What Are Box Sash Windows?

Box sash windows are the classic vertical sliding window found in Georgian, Victorian and Edwardian properties across the UK. The name comes from the timber "box" built into the frame, which houses a set of weights and pulleys. These weights counterbalance the sashes, so a single window can glide open and shut with barely any effort, even on a large period property.

Unlike a casement window, which is hinged and swings outward, a box sash window slides straight up and down within its frame. Both the upper and lower sashes can usually be opened, giving you flexible control over airflow without a single window taking up extra room inside or out.

At Restore My Window, every box sash window is built from solid hardwood or Pine softwood in our workshop, using the same joinery methods that have kept period properties looking authentic for well over a century. No CNC shortcuts, no synthetic frames, just proper timber craftsmanship built to your exact measurements, backed by our full range of timber window and door services.

Why Homeowners Choose Timber Box Sash Windows

A look that suits period homes There's a reason conservation officers and homeowners alike keep coming back to sash windows. The slim timber sightlines and vertical proportions are part of what gives a Georgian or Victorian façade its character, and a well-made replacement will sit seamlessly alongside original features.

Effortless, quiet operation The weight-and-pulley system isn't just traditional for the sake of it. It does a genuinely good job, letting you raise and lower each sash smoothly with one hand, and keeping the window securely in place at whatever height you choose.

Ventilation without sacrificing space Because the sashes move vertically rather than swinging outward, you get the same airflow as a casement window without anything protruding into a path, patio or flower bed. This makes box sash a practical choice for terraced houses and townhouses with limited outdoor space.

Better thermal performance than most people expect Modern timber sash windows are a world away from the draughty originals. Ours are supplied with 135mm thick frames and argon-filled double glazing as standard, and we can also spec triple glazing where a higher level of insulation is needed. If you'd rather keep your existing frames, our double glaze and re-glaze service can upgrade them without a full replacement.

Noticeably quieter rooms The combination of a solid timber frame and double glazing does an excellent job of cutting down external noise, which makes a real difference if your property faces a busy road or sits close to a school or high street.

A genuine boost to property value Authentic timber sash windows are one of the few improvements that both estate agents and conservation-conscious buyers tend to agree on. They preserve the character that buyers pay a premium for, particularly in conservation areas where uPVC alternatives simply aren't permitted.

Built to last, with minimal upkeep With an occasional repaint and basic maintenance, such as keeping the sash cords in good working order, a well-made timber sash window will comfortably outlast most modern alternatives. Timber can also be repaired rather than replaced when damage does occur, which isn't the case with most synthetic frames.

Sensible security as standard Every window we build comes with modern locking hardware fitted discreetly into the frame, so you get proper security without the traditional look being compromised.

Speak to a Sash Window Specialist

If you're weighing up your options for a period property, our team can talk you through frame styles, glazing bar layouts and glazing specifications before you commit to anything. Get in touch for a free quote, or browse our full range of timber sash windows to see what's available to order online.

Frequently Asked Questions

What's the difference between a box sash window and a casement window? A box sash window slides vertically within a timber box frame, while a casement window is hinged at the side and opens outward like a door. Sash windows tend to suit period properties and don't need extra clearance outside to open, whereas casements can offer a slightly wider opening for ventilation.

Are box sash windows still made today? Yes, timber box sash windows are still handmade using traditional joinery, just with modern improvements like double or triple glazing, draught seals and concealed locking hardware built in.

Can box sash windows be double glazed? Absolutely. Most of our box sash windows come with argon-filled double glazing as standard, and we can offer triple glazing for homes that need extra insulation, such as properties near busy roads.

Are timber box sash windows draught-proof? A modern, properly installed box sash window with brush seals and correctly fitted weights will be significantly more draught-proof than an old, worn original. If you have existing sash windows that let in draughts, this is often down to worn cords, gaps around the frame or perished putty, all of which our draught proofing service can usually put right without a full replacement.

How long do box sash windows last? With basic maintenance, such as repainting every few years and keeping the pulleys and cords in good order, timber sash windows can easily last 20 years or more. Many original Victorian sashes are still in place today, over a century after they were fitted, particularly where they've had the benefit of proper wooden window restoration along the way.

What wood are box sash windows made from? We build our sash windows from solid hardwood or softwood, chosen for durability and how well it takes paint or stain over time. This is a key reason timber performs better long term than synthetic alternatives, which can't be repaired in the same way.

Do box sash windows need planning permission? If your property is listed or sits within a conservation area, you may need permission before replacing existing windows, and there can be restrictions on materials such as uPVC. Timber sash windows are usually the preferred, and sometimes the only permitted, option in these cases. It's always worth checking with your local planning authority or asking us for guidance, particularly if you're in one of the London conservation areas we cover.

What are the two types of sash windows? The two main types are single hung, where only the bottom sash opens, and double hung, where both the top and bottom sashes can be opened independently. Double hung is the more common choice, as it allows for better airflow control.

How much does a box sash window cost? Pricing depends on the size, glazing bar pattern, glazing specification and any bespoke requirements. The best way to get an accurate figure is to try our sash window cost calculator, send us your measurements, or request a free quote, and we'll talk you through the options.