Will double glazing old windows strip them of their character and charm – or are there ways to do it sympathetically? I asked the pros how best to tackle it

It is often the original features that draw people to older properties, lending them character and charm that can be lacking in modern houses. Windows, in particular, are one of those elements of any home that will make or break its kerb appeal – all too often, original windows get replaced or updated in a totally unsympathetic way.

Many people don't realise that it isn't just the frame style and material that contributes to the look of a window, but the types of glazing used within them too. It is understandable to want to select glazing that will reduce heat loss, but when it comes to older windows, homeowners can find it hard to pinpoint the right solution.

If you are considering double glazing old windows but are unsure how this will affect their appearance – or if it is even possible – this guide is for you guide. As an experienced renovator and owner of an old house myself, I explain the pros and cons of making this upgrade and what the job entails.

Can you double glaze old windows?

If you are living in or renovating a period property that has its original windows in place, they may well be fitted with single glazing. While this type of glazing has a certain beauty about it, with its slight imperfections and rippling, it is not always the most comfortable to live with.

'Single glazing is one of the biggest sources of heat loss in homes,' reveals Becky Lane, CEO of home energy upgrade company Furbnow.

Terry Hill, MD at KLG Rutland, shares some other benefits of replacement glazing. 'Upgrading your period home’s windows and doors with modern replacements brings a host of long-term benefits including, improved energy efficiency, better security, reduced maintenance and possibly noise reduction,' he says.

While you can, in theory, fit double glazing into some older windows, is upgrading from single to double glazing always such a good idea?

'Sometimes the frames simply cannot handle it as many older timber sash and casement windows were not designed to withstand the weight or thickness of modern sealed systems,' warns Andrew Haydon, director at Simply Plastics.

Becky Lane

Becky Lane is the co-founder and CEO of Furbnow, leading the company cutting through the home energy upgrade chaos with clear plans, simple tech and real experts. With more than 15 years’ experience in home energy, and as a qualified Retrofit Coordinator, she brings both technical insight and hands-on experience from working with households, councils and industry.

Andrew Haydon

Andrew Haydon is a DIY and home improvement expert at Simply Plastics, where he helps homeowners create practical, affordable upgrades using durable, energy-efficient materials. With hands-on experience spanning everything from garden structures to glazing and window insulation, Andrew specialises in simple, low-cost ways to make homes more comfortable and energy smart all year round.

Will double glazing old windows ruin their character?

Even if, after investigating whether or not the frames of your old windows are up to the job of carrying the weight of double glazing (something a skilled joiner should be able to advise you on) you find you can go ahead with the task, there is still the small matter of appearance. In short, will switching out your single glazing for double in a bid to make an old house warmer spoil the look of your windows?

'Double glazing older types of windows does make sense in some homes, but it may not always be the best option, particularly if the original joinery and detailing are still present and if the window proportions, glazing bars, and traditional putty lines are contributing to both the exterior and interior of the property,' explains Andrew Haydon.

'Retrofitting double glazing can disrupt glazing bars, sightlines, and frame proportions, which often takes away from the original appearance, especially where fine details are part of a window’s character rather than decoration alone.'

What are the alternatives to double glazing for older homes?

If your windows are not suitable for double glazing, or you have come to the conclusion that adding double glazed units would ruin their character, you still have options that can help keep your house feel warmer and reduce your energy bills.

'A better alternative in these cases is secondary glazing, which allows you to keep the original window precisely as it is,' says Andrew Haydon. 'This method works by installing a separate pane on the internal side of the existing window, often fitted into its own narrow frame.

'When installed internally, secondary glazing keeps the original window intact and fully functional for ventilation, cleaning, and later repairs,' continues Andrew. 'This allows you to perform routine maintenance without interruption, remove panels during the warmer months if necessary, and still reach the original glass without the need for specialised tools. It also helps reduce draughts, which in turn limits heat loss and lowers energy use by preventing heating systems from working harder than necessary – in fact, it can even enhance daily comfort to a level that is comparable to double glazing.

'And, finally, because of the larger air gap between panes, sound control is improved so it’s also frequently used in residences close to busy roads, train lines, or town centres. When combined with draught-proofing and some basic repairs, rooms will feel warmer, quieter, and have less condensation without replacing or ruining windows that still have many years of use left.'

Is it better to replace old windows rather than upgrade the glazing?

There are cases where original windows will just be in too bad a condition to make restoration a viable option. In these cases replacement windows will be needed but this should only really be a last resort and needs to be done with great care – changing windows can, in some cases, totally strip a period house of its character. This will also usually be a more expensive route.

That said, if you take the time to research the options and find a joiner who can match the originals, replacement doesn't have to be a disaster.

'Replacing windows or doors in a period property doesn’t mean losing its soul,' reassures Terry Hill. 'With a sympathetic design such as heritage ranges, flush sash or modernised vertical sliding windows and professional installation, you can preserve your home’s historic charm and character while enjoying the comfort, efficiency and security of modern living.’

FAQs

Do you need planning permission to double glaze old windows?

Whether or not you will require planning permission to upgrade your windows very much depends on your house and the area you live in. In many cases, there will be no need to apply.

However, if you live in a listed building, you will almost certainly require listed building consent in order to make any changes. Additionally, if your house is located in a conservation area, you may also need to seek permission.

'If your home is listed or within a conservation area, certain restrictions may apply to how windows and doors can be replaced,' explains Terry Hill. 'Reputable installers should work closely with homeowners, local authorities and heritage officers to ensure compliance with conservation area regulations, listed building consent and building regulations for energy efficiency, ventilation and safety.'

'If you have a Victorian or period home these often have architectural features protected by heritage conservation rules,' picks up Becky Lane. 'You will need to work with conservation officers and heritage experts to choose a solution that preserves the character of the house – and consider reversible techniques that can be easily undone if necessary.'

If your home already has double glazed windows, or you are adding an extension, you might well be looking into double vs triple glazing. It is well worth checking out the pros and cons of each before making a decision as, in certain cases, making what can be an expensive swap won't be worth it.