening and all brick or stone joints in CAD, giving IQ an accurate vector model of the building on which we will be working. This enables our experienced designers and fixers to install glass panels without damaging the brickwork of listed buildings.

All finishing to listed buildings must be detailed and intricate in order to maintain the honour of the original work. All design details must be created individually for each project to ensure that the design and detailing is correct and applicable to each application.

Above all else you must ensure your architectural glazier has proven experience in working on listed buildings. You can see a selected list of some of IQ's past listed building projects below.

Tips for adding extensions to listed homes

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.

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.

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 of knowledge in complex projects of this nature.

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

Bespoke Glazing in Listed Buildings