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Sash Windows: Types, Costs, Pros and Cons

a bay window on the exterior of a house with sash windows
(Image credit: Chris Snook)

Not only are sash windows a desirable original feature in a period property, they're also popular for new builds looking to create heritage-inspired elements in the design of a new home.

Your experience of sash windows might well depend on which of these types of property you come across. Original sash windows, you might find, are single glazed, draughty and often have a timber frame in need of repair. New sash windows, on the other hand, are double-glazed (at least), thermally efficient and may even be made of alternative, more durable materials than timber.

Whatever your sash window experience, and whether you're looking to install new ones or maintain and repair old ones, it's a window style that's full of character and charm, adding to your home's kerb appeal and potentially even it's value.

In our complete guide, we look at everything you need to know about sash windows.

What is a Sash Window?

The word ‘sash’ refers to a single frame for glazing. The sash sits inside the frame, which is fixed to the house. In a casement window the sash opens via a crank handle, while a traditional double-hung sash window features two sashes, split into a number of panes, that slide up and down, or very occasionally side to side. 

These horizontally sliding sash windows are also known as Yorkshire sash windows or ‘slider’ windows. This design actually pre-dates the vertical sash and although they use the same sliding mechanism, one of the sashes is usually fixed in place.

Sash windows are most commonly found in Georgian and Victorian properties, but can also be seen (with some variations) in late Victorian and Edwardian houses.

"This window style is still widely used on traditional-style new and self builds," says self build expert Mark Brinkley. "Sizes are typically non standard but windows need to be in proport­ion to the house, so are often bespoke."

a bathroom with a new sash window

All in One Design & Build (opens in new tab) replaced the existing window in the bathroom of this period farmhouse property with a modern sash window, which can be inverted to make cleaning the exterior of the window easier.  (Image credit: All in One Design & Build)

How Do Sash Windows Work?

Top tip

Insulation can be retrofitted into the counterweight pockets in older windows. 

Most traditional sash windows work with a system that balances the sash with a steel, cast-iron or even lead counterweight. This weight is hung on a cord that's located in a box within the frame. 

In modern sash windows, you're more likely to find a spring balance (or sash balance) system. This is a spring-loaded device which counters the force of gravity, in effect holding your sash window open without the need for cords, pulleys and those metal counterweights. 

Pros and Cons of Sash Windows


  • Offer a classic, heritage good looks.
  • Because sliding sash windows open at the top and bottom, they create great convection, cooling and ventilating a room more efficiently in hot weather. 
  • Windows can generally be locked ajar, meaning you can have an open window without as many security concerns. 


  • They're expensive
  • They're more complicated systems and harder to maintain
  • Painting windows is more complex with sash windows
  • Cannot open fully like double casement windows as there's always the size of one sash over the window. 

Are Sash Windows Worth It? 

In a new build, sash windows offer a prestige and quality that's hard to match, especially for a period-inspired property. Though the cost will be higher than a standard window, either PVCu or timber, modern sash windows will last far longer with the right maintenance, making them a good investment for your home. 

Any property from the 17th to 19th centuries would be lacking without sash windows; if you’re renovating a Georgian, Regency or Victorian property, or building a new home inspired by these periods, installing or renovating sash windows should be your top choice when it comes to windows styles. In a Conservation Area, or when renovating a listed building, you may not have a choice but to opt for sash windows. 

Identifying Different Styles of Sash Window

When fitting replacement sash windows in an older property, or choosing new sash windows for a period-style self build, it is crucial to get the time period right. There were several developments and style changes over the years. 

Sash windows traditionally consist of a number of small panes, or ‘lights’. These are held together by glazing bars – astragal bars – to create a larger glazed area. This is because glass technology at the time didn’t allow for very large expanses of clear glazing. 

The period of the house will dictate the number of panes in each sash separated by astragal bars:

  • Georgian: The ‘six over six’ style is the quintessential choice for building a Georgian style house, although larger ‘eight over eight’ windows were also common

wooden sash windows

This Hamptons-inspired Georgian self build features six-over-six sash windows to complete the period look. (Image credit: James Ram of Chetwode Charles)
  • Victorian: ‘Two over two’ reigned supreme in Victorian times, but many other configurations can be also found through the whole period. This included sash windows with just a single light, as well as the inclusion of sidelights 

victorian sash windows in a home with a contemporary extension

As is typical of Victorian buildings, this extended terrace has ‘two-over-two’ sash windows. (Image credit: Create Bespoke)
  • Edwardian: Typically ‘six over two’ panes was most common, but, as with the Victorian era, the Edwardians saw variations in style

Other variations in sash style include: 

  • Venetian windows which consist of a central sliding sash between two fixed panes either side
  • The Queen Anne Revival styles incorporates several panes in the upper sash but just one or two in the lower
  • Sashes were often arched instead of rectangular in Regency or Gothic revival periods, and in some regions it is popular to have horizontally-sliding sashes

Do Sash Windows Need a Lot of Maintenance?

Any style of timber window needs regular maintenance to hold on to their good looks and to work well over the years. That said, modern stains and other products can help reduce the frequency of this. 

More complex jobs will benefit from the services of a professional, but there are some jobs that can be done on a DIY basis.

Minor cracking or flaking in paintwork is a common issue which should be looked at every five or so years for external paintwork. As the paint protects the timber beneath, keeping a firm eye on any deterioration will ensure the frames won’t rot or swell.

Can Sash Windows be Double Glazed? 

Whilst it is possible to fit single glazed units on many sympathetic restorations, modern building regulations make it near impossible to have single glazed windows on a new house and there are many new timber products with double glazed sash designs.

Growing concerns about the energy efficiency of period properties might also steer you in the direction of replacing single panes with double when renovating. While it is possible, it needs close attention to be sure the delicate look of a sash window is not lost in modernisation. 

Dividing up small units of double glazing with thick bars tends to look clumsy, but there are ways to effectively recreate fine glazing bars. The best way is to bond mock bars onto either side of a single double glazed unit. You could also incorporate spacer bars between the glass sheets, at a higher cost, to add to the effect.

a period style property with sash windows

While working on an older renovation project, it is usually worthwhile taking a look into improving energy-efficiency where possible, including investigating replacing single panes with double glazing. (Image credit: Ventrolla)

Triple glazed window options are available in these traditional styles, but as with all triple glazed windows, it might come at a premium. However, modern triple glazing could be seen as no longer carrying the cost stigma that was attached for the last couple of decades. This is in the majority due to triple glazed windows being manufactured in mainland Europe where it is much more mainstream.

Replacing Sash Windows

Can Sash Windows be Replaced?

triple glazed sash windows

If the window frames are beyond repair, Green Building Store (opens in new tab) offer triple-glazed energy-efficient replacements. (Image credit: Green Building Store)
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While sash windows can be replaced, whether you’re updating your existing home or taking on a period renovation project, be careful not to make the mistake of removing period timber sashes that could be saved. 

Where they can be restored, re-conditioned and waterproofed, it is always worth holding onto the original windows or box sash, as new window sashes can be made to fit the existing frame, lowering the price of the replacement. 

However, if the windows are beyond repair or if there aren’t any left in place, many companies manufacture authentic replacements.

newly installed sash windows in a modern renovation

This cottage in Powys had ill-fitting PVCu windows which detracted from its original character so the owners chose to fit replacement sash windows. The newly installed sash windows have been colour matched to tie both the roof to the old cottage and the new glass link extension. (Image credit: Simon Maxwell)

What Material is Best for a Replacement Sash Window?

For traditionalists or for those living in a Conservation Area or listed building, genuine timber sash windows are likely to be the first (and only) choice. Sadly, plastic cannot achieve the same tactile effect and it can be hard to achieve the finer, more delicate details.

  • Durable
  • An excellent insulator
  • Long lasting (if properly maintained)
  • Modern finishes are available in most paint colours and stains. Modern developments also mean that timber windows are no longer high maintenance

PVCu (sometimes seen as uPVC) is often used as a substitute for painted wood. Though most commonly seen in white, it comes in a wide range of colours and finishes, including a photo-effect wood finish. However, if you live in a conservation area or in a listed building, changing to plastic sash windows will most likely be frowned upon. 

The benefits of PVCu include:

  • Low maintenance
  • Energy efficient (but not sustainable as they cannot be recycled)
  • Cheaper than timber (PVCu can cost around 40% less)
  • Better quality models are more attractive and hard-wearing but difficult to repair

It is becoming popular for sash windows to be composite in their construction. Newer products offer timber on the interior with aluminium cladding on the exterior.

Benefits include:

  • They retain the classic look of wood on the inside
  • Outside are extremely low-maintenance
  • Able to withstand all weathers

How Much Do Replacement Sash Windows Cost?

Installing new sash windows into an existing house or in a traditional-style self-build will generally be a more expensive job that than having casements fitted, but the extra cost for added character or a realistic recreation is usually worth it. 

As with most windows, uPVC sash windows are cheapest, but lack the finish of traditional timber.

Here's the average cost for a replacement sash window:

  • PVCu: From £950 for a larger sash window. Timber effect finishes will cost more. 
  • Timber and composite: From £1,300

Repairing Sash Windows

Should I Repair or Replace my Sash Window?

Most issues with timber windows can be fixed, including foggy windows, rotten frames and sticking sashes and a professional will be able to assist in making the decision in whether to salvage or replace but ultimately, the decision to keep original sash windows is down to customer preference and budget.

The benefits of repairing sash windows where possible include: 

  • House retains original charm and character
  • Homeowners benefit from improved thermal performance with double glazing and draught proofing if the box frame is retained and glazing is replaced
  • Original timber is generally of better quality than the products we can purchase today
  • Properly repaired timber windows can last another 100 years with a bit of care and attention

How Much Does it Cost to Repair a Sash Window?

Glazing can be replaced in sash windows and if the original frames are in good condition, single-glazed panels can be upgraded to slim double-glazed units. Also new sashes can be fitted into existing frames for which sash window repair specialists Ventrolla (opens in new tab) estimate around from £1,000 per window. 

For the complete replacement of sash window, cost will depend on specification (glazing types, choice of timber and any special feature of detailing required). You can expect to pay approx. from £1,750 per window.

contemporary sash windows

By repairing their sash windows and refurbishing them to suit a contemporary style, the homeowners of this period home have retained its character and charm (Image credit: Ventrolla)

How to Clean Sash Windows

If you're used to being able to lean out of a window to give a window a quick clean in between window cleaner visits, you may have to adapt in a home with sash windows. When you lift a sash window, it covers the other sash, so without access from the exterior while the window is closed, you won't be able to reach one of the sashes.

However, modern sash windows may incorporate sashes that also invert, into the room, helping to make cleaning these windows from the inside easier.

Melanie is a journalist who worked on Homebuilding & Renovating before becoming Editor of its sister title Period Living.