Sash windows double glazing

Retrofitting double glazing to wooden windows can improve energy efficiency, increase comfort and reduce energy bills.

Sash windows double glazing

Can existing single-glazed sash windows be double-glazed?

Absolutely, original sash windows in historic properties can now be upgraded with slim-profile double-glazing units. This ensures that such unique windows keep their charm while providing the convenience of energy efficiency.

The reglazing of the original windows can improve their energy efficiency to match the performance of modern A-rated windows.

sash windows repair in braintree

Retrofitting Double Glazing To Wooden Windows

1. Remove existing single glazing

2. Retrofit new slim-profile vacuum glazing into existing sashes

3. Change cords and add additional weights to counterbalance the additional weight of the new heavier glass. Service pulleys and add new cords.

4. Draft proof the existing sashes

In most period properties, original sash windows still have single-pane glazing installed. Single-glazed windows are not energy efficient; as a consequence, homeowners pay higher energy bills and have condensation on their window panes during colder winter months. Single glazing also has low acoustic insulation properties.

Retrofitting double glazing to wooden windows is done by removing existing single panes of glass and installing new slim-profile heritage double glazing.

We use slim profile, vacuum-sealed units with exceptional thermal insulation properties, equivalent to triple glazing. Our double-glazing installation methods ensure that important original characteristics of the historic property are preserved, living conditions are enhanced, and the extended service life is guaranteed.

Thermal imaging of our recent double-glazing projects

Thermal camera testing of our recent double glazing retrofitting projects.

heat loss analysis of double glazing
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Advantages of sash windows double glazing

Thermal efficiency

When compared to the thermal performance of single glass pane windows, double-glazed units reduce heat loss and improve the energy efficiency of original sash windows by up to x8.

Vacuum, slim-profile double glazing (only 6.7-10mm) with Low-E glass has the same thermal and insulation properties as 36 mm triple glazing. It also beats by energy performance the standard heritage double glazing with laminated glass and insulated with inner gasses such as Krypton and Argon.

improve thermal efficiency

Double glazing for sash windows: Single glazing, vacuum and triple glazing

Different glazing options for sash windows are compared by thermal efficiency, thickness and stability to fit existing original sashes.

To the box with different glazing options, we inflated hot air and used the thermal camera to capture the heat loss of each glass.

External noise reduction

By retrofitting double glazing to wooden windows, the noise pollution from outside your house will be reduced.

For example, the Fineo glass has an acoustic performance that reduces perceived noise by over one-third compared to single glazing.

If you live on a busy road, this reduction in external noise will help you sleep longer in the morning instead of waking up with the first commuters.

Better sound insulation
Noise reduction window


Double-glazed units are harder to break, so they increase the house’s safety.

Where required by building regulations, the units can be made using toughened glass (laminated glass or tempered), which is even more secure.

increased security

Increase the value of your house

The market value of your property will also increase after retrofitting. Whether you’re looking to sell your property now or might be planning it for the future, double-glazing can deliver great returns on your investment as windows are one of the most important parts of the house, one the poof comes before windows.

Our projects and customer testimonials

Testimonial — Trevor and Dee

Project: Double glazing Georgian sash windows with FINEO glass

Double glazing Georgian sash windows with FINEO glass

Watch Project

Testimonial – Sally

Project: Vacuum double glazing installation

Vacuum double glazing installation

Watch Project

How long does it take to retrofit double-glazing to wooden windows?

  •  After the quote is accepted, we take glass measurements and place the order with the glass manufacturer.
  • Manufacturing and delivery take an average of 6 weeks. The glass is either delivered to your address or our premises.
  • Once the glass is delivered, we do a quick inspection and schedule the work.
  • On the agreed day and time, our team comes and does all retrofitting, restoration and painting work.

On the 15-sash windows project, our team will usually spend around 12 working days. The work will include wooden frame refurbishment, retrofitting and painting.

Can you retrofit double glazing to any wooden window?

The most likely answer is yes!

There is a wide range of challenges involved in retrofitting double glazing to wooden windows. It all depends on the condition of the wooden frames, access to the window and the size required.

Specials shapes double glazing

Specials shape

Slim-profile double-glazing units are evaluable in special shapes: curvedfull-curvedtrapezoidal or oval shapes.

Specials shape double glazing units

Minimum and Maximum dimensions

Maximum: 1.50 m x 2.50 m or 1.60 m x 2.40 m
Minimum: 0.20 m x 0.20 m

Alternative to secondary glazing or new double-glazed sash windows

Vacuum-sealed double-glazing units are not visible when fitted into the sashes. The traditional sash windows with this new generation of double glazing look no different to how they looked with single glazing.

New double-glazed sash windows with standard double-glazed units and E-coating are 120-270% less efficient than the original sashes that our specialists retrofit with vacuum glass.

new double glazed sash windows compared to original window retrofitted with double glazing

The sash window secondary glazing, on the other hand, does change the appearance of the original windows. It is bulky from the inside, takes up much of the interior window sill space, and is noticeable outside.

The photos below show the window our team double glazed and a traditional sash window with secondary glazing:

Secondary Glazing vs double glazing

Common sash window double glazing challenges

We encounter and solve when installing double glazing, including weak frames which are not designed to take the extra weight. To solve this, we enhance existing frames with hidden metal frameworks and reinforced joints – cleverly installed to cope safely with the additional weight. In sash windows, all necessary counterbalance systems and mechanisms are adjusted and upgraded too.

