Sash Windows London

Yes, you certainly can have timber double glazed sash windows. Modern sashes are able to accommodate thicker double glazing, making windows thermally efficient and offering greater soundproofing. Double glazing is the perfect way to bring beautiful, traditional sash windows up to date, without losing their charm.

For many people, the mention of sash windows conjures up the image of a rickety, wobbly, ill-fitting Victorian window that lets in constant draughts. Unfortunately, this is often the experience of people who have older sash windows installed in their homes, which haven’t been upgraded or received proper maintenance for many years. The good news is, it doesn’t have to be this way. Modern wooden sash windows and double glazing can transform your home and way of life, allowing you to enjoy a warmer, more comfortable, draught-proof home.

Double glazed sash windows – your questions answered           

Many of our customers have questions about timber double glazed sash windows and want to know more about the process and the possibilities. To help give you a good starting point, we have put together some answers to the questions we are most frequently asked about sash windows and double glazing.

The ins and outs of wooden double glazed sash windows

Q1: What exactly is double glazing? How does it work?

It is simply glazing that is made up of two panes of glass fitted into the same unit. The panes will have gas between them, usually argon. This helps to keep warm air in and cold air out. Did you know that in a badly insulated room, all the air inside will be changed three times every hour? This means you are continually heating air that is almost immediately lost. Double glazed sash windows can help enormously.

Q2: Can all sash windows now be double glazed?

If you have new sash windows installed, then they can be double glazed. We make all our wooden sash windows by hand, crafting them in our workshop and fitting the glass ourselves, so we can ensure double glazing can be accommodated. There may be some planning restrictions – see the next answer for further information.

Q3: What about planning permission? Will I be allowed to install double glazed sash windows?

If you live in a house that isn’t in a conservation area and there aren’t any other regulations that apply, you generally won’t need planning permission to install new windows.

If you have a house in a conservation area, you might possibly need planning permission. The same goes for flats – they don’t have any permitted development rights, so you may need planning permission depending on your local authority’s stance. Some councils in London can be quite strict but will usually be happy to let you proceed if you are replacing windows like for like.

Listed buildings are more complex and you won’t usually be able to get planning permission for double glazed sash windows, unless you can prove that your existing sashes are beyond repair. It might be an option to install secondary glazing instead.

Q4: How long will double glazed sash windows last?

This depends on how well you maintain your windows. We offer wooden double glazed sash windows made of the highest quality materials, that are designed to last. They could easily last for 20 years or more if well looked after.

Q5: Will the double glazing make the windows look any different?

There will be very little difference in terms of appearance – unless you want to opt for a different look, of course. The frames themselves will remain the same thickness as the originals but there will be slight differences in the moulding on the inside and on the outside bead. We will make new windows or window sashes by hand so we can ensure they are the perfect fit for your property, retaining the period features and designs that make your windows beautiful.

Installing double glazed sash windows in the UK

Q6: What kind of energy efficiency can I expect from my double glazed sash windows?

Modern double glazing is highly energy efficient. The overall energy efficiency rating of your home will depend on a number of factors, such as the presence of insulation in the walls and loft, the heating systems installed (i.e. gas central heating, electric central heating, storage heaters, or other methods of heating a home) and the roofing material. However, the windows are a key factor in the overall energy efficiency rating of a house and double glazing could help save you hundreds of pounds a year.

Q7: Are there any other kinds of glass I can have?

You can also choose acoustic glass and safety glass for your sash windows.

  • Acoustic glass: 8mm acoustic glass / 12mm argon gas filled warm edge spacer bar/4mm clear glass = 24.8mm acoustic double glazed unit. 1mm of acoustic glass will reduce noise by 1 Decibel, making it highly efficient. This is a popular addition for London properties.
  • Safety glass: choose laminated glass or toughened glass for extra safety if the glass is broken. It won’t shatter in the same way as normal glass would, making it popular for public buildings and properties on busy streets, on the ground floor.

Q8: How much do double glazed sash windows cost?

It is very difficult to give costs for double glazed sash windows without know exactly what you require. It will depend on so many different factors, like the size and shape of your windows, the number of panes of glass, and the glass specifications you choose. It will also depend on whether you choose to replace your whole window including the box frame or have new double glazed sashes only. We offer quotations free of charge and there is no obligation to go ahead.

Q9: Can you fit double glazing into my existing sash window?

No – this would be very difficult to do. Older sashes simply weren’t designed to accommodate double glazing and the glazing bars usually aren’t deep enough to hold thicker panes in place. You can choose double glazing when you have complete new box sash windows installed or, if you don’t want to replace your entire window box, we can install new double glazed sashes into the existing box frame. This requires less work and we will make a sash in our workshop to match with your existing box frame, so your windows will look the same – but without any cracks, damage to the timber, and with brand new double glazing!

Q10: Is there anything else I can do to improve the energy efficiency of my sash windows?

It is recommended that you maintain your sash windows on a regular basis to keep them in top condition. This will involve draught proofing windows, replacing beads and installing weatherproof seals to make them airtight. However, this will make very little difference if the windows themselves are not energy efficient – heat will escape rapidly if frames are old and there are gaps elsewhere, or the glass is thin. To maximise energy efficiency, double glazing will be the most reliable option. This can then be maintained to keep it functioning efficiently well into the future.

Talk to us about wooden double glazed sash windows

Interested in wooden double glazed sash windows? Why not ask us for a free quote? We can discuss your options in detail, and there’s no obligation to go ahead. Call 020 3582 7621 or fill in our contact form and we will be in touch to talk about your sash windows.

Contact the Wandsworth Sash Windows team

Talk to us – we can help with your bespoke window, door and joinery requirements. Call 02079247303 or email