Listed Buildings and Glazing

Tower Vaults, London. Structural Frameless Glass Extension on Listed Building

When you decide to renovate or expand a listed building, it can seem like an overwhelming job. Surprisingly, there are no set rules for extending or renovating a listed building in the UK and the decision can easily come down to the whims of the local conservation office.

What is a Listed Building?

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 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.

What are the different Listed Building grades?

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 and of are of historical significance. Any building under the age of 30 is not listed.

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.

Why retain Historic Glazing?

Windows are not just great for providing a natural source of light, they also add character and style to the exterior of a building. 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.

I would like to have my historic windows replaced, how would I go about doing this?

To protect the character and appearance of a listed building, different planning rules are put in place. When making any alterations or replacements to a listed building these must be carefully considered. During the planning process, we highly recommend that you seek the advice of a skilled technician or your local conservation officer who will be able to provide advice and the likely hood of the proposed planning permission being granted.

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.

Structural Glass or Glass Box Extensions

To ensure the design integrity of the original building is clear, English Heritage often supports a more contemporary approach to extending listed buildings. Using structural glass or glass box extensions is a great way to achieve this and leave a clear definition of the classic building scheme.

IQ Glass recently worked on a project in Central London on a Grade 1 listed building just up the banks from Tower Bridge. The 16th Century Security Cabin is now housing a well-known coffee house chain who wanted to extend their space with a completely transparent finish.

Using a full Structural Glass extension with 5m long glass beams, our Structural Designers worked diligently to ensure all supports and links to the original building were sound, whilst creating a streamlined finish. All supports for the glass beams and fins were designed as hinge supports to avoid a moment on the existing structure.

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 modern glass box is separated from the traditional glass box extension. 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.

The use of Low Iron Glass and Anti-Reflective Glass

The necessary framework can be kept to a minimum by using low iron glass as it barely interrupts the view of the outside. There is no green tint visible providing much clearer transparency to the glass. This allows the glass to unobtrusively integrate with the original stunning design of the heritage building. An anti-reflective coating on the glass can also help to reduce the potential reflection by up to 1%, helping to provide an unobstructed and clear view from both sides with a light transmission of up to 98% with high durability and resistance to scratch. This is less visually intrusive and provides a lovely aesthetic to the original design of the listed building.

Blenheim Palace in Oxfordshire is a world heritage site boasting a long history and is very important to British history. This project included architectural minimal glazing which IQ helped design and install, bearing in mind the stonework and design of the building we specialised fixing technique to keep the original design protected. Low iron glass was used throughout the architectural glazing to ensure the glass appeared ‘invisible’. This creates a transparent, clear and neutral effect providing a lovely effect to this building. An anti-reflective coating was also applied offering ultra-clear and non-reflective glazing no matter the levels of light.

Mondrian® Windows

IQ offer Mondrian® windows as a replacement for the current steel windows on listed buildings to help retain the traditional steel effect. All windows from our steel fabrication factory are individually designed and made to precise measurements. Mondrian® windows utilise a traditional window design with a steel frame width as little as 47mm. We also have a wide variety of finishing options available, such as galvanised steel, corten steel, patinated bronze or stainless steel to provide a unique and beautiful finish to your steel windows, whilst retaining the traditional look of the building.

With an in-house Structural Engineering team, IQ Glass has worked on a number of listed buildings and properties in the UK and can fully support your structural glass design.

If you would like any further advice then please do not hesitate to call us on 01494 722880

or email us at

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