Other restoration companies can find that the narrow rebates of original wooden windows make it impossible to install double-glazing without altering the authentic appearance. Because we use advanced, ultra-slim double-glazing units, we can comfortably work with original windows, without having to make drastic rebate alterations. At 6.7mm thick, the glazing we use is only 3mm thicker than an average single pane, yet is vacuum-sealed to provide the thermal properties of triple-glazing!

Can windows in listed buildings be double-glazed?

In most cases, yes! Technically and permission-wise, it is highly like that reglazing will be the best option for listed buildings.

Because of the progress in technology and manufacturing processes, we can create glazing units that were simply not possible back when your timber windows were originally designed and crafted.

The double-glazing units which we install are ultra-tough yet incredibly thin compared to average double- or triple-glazing. And because they are vacuum-sealed, they offer many advantages and improved performance.

What do revolutionary glazing products mean for your listed property? The thin profile allows us to professionally fit upgraded glazing without compromising on authenticity. The appearance and original design of your windows are not lost – typically, the rebate depth comfortably takes the new panes with only slight modifications needed.

Can windows in listed buildings be double-glazed

What are the different types of double-glazing glass?

We are able to provide a wide variety of glazing options to suit all different needs and window styles.

We expertly select and install the best double-glazing for sash windows to maximize benefits, comfort, and security. Here are some of the glazing options you could choose from:

  • Low E-energy Saving Glass
  • Toughened Safety Glass
  • Laminated Safety Glass
  • Vacuum insulated/insulated with gases
Low-E Coating Performance

Keep windows operational after reglazing

Additional glass panes also mean the addition of weight.

Thankfully, this does not impact the smooth operation, strength or safety of your windows. Correct adjustments of weight and pulley system will leave your sashes running even smoother, stronger and safer than before.

We replace and upgrade sash cords and re-balance your sash windows using additional weights.

When we remove sashes to fit in new glazing, we also check pulleys and replace them if required. We also straighten sash joints while doing other restoration work on wooden frames and sashes.

Repairing sash window frames during reglazing

To properly prepare wooden windows for safely accommodating the additional weight of your glazing upgrade, we provide all the services you need, including sash windows repair.

When we fit new vacuum glazing we repair box sash window frames and sashes because rot is a very common issue in historic windows.

Over time, original timbers succumb to the elements and need professional restorations to return them to full health.

We repair all rotten timbers and frames, as well as any structural damage, leaving them ready for secure new glazing installation.

Sash window before and after double glazing

Our team can reinforce weak frames and original joinery without impacting its aesthetic. We carefully assess each window to guarantee the best fit and provide a safe, smooth-functioning experience.

It is common practice for us to install draught-proof systems alongside fitting double-glazing. This further enhances the thermal, acoustic, and functional benefits.

Combining services such as double-glazing, woodwork repairs, decorations and draught-proofing as part of the same project is a great way to really optimise your living conditions, property value and all-around quality. These services all go hand-in-hand and provide an effective, efficient way to complete comprehensive restoration work.

repairing sash windows
woodwork repairs
repair of rotten wooden window frames
Retrofitting Double Glazing To Wooden Windows


How does double-glazing work?

The two panes of glass trap air in the small gap between them. This layer of trapped air insulates against heat transfer from the outside to the inside of a property and vice versus. The air between the panes is also a barrier to noise and condensation. So double glazing is basically a clear layer of insulation for your home.

How long does double glazing last?

Most double-glazed units use gas as insulation.

This gas is argon. Over time, this gas will dissipate and disappear. This typically happens in around five years. We use vacuum double-glazing technology at Chameleon, though.

Vacuum double glazing does the same job as gas-filled double glazing but lasts for much longer. Fineo vacuum double glazing comes with a 15-year guarantee and improved noise reduction, and a great deal more.

It is why we choose Fineo for all of our window restoration projects. It offers the same heat, noise and condensation protection as triple-glazed windows but in the form factor of double-glazing. It is highly energy-efficient and will insulate your home much longer than traditional double glazing.

What’s the difference between secondary glazing and double glazing?

Secondary glazing is an independent layer of glass that is added to the inside of your property, inside the existing window frame.

Double glazing is a sealed window unit with two panes of glass separated by an insulating space bar. The gap between the window panes can be filled with gas or vacuum sealed to create an insulation barrier.

Secondary glazing provides better acoustic insulation than gas-filled double glazing, but it is often unsightly and changes the character of a home.

However, double glazing is twice as effective at stopping heat from escaping from your home and is lower profile than secondary glazing, so it keeps the style the same.

A good quality vacuum double glazing, though, beats secondary glazing acoustic insulation properties and double glazing heat insulation.

That is why we use Fineo vacuum double glazing in all our window restoration projects.

How can I make my old windows more energy efficient?

If you have an older property with single-glazed windows, they can cost you a lot of money because of how inefficient they are at keeping the heat inside your home.

Double glazing is a great option for you. However, many restrictions exist for double-glazing units in older homes.

For example, listed buildings cannot have double glazing installed, which changes the character of the property. 

Chameleon installs ultra-thin double glazing into existing old sash window frames that keep the character of a property intact.

The conservation officer must give permission for FINEO double glazing, despite it being not much thicker than single glazing.

Why is double glazing better than single glazing at stopping heat?

Double-glazing is better than single glazing at stopping heat transfer because of the layers of glass.

Double glazing is a great way to keep your home’s temperature stable.

It acts as a barrier between the inside and outside, preventing cold or hot air from mixing with the air in your home.

Additionally, double glazed windows help block noise and condensation, keeping you comfortable all year round.

Will you need to take my windows away?

No, we complete all work on-site.

What guarantees do you offer?

We offer a 10 year guarantee on paintwork, 20 years on repairs and 15 years on Fineo glass.