Regulations regarding double glazing for Grade I and II listed buildings

A window in time – why do listed windows matter?

When you look at any property, the windows are among the most noticeable features. For listed buildings, they’re particularly distinct. Listed windows help tell the story of a building’s history and form an important part of its aesthetic appeal. As such, they fall under the core features that make your home historically and architecturally significant (which is why your home is listed in the first place), so it’s not always possible to replace them.

The good news is that when you’re seeking a more thermally efficient or secure home, or you simply need to repair a historic window, you do have there are options. Historic England is the public body responsible for protecting England’s heritage buildings and environment. They offer detailed guidance on the circumstances and considerations that should be considered when looking to renovate the windows in a Grade I or Grade II listed property. Specifically, they address whether double glazing is a realistic option or whether heritage secondary glazing is your best course of action.

Double glazing for listed buildings

Double glazing is the most secure option for a new window, and it can be up to twice as effective at reducing heat loss as secondary glazing. However, the panes are thicker and heavier – which often means they’re simply not suitable for a listed home. The following factors will have a bearing on whether you’re likely to gain consent to install double glazing:

The size of your window frames

As a rule, a double-glazed window is anywhere between 22 and 28mm thick, compared to a traditional single-glazed window that sits at just 2-3mm thick. As a result, you may find your listed window frame and glazing bars are unable to cope with the size and weight of double glazing.

In recent years, slimline double-glazing units have grown in popularity. These are just 16-18mm thick. While they can still be too heavy for some traditional windows, they may be a good solution if your glazing rebates are strong and deep enough without the need for alteration. A good example is a single casement window or a Victorian sash window.

Previous window replacements

If your windows have previously been replaced by something less sympathetic to the history and style of your home by a past owner, you may be in a better position to install double glazing – and these slimline options can work well. They offer a thermally efficient and secure window, while also providing an opportunity to install windows that better suit the historical look of your home – helping to restore some of its character.

If previous window replacements are already designed in keeping with the history of your listed home, they may be able to accommodate double glazing depending on their shape and size.

The materials your windows are made from

Some listed buildings have steel windows. If this is the case for your home, you may find that your steel frames are strong enough to be able to hold slim double-glazing units.

However, if your windows still hold original glass, or any unusual features such as stained glass, you may find it much harder to obtain consent for double glazing. Single glazing and double glazing have different reflective qualities to start with – but traditional glass panes in themselves have a distinct look to them, with unique irregularities and their own reflective quality that modern flat glass simply does not replicate.

If the glass has already been changed to something less unique by a previous owner and there’s no significant historical glass left in the window already, you’re more likely to be able to install double glazing.

General guidance for listed building window replacement

Everything about the architecture of your listed home matters. Special period features in your windows, such as stained glass or even the irregularity of older glass, make up part of that character – which is why replacing them in some cases is just not possible. While there’s flexibility to encapsulate these features into a new design if a window is beyond repair, the general guidance is always to maintain the features of your home in good condition and repair when needed. This is generally better than opting for window replacement – which can be complex, costly, and not easy to obtain consent.

It’s also worth considering the impact listed building window replacement has on the overall value of your house. In part, the value of your listed home is derived from its historical authenticity, period features and individual character. Secondary glazing rarely affects this, but double glazing might. With the high price of double glazing and the decades it can take to recover that cost, you might find that secondary glazing is not only more appropriate for your listed building but makes more financial sense too.

Additional considerations when making alterations to listed buildings

As ever with your listed home, any alteration you plan to make will need Listed Building Consent if there’s a chance it will affect the character and historical significance of the property. This is required by law and making any unauthorised changes could result in a fine or even a court case – so it’s important that you familiarise yourself with the consent application process and, if possible, get to know your local conservation officer too. This will always help streamline the process when planning any changes to your home.

It’s also worthwhile factoring in the specialist skills and materials that are likely to be needed when altering or repairing your listed property. Any works should use the same materials from which your home is built – from timber to cob to wattle and daub – and tradespeople specialising in these more niche techniques will be in higher demand. Your timelines and budget may be impacted, but it’s always worth the little extra effort in the end.

In the same way, the insurance you need for a listed property is more specialist too. Listed property insurance for graded buildings includes the unique characteristics, period features and skilled building techniques that make your home nationally significant. It also considers the higher risks associated with older buildings, from fire to water damage. Provided by specialists with in-depth knowledge of listed buildings, the right listed property insurance gives you the peace of mind that if anything happens to your treasured home, you have the proper protection in place.

At Abode, we focus exclusively on insuring listed and heritage buildings, so we understand the extra care they need. To find out more and have a friendly yet expert chat, get in touch to talk about your listed property.