Double Glazed Sash Windows

When you think of Sash Windows the image that springs to mind for most people is that of a creaky, ill-fitting window that let in draughts and cold, and are typically seen in Victorian houses. And this would generally be true for older none renovated properties.

However, the good news is that if you love the look of traditional Sash Windows, we have a solution for you! You no longer have to tolerate their foibles, as modern ones are a fabulous way to recreate this design element whilst still benefiting from a warmer, more comfortable, draught-proof home. We have a more modern alternative than older plain timber windows which can also be a great choice for conservation areas or a listed building.

They are the perfect combination of modern technology with a traditional style for your home, suitable for anyone! The double glazing brings beautiful, traditional Sash Windows up to date without losing their charm.

They are particularly useful for period/conservation properties as they are a great option for rejuvenation whilst being in keeping with the look of the building, even if it’s just for the rear of a property when the front must be timber. In order to help you determine whether Sliding Sash Windows are a good choice for your home, we present you with some of the most asked questions about them!

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What is double glazing and how does it work?

Double glazing is glazing that is made up of two panes of glass fitted into the same unit. The panes will have argon gas between them which helps to insulate the windows keeping warm air in and the cold air out.

Can all sash windows now be double glazed? Will I be allowed to install Double Glazed Sash Windows?

If you choose to have new Sash Windows installed they can of course be double glazed as it features two panes of glass, with an air gap in between. However, if you live in a house within a conservation area or a listed building then there may be some planning restrictions and you may need permission. 

Generally, you will need to prove that your existing sashes are beyond repair to obtain planning permission, therefore if you are unable to do this it may be an option to install secondary glazing instead and get new sashes.

Our Double Glazed Sash Windows Profile 

Double glazed sash window Profile

What materials are used to make double glazed sash windows?

Traditionally a sash window was made from timber; however, the modern alternative to wood is a UPVC sash window. Of course, both have their advantages and disadvantages. 

Double glazed timber sash windows can be manufactured from either softwood or hardwood. A sash window can also be found with softwood frames but with hardwood inserts, such as cills. Due to recent advances in technology, engineered woods are now becoming more frequently used in the making of wooden windows double glazed.

This engineered wood has a number of features that give it an advantage over “natural timber” when used for sliding sash windows. Engineered timber is very stable and made from laminated “cross-grain” sections of wood, which greatly reduces the effects of shrinkage, warping, and expansion which are three of the most commonly reported problems experienced with wooden sash windows.

UPVC double glazed sash windows can be made with much slimmer frames than those of a traditional wooden window which allows for a less bulky look. In addition, the UPVC sash window is known for its long life and low maintenance.

Installing a box sash would also be helpful. With the improvement in design and manufacturing processes, uPVC sash windows can offer wood-effect surface finishes that give the window a remarkably authentic appearance. Combine this with an extended choice of colour and you have an excellent alternative to timber sash windows that is well worth considering.

Are Double Glazed Sash Windows durable? 

The durability really depends on how well you maintain your windows. If a sash window is well maintained and looked after, it could easily last in excess of 25 years. Our Sash Windows are made of the highest quality materials that are designed to last and we are happy to advise on the correct maintenance procedures.

Will the double glazing alter the visual appearance of my Sash Windows?

In terms of visual appearance, there will be very little change with the new Sliding Sash Windows – this is unless you opt for a different look! The frames of your windows will be the same thickness as they were original although there will be small differences in the molding on the outside and the inside bead.

We will ensure that your new purchase is the perfect fit for your home, retaining the features and designs that make your windows double glazed beautiful.

Can double glazing be fitted into my existing sash window?

This would be extremely difficult to do as older Sash Windows weren’t designed to accommodate double glazing as the glazing bars are not generally deep enough to hold thicker panes in place. But if you look for a new sash window with secondary glazing we recommend replacing the existing sash in order to obtain a better performance and lasting durability.

Are Double Glazed Sash Windows energy efficient? 

Double glazing itself is known for being energy efficient and minimize heat loss a but the overall energy efficiency rating of your home will also be dependent upon a number of factors including wall and loft insulation, the installed heating systems, and the roofing material.

The windows, however, are a key factor in a house's overall energy cost-effectiveness rating, as they keep the cold and the wind outside as well as they are draught proofing, thus offering incredible performance.

 Installing windows sash could help you save on your energy and heating bills. Double glazed sash windows will also help the environment as you will have less need for heating systems when you have double glazing, so these new windows will reduce your energy consumption, due to their overall performance.

What are the key benefits of Double Glazed Sash Windows?

Reduces Energy Usage

These sash windows are well known for being highly energy-efficient because they seal very well due to their double-glazed. The sash window presses directly against all four sides of the frame of the window, forming an airtight seal that prevents air and cold spots from entering your house, providing incredible efficiency and guaranteeing draught-proofing.

Reduces Condensation

Double glazed windows limit air intrusion into your home and due to their incredible performance reduces condensation.

Reduces Noise

Since the glass of this type of window has two glazed units, noise reduction is just one of the many advantages of secondary glazing.

