Box Sash Windows: Frequently Asked Questions

Box sash windows are the very definition of a statement window. Adding a touch of vintage glamour and townhouse decadence anywhere that they’re installed, they turn a functional object into a vivid decoration.

And more than just looking incredible, they can change the way a room feels as well. They allow sunlight to flood in, bringing swathes of space to the smallest of rooms. No wonder they’re such a perennially popular choice for period properties.

Installing or replacing sash windows can also feel like a significant change and almost a financial investment. It’s important to feel confident you’re making the right choice for your home.

If you’re considering installing box sash windows, but have concerns about the details of, here are our answers to some of the most common questions asked about sash windows.

What Are Box Sash Windows?

The traditional sash window is among the most iconic heritage window styles available. Eternally elegant and aspirational, it brings classical character to any property.

However the term ‘sash window’ actually covers two different technical designs. One is slide sash windows and the other is box sash windows.

Both styles of sash window open by sliding one pane over the other. This movement can be either up and down, or from side to side. Unlike casement windows, sash windows don’t have a hinge or open outwards. They just slot one behind the other to open.

How Do Sash Window Mechanisms Differ?

The terms ‘slide’ and ‘box’ refer to the mechanism that opens the window. This is controlled through a system of pulleys. These pulleys are weighted for resistance to keep the movement smooth, easy and effortless, even on heavy, awkward windows.

A slide sash window (also known as spiral balanced sash) is the most modern of the two designs. It uses a counterbalance which is created by a number of springs inside a PVC tube. It is the more secure style and is slightly easier to install. However this tube-based counterbalance system is visible on the window which can be a significant downside for something celebrated for it’s attractive, traditional appearance.

Also known as a “hung sash” or “cord and weight”, the movement when it opens defines what is a sash box window. Rather than using springs, it is weighted to create a counterbalance instead.

This is the more traditional style of sash window. In fact it is centuries old. It is a far cleaner, smarter design, and modern technology means it is still as secure and functional as it is attractive.

The name ‘Box sash’ comes from the box which covers this pulley mechanism. It not only hides the ugly workings of the window, it also protects them, giving them a far longer lifetime and the capacity to replace the pulleys without having to replace the whole window.

Can I Replace Box Sash Windows With UPVC?

It is definitely possible to replace an authentic box sash window with UPVC. Replacement uPVC windows essentially function the same as a wooden one and are more attractive than your average plastic double glazed window.

But just because you can, doesn’t mean you should choose uPVC sash  Georgian windows or other era-styles over wooden framed ones.

Choosing to install sash windows is a style statement for your home. Add a vintage period feel to any property. There is no denying the bright white sheen of uPVC will lessen the impressive impact they make. The authenticity of your traditional design is damaged, and a dull sense of disappointment may set in.

With a little of love and care, timber framed windows will work just as smoothly and last even longer than their UPVC counterparts.

Timber Sash Windows vs UPVC Sash Windows

Timber sash windows won’t be the cheapest option but they will look more authentic, and so much more attractive that the investment will never feel heavy. Their longevity also increases their value; wooden framed windows are simply more resilient than UPVC. This is why wooden windows tend to come with a longer guarantee to protect them and you.

In fact, choosing UPVC frames could end up costing you even more subtly in the long term. If you have a period property that is faithful in design to its heritage, choosing UPVC windows will undermine it’s authenticity and may even knock value off your home if you choose to sell it. If you are looking to replace an existing Victorian sash window it may not be possible to choose uPVC at all. Living in a conservation area, the distinctive appearance of historic buildings leads to tightened planning restrictions, meaning that using uPVC in your windows may well be out of the question completely. The tight planning laws are intended to preserve the heritage of the area, and there is no denying the glare of modern white uPVC will impact on that.

Useful link:

Find your Local Planning Authority for area specific information.

How Do You Measure For Replacement Box Sash Windows?

As sash windows are a traditional style, stretching back to the Georgian period, they aren’t always standard sizes. This makes it extra important to get exact measurements when you’re looking to buy replacements.

The added box for the opening mechanism can also make it a bit more complicated to measure for them.

This is why most companies will offer to take the measurements for you. They will send out experienced surveyors who will be able to take reliable,

However, if you need a rough idea of the size of your windows to help get price quotes, here are a few steps you can take.

How To Take Window Measurements For A Quote

Start with the height, measuring on the inside of the old frame (from jamb to jamb). If you want to be as precise as possible, do this three times – once at either edge and once in the centre of the frame.

Make a note of the smallest of these measurements. Next, you need to do the same with the width.

You should also measure for the squareness of the frame. You can do this by measuring across the diagonal of the window – top right corner to bottom left corner. Then flipping and doing top left corner to bottom right. If your existing frame is relatively square (out by less than a quarter of an inch) you can adjust a standard size window to fit the frame. If it’s more than that you may need to prepare to replace the frame as well as the window. A fully trained surveyor will be able to tell you for certain.

Windows & More provide bespoke windows to measure, so contact us with any measurements you have taken that don’t conform to standard sizes – we’ll build the solution for you.

How Do Box Sash Windows Work?

Box sash windows work on a series of pulleys and cords.

A sash cord runs from a pulley, across the top of the window, and is attached to a counterweight. These days, that weight is made of steel, though traditionally it was made of cast iron or lead.

When the window is opened, the cord pulls through the pulley making it easier to open, while the counterweight creates resistance and keeps the movement fluid and effortless.

What Period Are Box Sash Windows From?

Authentic box sash windows have actually been around since the 17th Century which explains their iconic appearance. They were cutting edge in design and technology and as desirable then as they are now. In fact the first architects known to sign off on the use of sash windows included Christopher Wren, the renowned architect who designed St Paul’s Cathedral.

Before this, sash windows had no ‘counterbalance’ system built-in. They were awkward and heavy to open, and looked far better than they functioned.

Having been around for hundreds of years, sash windows have followed fashion as faithfully as other interior design features.

Sash Bars

Many box sash windows feature a grid pattern. This is because they are made up of a lot of smaller panes of glass (or lights or mutins) that are held together using sash bars.

This is due to how long they have been in use. When sash windows were first created, glass could not be manufactured strong enough to make big, bright panes that were fashionable of the time. Instead, these smaller mutins allowed makers to build up the beautiful, broad windows we associate with period townhouses, without the weight of them shattering the glass.

These days, glass can be made strong enough to give much larger panes without risk. However, the grid effect of sash bars remains popular. And, if you’re looking to replace box sash windows in line with the period of your property the number of mutins is important to get right.

For example, Georgian windows would usually have a six over six grid. This is because glass was at its weakest then, but it also fed into the Georgian’s love of symmetry.

A Victorian sash window however is more likely to a simple two over two design, as they had advanced in glass making techniques, and preferred this simpler style.

Another period synonymous with sash windows is the Edwardian period. They went for a six over two design, bringing together the best of both the Victorian and Georgian options. Traditionally box sash windows were constructed using timber frames. This is why many people in the modern day chose to get timber, when it comes to the decision between wood or UPVC. It looks more authentic and traditional, in keeping with the wonderful heritage of these windows.

Looking To Replace Your Heritage Windows?

Our bespoke, handmade timber box sash windows are the perfect solution to replacing windows in period properties and in conservation areas.