Double Glazing for Listed Buildings
Renovating a listed building or a property in a conservation area can prove to be something of a headache. English Heritage maintains a raft of rules and regulations regarding these types of buildings, and although they are there to protect areas of outstanding beauty and tradition, they can be highly frustrating when trying to improve these properties.
As a general rule, double glazed windows are not allowed in grade I or grade II listed buildings, although there have been cases where it has been allowed, so each property needs to be treated individually. This is likely to mean much correspondence and dialogue between home owner and local authority.
Unfortunately if you have taken on a listed building this comes with the territory. Repairing the original windows and using secondary glazing is the preferred method as far as English Heritage are concerned, and this is allowed in Grade II buildings. However, secondary glazing is nowhere near as efficient as double glazing when it comes to energy saving and noise reduction.
Are there any exceptions or restrictions?
As stated, each case must be considered on an individual basis. The planning office will want you to repair the windows if possible in the first instance. If this is not plausible, then like-for-like replacement will be the next best option, and re-using materials or finding local suppliers to use exactly matching materials will please the regulators.
It is beyond doubt that it would not be acceptable to install plastic double glazed windows into a listed property, so if you are sure that you want to try and persuade the planners to allow you to install double glazing, you may need to have bespoke frames made that exactly match the original style so as not to change the outer appearance of the property.
Grade III buildings have slightly more relaxed regulations, and local authorities may be able to approve certain changes, and give planning consent without consulting English Heritage. For properties in a conservation area, you must apply for conservation area planning permission. This requires you to replace windows with ones that look and operate the same.
Regulations do allow you to use any material, and do not insist on using the original materials, however, in practice it is often difficult to find suitable replacements that have been made with modern manufacturing methods.
Are there products designed especially for listed buildings?
Anyone aiming to install double glazing into a listed building would almost certainly need to have frames and windows specifically designed for them. As it is important to retain the historic fabric of the building, the new windows would need to be indistinguishable from the originals.
One such example would be Orchard Farm in Pitstone, Buckinghamshire. This Georgian house is listed as grade II, and owners Robert and Susan Groves fought a long battle to get planning permission to have double glazed windows installed in nine of the windows, including five to the front of the property.
Aylesbury Vale council’s policy on replacing windows is in line with that of English Heritage; that the originals should be restored and secondary glazing should be installed. Eventually the council planners agreed that the Groves’ could install double glazing and they had timber framed bespoke units made which replaced the originals, first installed in the 1900’s.
The manufacturers of the windows, the Box Sash Window Company, reduced the glazing bars down to 19mm wide, and say they were able to produce the double glazed units to be almost identical to the original windows.
The case highlights a real issue with regard to listed and protected buildings. While it is important to retain the history and fabric of these properties, for them to survive someone must be living in them and maintaining them. As energy efficiency is so important in today’s society, it is essential that a balance and a compromise can be made between retaining original features and making the houses comfortable and habitable for their owners.
What about secondary double glazing?
Secondary glazing is one way around the conundrum for listed buildings although it is worth noting that grade I buildings are also subject to regulations governing changes to the interior as well as the exterior. Secondary glazing consists of installing an inner window directly behind the original frame to achieve a double glazed window of sorts.
It is not considered as energy efficient as a sealed unit, nor will it provide the same level of noise reduction. It does however improve upon the thermal insulation of single glazing. Permission is still likely to be required for secondary glazing, so it is still important to contact the local authorities, but in most cases it is likely to be granted.
The energy saving trust estimates that secondary glazing is about half as efficient as double glazing. This is something to consider if you are renovating a listed building; if there is a possibility that English Heritage and local planners will grant approval for double glazing, it is worth pursuing.
Listed buildings and properties in conservation areas are subject to a variety of regulations governed by English Heritage, and local planning authorities. The most high profile of applications may even go before the Secretary of State for the Environment, Transport and the Regions for a final seal of approval. If you are renovating such a property, or considering buying one, you should familiarise yourself with the legislation in your particular area as well as the regulations in general.
In the majority of cases councils tend to follow the policy of English Heritage, who recommend that the original frames and windows be restored using the original materials to maintain the historical integrity of the building. Usually they would allow secondary glazing to be fitted directly behind the existing window to provide a form of double glazing although this may be excluded in grade I buildings.
Grade I properties are subject to regulations covering every part of the property, including the interior, and even the smallest of changes may require planning permission.