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A Guide to Replacing Windows in a Conservation Area

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A listed building in a conservation area where replacement windows must be approved by the local planning authority

A Guide to Replacing Windows in a Conservation Area

Reading Time: 8 Minutes
Published on: June 19th, 2020

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Window replacement in a conservation area

Replacing windows in a conservation area isn’t straightforward. Windows aren’t just bits of glass to plug the holes in your walls and let the light in, they are one of the defining features of a building and one of the focal characteristics. Fitting the right or wrong style of windows and greatly enhance or completely ruin the look of a building, and this is very important in conservation areas or in Listed buildings.

What is a Conservation Area?

According to Historic England a conservation areas 

“… exist to manage and protect the special architectural and historic interest of a place”.

Basically, conservation areas are there to protect and retain the characteristics of a unique area of historical significance. 

There are over 10,000 conservation areas in England and every local authority has at least one in it’s care. Conservation areas have extra planning controls and considerations attached to them to protect the historical and architectural elements that invoked the designation in the first place.

Why do we have conservation areas?

A good example of why we have conservation areas is the town of Berwick on Tweed, whose conservation area includes the defending wall built in Elizabethan times to repel invaders from Scotland. Having the place designated a conservation area stops anyone from developing a modern building that is out of character with the rest of the town, or altering existing structures so that they don’t match their surroundings. 

Whilst Berwick on Tweed will never look as it did in Elizabethan times, it’s important to retain the characteristics of the place so we get the impression that we are in an ancient and auspicious area. When we modernise historic buildings, we destroy some of the character of England. Conservation areas are there to make sure we don’t.

Photo of conservation area Berwick on Tweed showing the Elizabethan wall
Photo of conservation area Berwick on Tweed showing the Elizabethan wall

Article 4 Direction

The designation of a conservation area is officially referred to as ‘Article 4 Direction’. The direction allows local authorities to ‘withdraw specified permitted development rights across a defined area’.

According to the Government website an Article 4 Direction can:

  • Be any size from a specific site to an entire local authority-wide area
  • Remove specified development rights regarding change of use or operational development
  • Remove permitted development rights with temporary or permanent effect

More information about Article 4 Direction can be found on the .gov website here

Listed Buildings

A listed building is an individual building of ‘architectural or historical interest’. Not all buildings in conservation areas are listed, and a building is designated as Listed based on its own merits. Therefore a listed building could be inside a conservation area or anywhere else. Listed Buildings are either designated as I (one) or II (two). There is a level between these – Grade II*.

  • Grade I: buildings of exceptional interest.
  • Grade II*: particularly important buildings of more than special interest.
  • Grade II: buildings that are of special interest, warranting every effort to preserve them

Planning Permission

Planning permission is needed for alterations to all buildings, however Listed Buildings and Conservation Areas require special permission.

You will need planning permission for all work that affects the characteristics of a building, including demolition, extensions and alterations. This particularly applies to Listed Buildings, where you must apply for Listed Building Consent.

Some local authorities apply special control in conservation areas, specifically noting building features such as doors and windows.

Unauthorised work is a criminal offence

In short, whether your building is a listed building or it’s in a conservation area, you will need planning permission to repair or replace your windows. Remember – unauthorised work is a criminal offence, with prison sentences given to the worst offenders. The best case if you carry out work without permission is that you will have to pay a fine and pay again to make the alterations you have made compliant. However much you may dislike dealing with Government agencies, it’s cheaper, faster and less stressful to go down the proper path and get planning permission before you do anything else.

To find out what planning permissions you may need, visit the Government’s Planning Portal website:

Should I Repair or Replace my Windows?

Local Authorities prefer repair rather than replacement of windows. Specifically, windows of historical interest should be made good with an accurate like for like repair carefully matched to the original item. Like for like repairs do not require planning permission in conservation areas or in Listed Buildings. Altering or replacing windows does require planning permission.

A rotted wooded window in a conservation area in need of replacement

Image courtesy of

Double Glazing in Historic Windows

One of the defining features of historic windows is that they only have single glazing. By definition single pane windows are less efficient than their modern counterparts, and the age of the windows will mean they are probably leaky, draughty and noisy too. This is sometimes overcome with the stop-gap solution of installing a second window on the inside. These do little to improve the performance of historic windows but it’s better than nothing.

When to replace historic windows

Sometimes it does become necessary to replace historic windows. The replacements should be as similar as possible to the original windows. If the windows to be replaced aren’t the original items and are non-historic in design, then they should be replaced with new windows that match the original windows as much as possible.

What are the characteristics of an historic window?


A window may still contain the original glass. Glass production has changed considerably in the last 150 years, any panes from before the mid 1800s will be hand made. These panes will be thin and contain imperfections that add to the beauty of them, but they are very fragile. Any panes that have survived the rigours of time will be quite valuable – if you are replacing historic windows, be careful when removing them, they could be worth some money!

Older windows are made from smaller panes of glass – usually 4 or 6 held together with smaller vertical and horizontal strips of wood. This is where the stereotypical ‘olde worlde’ look comes from. After the middle if the 19th Century glass production made huge advances and larger, stronger panes of glass could be mass produced.


The style of the frames is another defining feature of a building and can be used to date a structure. Older windows were hand made and, surprisingly, made of much more durable timber than generally used today. This is due to the timber coming from temperate climates where trees grow at a much slower pace and tend to be denser as a result. There are superior timbers available today such as Accoya® and Red Grandis, but sadly the majority of modern windows are either plastic or quick-grown softwood with a short lifespan (not to mention the ugliness of the design!).

As glass and window making technology improved, it was possible to have much bigger windows. Bigger windows required stronger frames, so, as an example,  we see the introduction of ‘horned’ sash windows. The horn makes for a much stronger joint. A modern reproduction window would have a horn although it would be purely aesthetic as modern frames are far stronger and more durable than their forebears.

Modern Improvements when replacing historic windows

When windows are beyond repair, or replacement is necessary for other considerations such as energy efficiency or security, there are many options available. There are companies that produce heritage windows from both timber and uPVC that pass local planning authority guidelines.

When replacing your historic windows it’s advisable to use a company who specialise in heritage windows. They will be familiar with the process of getting plans passed by the local officer, and their products will have been developed for Listed Buildings and conservation areas. The experience they have will be invaluable to your project, and the fact that their products have already been approved for use numerous times by local authorities means that permission will be more likely to be given and it will speed the process up no end.

Double Glazed Heritage Windows

The main improvement when upgrading historic windows is to include double glazing. The benefits are obvious and have been covered numerous times on our blog. The main issue with installing double glazing in these situations is that the gap between the panes is visible and so is the second pane. The effect is called the ‘double shadow’ or ‘double reflection’ effect, and windows like these will tend not to be passed by local authority planning officers.

Often people try to promote is slim double glazing – a narrower gap filled with Krypton or Xenon gas to improve the efficiency of the panes. There is a problem with slim double glazing in that the seals can be too slim to hold the required amount of sealant or dessicant and, as a result, they have a history of failure after only a short period of time. For more information on this, refer to our blog called The Problem with Slim Double Glazing.

close up of astragals on spacia vacuum double glazing a perfect replacement window in a conservation area

Close up of astragals on SpaciaTM vacuum double glazing a perfect replacement window in a conservation area

More recently Vacuum glass is being used in heritage windows, to great effect. Developed in the earthquake areas of Japan to be lighter than conventional double glazing, vacuum glass is perfect for heritage projects because it’s the closest efficient alternative to the original single glazed panes. With a barely perceptible gap of only 0.2mm the vacuum cavity makes a highly efficient insulation and soundproof barrier. The Georgian look of older windows – windows made up of smaller panes held together with those horizontal and vertical strips of wood – is replicated with faux bars to maintain the illusion of being a much older window. Pilkington are pioneers of vacuum glass with their award winning Spacia™ range, currently only available from a handful of expert suppliers (Note: Gowercroft are one of them, just saying!).


As mentioned earlier, whilst many manufacturers use either plastic or inferior, cheap timber, there are some very effective timbers available. There are some excellent, and highly sustainable, South American and Asian hardwood varieties, all of which will extend the lifespan of your windows. There are also some modified timbers such as Accoya®  which will even further extend the service life of the units.

These materials are good for building window for 2 reasons:

  • Their extended durability – they will be much more resistant to insect and fungal attack
  • Their stability – they won’t expand or contract as much as other materials.

The stability is important – it puts the protective layers of paint or varnish under less strain. On less stable timbers, the constant contraction and expansion eventually leads to cracks in the coating, allowing water to penetrate and accelerate the rate of damage and decay.

Manufacturing processes also play a major role in the length of service life of windows. Precisely fitting windows with strong, inflexible joints will last much longer that loosely or too tightly fitting windows with insecure joints that allow movement to again further accelerate the rate of deterioration. 

In Conclusion

To recap when replacing windows in a conservation area or listed building:

  • Find out what planning permission you need
  • Apply for planning permission well in advance
  • Partner with a manufacturer with a proven history of heritage window production and installation

If you are in need of help when replacing windows in a conservation area, the team at Gowercroft are well versed in the ins and outs of obtaining the correct planning permission and will gladly help you through every stage of your project to make sure it runs smoothly.