Increases Security

All of our sliding sash windows were proved to resist physical attack by a burglar by being sufficiently robust. Moreover, the glazed units are harder to break, thus improving the security.

Improves kerb appeal to enhance property value

Nowadays, more and more people are looking for inspiration in the past, and the sliding sash windows represent the perfect choice as it adds extra beauty and value to the house.

How much does a double glazed sash window cost?


In general, UPVC double glazed sash windows cost considerably less than double glazed timber sash windows. With prices starting from £500 upwards they are not the cheapest options compared to quick fixes like draught-proofing but are definitely cheaper compared to wooden sash window replacements, which can easily cost over £1,000. 

To give you an idea of cost, wooden sash windows can cost around £1,000 each, whilst UPVC double glazed sash windows price tends to be cheaper at about £350 per window. 

There are many factors that affect the cost of a double glazed sash window as follows:  

The Materials


The double glazed sash window is not the cheapest replacement window on the market, in particular, some timber sash windows can be quite expensive to replace. For many homeowners where there are no planning, covenants, or aesthetic reasons compelling the fitting of these windows, many choose to replace the original sash windows with casement windows.

However, sash windows are aesthetically pleasing, but of course, the price does depend upon the material. You can even opt for sash horns, but this will raise the price a little bit. For example, hand-built double glazed timber sash windows will be the most expensive.

This is largely due to the fact that so much extra work goes into crafting them and because they are so visually appealing, this extra cost is very often justified. Full softwood sash windows will usually be less expensive than any window using hardwood.

Engineered wooden sash windows, depending on the manufacturer, may sometimes be a little less expensive, but not always. UPVC is a relatively low-cost material to produce and can be fabricated easily into double glazed uPVC sash windows, so the relative cost is likely to be lower than for the same sized wooden windows. 

Type of Frame 

Generally, there are two types of double glazed sliding sash windows, these being box sash windows or slimline. UPVC replacement sash windows with double glazing would probably offer the slimmest profile frames and be the most cost-effective in relation to their performance.

A traditional box sash frame is a complex piece of work that requires an additional design tool and therefore commands a higher price. The addition of trickle vents for this type of sliding sash windows are also important as they combat condensation build-up in well-insulated homes, but this will of course add to the cost of your sash window.  

Timber windows are of course still standard nowadays as they offer good performance, and they come at affordable prices, with the glass being now double glazed. All traditional timber windows with secondary glazing can hardly be installed on the existing sash, so we recommend a new unit to be installed, which will come with a ten-year guarantee.

uPVC sash windows represent a more common choice than timber windows, even though they do not come with so many colour options. The reason for this is that uPVC sash windows are cheaper than timber windows.

The size of your double glazed sash windows and how many you will be ordering 

As with everything in life, it always follows that the larger the item the more it will cost! Therefore if you are ordering multiple replacement double glazed sash windows at the same time, it is very likely that you will find that the actual cost per new double glazed window will be reduced, the reduction being of course dependent upon the size of the order.

In the UK a standard window height is generally approx. 1200mm (4 feet) and the usual width of a standard individual sash window unit can also be in the region of 1200mm. Any window with a double glaze that differs from these generally accepted dimensions may be considered as “bespoke” by a manufacturer and therefore come with a premium cost as the sashes may need to have extra strength built in to meet the demands of the functionality. Larger window openings can be catered for by using multiple adjacent sash units (as discussed below).

The number of opening sashes

A typical double glazed sash window will comprise of two sashes. However, there is also the option to have one single hung double glazed unit or both sash windows with double glazed double-hung to open and close. If your new double glazed windows are particularly high then triple or quadruple hung double sections can be fitted but this is not a cheap option! 

Glass type and glazing options


In modern times, the fitting of single glazing in an external window is very rare. However, there may be instances, particularly within listed buildings, which come under a conservation order and/or planning restrictions, when single glazing has to be fitted.

This single glazing will be backed by internal secondary glazing (triple glazing) to ensure energy efficiency and reduce noise pollution, but will also significantly increase the price of the new sash windows.

The secondary glazing is standard for most replacement windows and by using low emissivity glass and gas-filled sealed units energy reduction will be improved even further - but of course, this will push up the price. More options are available and if required, leaded, patterned, frosted, or otherwise “special” glazing can also be fitted within the unit of design for these sliding sash windows at a premium price.

Surface finish and colour options

The white UPVC sash window is generally the most popular choice with homeowners, but coloured unit versions are available, including wood-effect finishes that will attract an additional cost. With double glazed timber sash windows, the box frame comes with more colour options., being easier to alter the colour by painting or staining, thus giving a touch of class to your home. In addition, the glass can be see-through or opaque, regarding the owner's preferences.

Interested in Double Glazed Sash Windows

Choosing new a new double glazed sash window can be a really hard task.

Why not ask us for a free no-obligation quote?

We can discuss your options in detail and keep in mind that all of our windows are available with a 10-year guarantee. Just pick up your telephone and call us!

Phone number: 0203 583 3525 or email for possible customers: