Everything You Need to Know About Double Glazing Existing Sash Windows

For homeowners living in period properties, comfort and preservation often go hand in hand. Original timber sash windows are a defining feature of London’s Georgian, Victorian, and Edwardian architecture, but they can sometimes fall short when it comes to modern insulation standards. The good news? You don’t have to choose between character and comfort. At Mortice & Green, we specialise in double glazing existing sash windows, allowing you to retain your home’s heritage charm while significantly improving energy performance.

Here’s everything you need to know about this effective and sympathetic upgrade.

Can You Really Double Glaze Existing Sash Windows?

Yes, in many cases you can. Rather than replacing your original windows entirely, our skilled joiners can carefully remove the existing single-glazed sashes and retrofit them with new double glazed units, while keeping the original box frames in place. This approach is ideal for homeowners who want to improve insulation without losing the authenticity of their property’s windows.

We also offer the option of manufacturing bespoke hardwood sashes that match the period design exactly, fitted with slimline double glazed units for a seamless finish.

Benefits of Double Glazing Your Existing Sash Windows

1. Improved Energy Efficiency
Double glazing significantly reduces heat loss through the glass, helping to keep your home warmer in winter and cooler in summer. This can lead to lower energy bills and a more comfortable indoor environment year-round.

2. Noise Reduction
Living in London often means dealing with street noise. Double glazed sash windows help reduce outside sound, making your home a quieter and more peaceful place to live.

3. Reduced Draughts and Rattles
As part of our double glazing upgrade, we also offer integrated sash window draught proofing, which stops cold air infiltration and eliminates rattling, common issues in older sash windows.

4. Retained Aesthetic Appeal
With Mortice & Green, all sashes are refurbished or replicated to match the original design, using traditional joinery techniques. You keep the period look, just with modern performance.

5. Increased Property Value
Original features that have been thoughtfully upgraded often appeal to buyers. Double glazed timber sash windows offer the best of both worlds: heritage style and modern efficiency.

Is This Suitable for Conservation Areas?

Yes, in most cases, but it’s important to proceed with care. Many conservation areas support the sympathetic upgrading of sash windows, provided the original appearance is preserved. Our bespoke double glazed units are specifically designed to look like traditional single glazing, meeting the visual requirements of listed and conservation properties.

We’ll guide you through the process and help with any planning permissions or building regulations if required.

What If My Windows Are in Poor Condition?

Even if your sash windows are suffering from rot, broken cords, or general deterioration, that doesn’t mean they need replacing. Our team can carry out comprehensive sash window refurbishment, including timber repairs, rebalancing, and hardware replacement, before installing your double glazing.

Alternatively, we can manufacture entirely new hardwood sash windows to replicate the originals, fitted with discreet double glazed units for maximum efficiency.

Trust Mortice & Green for a Seamless Upgrade

With over 30 years of experience, Mortice & Green are London’s trusted specialists in sash window repair, refurbishment, and replacement. Our approach to double glazing existing sash windows combines traditional craftsmanship with modern performance, helping you enhance your home without compromising on its original character.

Whether you’re looking to improve warmth, reduce noise, or futureproof your property, we’re here to help. Get in touch today for a no-obligation quote and expert advice personalised to your home.