Leaded windows double glazing retrofitting

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Leaded windows double glazing retrofitting

Leaded windows that are single-glazed with lead on the outside can now be retrofitted with double-glazing.

Using the latest double glazing technology, 7 mm vacuum-sealed FINEO glass, we can transform your leaded windows.

We must employ slightly different techniques than we usually do when retrofitting double glazing into sash windows, though. 

As you might already know, with vacuum-sealed double glazing, unlike with single glazing, condensation forms outside the windows, which is an indication of good quality insulation.

However, if we retrofit the original window and place the lead stripes outside the glass where condensation will form (which is usually how we retrofit double glazing), there is a high chance that the lead will peel off over time. 

vacuum-sealed window

For this reason, the only way to add double glazing and preserve the old window style is to add a second pane of glass behind the old glass (which is secondary glazing) or add it in front of the old glass.

Secondary glazing is a very conservative option that has been on the market for a while.

Secondary glazing for leaded windows

Secondary glazing has some disadvantages that we have covered in a previous article as well as major advantages, like that it can be installed in listed buildings.

Secondary glazing installation also does not require permission from a conservation officer.

This is because secondary glazing doesn’t interfere with what is already in place, and it doesn’t harm or change the structure of the window of the building.

Install double glazing in front of the leaded window

The option to install the double glazing in front of the leaded glass will work well for non-listed buildings with mixed styles of windows in one property, where some windows are leaded and some are not.

This method will also work better on smaller casements rather than on larger ones. 

mixed styles of windows

To add the double glazing onto the exterior side of the window, you are looking at an additional 10mm thin frame that will sit in front of the leaded single glass window and hold the double glazing.

This additional frame isn’t noticeable from afar. Your windows will look as they always have.

Retrofitting double glazing windows


Currently, secondary glazing is the best option for leaded windows in Grade 2 listed buildings or large leaded windows.

If we find new products, techniques or technology, we may hit on the solution to glue the lead to the glass so it does not peel off in a couple of years when condensation is formed outside; we will add a new article to our blog.

If you want to retrofit double glazing into your regular single glazed sash windows or leaded cottage windows or just simply repair sash windows, contact us.

There is a good chance we can make your original windows as efficient as modern.

Benefits of retrofitting leaded windows with double glazing?

  • Efficiency – By adding an additional layer of glass to your windows, you can reduce the amount of heat loss in your home by up to 18%, saving you money and energy.
  • Reduce external noise – If road noise is an issue for you, double glazing can reduce noise by up to 31 decibels.
  • Reduce UV – Single pane windows can let in a lot of UV light which can damage your art, paint, soft furnishings, and more. Double glazing can stop up to 97% of UV rays from entering your home.
  • Solar control – If your home is unbearable in summer, having double glazing can massively reduce how much heat can enter your home during the hottest parts of the year. Double glazing lock heat in your home but keeps the heat outside from entering.

Are leaded windows old-fashioned? 

Leaded windows are certainly historical but not old-fashioned.

There are companies making uPVC versions of leaded windows right now.

They don’t have the charm or the style of the leaded windows on your home, though, as they are entirely made from plastic. However, the style is still very much in fashion.

While window styles change over the years, the great styles will always be in fashion, and leaded windows are regarded as one of the most beautiful and iconic windows in the UK. 

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