As sash window experts, we are well placed to explain this unique type of window to our customers. People often want to know about the different components that make up a sash window, and to understand where it gets its name. We are regularly asked the question, “what exactly is a window sash”? So to help, we have put together this guide with details of sash windows, their anatomy and the way they work, to help you get your head around some of the terminology.

What is a window sash?

A window sash is a key component of a window frame that holds the glass panes in place. It is a rectangular or square framework that can be opened, closed, or tilted to allow ventilation and access to the outside. Windows typically consist of two main parts: the window frame and the window sash.

The sash is the movable part of the window that contains the glass panes. It can slide vertically (in the case of single-hung or double-hung windows), horizontally (in the case of sliding windows), or pivot from a vertical axis (in the case of casement windows). Sashes are usually equipped with mechanisms such as hinges, pulleys, springs, or tracks that enable them to move and stay in place when opened or closed.

Window sashes play a vital role in regulating airflow and providing natural light while maintaining a barrier against the elements. They can also contribute to the overall aesthetics of a building’s architecture.

How does a window sash work?

sash-window-with-astragal-bars (2)The sash is the name given to the frame that contains the glass, and there will usually be a top and a bottom sash in a typical window. If we are going to be specific, the full title of a sash window is a ‘vertical double-hung box-framed sliding sash window’! It’s quite a mouthful, so most people simply refer to them as ‘sash windows’.

The sashes will slide up or down with weights and cords, or more recently, spiral balances, allowing you to open the window. When closed, the top and bottom sash will be locked together at the midrail to prevent them sliding. There may be handles attached to the sashes to help you open them, depending on the window design.

The window can be opened by sliding the bottom sash upwards or, if you have a double hung window, by sliding the top sash downwards.

What sash windows look like

Understanding sash windows – the individual parts

There are various parts that make up a sash window and keep it working as it should. They give this type of window its distinctive appearance, as well as making sure it is thermally efficient and will open and close as needed.

These are the main components that make up a traditional, weights and cords sash window:

  • Sash, or sashes. There will usually be two sashes, which are the frames that contain the glass. They are moveable to allow you to open the window.
  • Box frame. This is the window frame that contains the sashes.
  • Sash cord. The cord is attached to the side of the sash and is fed through a pulley. It is also attached to the sash weight inside the box frame.
  • Sash weight. The purpose of the weight is to counterbalance the sash to allow the window to open. It will weigh the same as the sash, and will be made from steel, cast iron or lead.
  • Staff bead. A staff bead is an internal trim that sits around the box frame. Its purpose is to keep the sashes in position within their frame. Often, when you have a newer staff bead, it will also contain a draught seal.
  • Parting bead. This is a vertical seal that is fitted into the box frame and creates a channel for the top and bottom sashes. As with the staff bead, when you have a newer parting bead, it will often contain a draught seal.

Sash-DiagramSome window sashes will also have these additional features, which might alter the appearance or improve the functionality in some way:

  • Applied glazing bars. Astragal bars are placed across the panes of glass to make them look like smaller panes. In a modern window, they will be attached to one singular pane of glass on the inside and outside of the sash. A traditional Victorian or Georgian window would have been made up of multiple panes of glass, held within glazing bars. This was because glass used to be so expensive – if one pane broke, that was all that had to be replaced. It is now much cheaper to produce one single pane of glass, which is why the astragal bar is used instead, to give the appearance without the associated cost.
  • Sill. Most sash windows might make use of a sill on the inside or outside of the window. This is largely a decorative feature but may also help to protect the window from moisture and rot.
  • Draught-proof strips. These can be fitted to help improve the thermal efficiency of a sash window. Your window might already have them, as they are often included with a parting/staff bead (especially if the parting/staff bead, or the window as a whole, is quite new).

Glazing in window sashes

sash-window-with-astragal-bars (3)Modern window sashes will usually contain double glazing, and there are additional glass options you can choose from as well, like acoustic glass or safety glass.

There could be other factors that affect the type of glass you can have in a sash, including:

  • Listed building status. It can be challenging to fit double glazed windows in a listed building, as you will need to have the right permission to do so. It might be that you need to stick with single glazed windows and make sure they are as thermally efficient as possible by restoring the sashes. Alternatively, it may be possible to include Slimlite glass, which is very thin double glazing. The ideal glazing option for sashes in listed buildings or conservation areas is vacuum insulated glazing. This is a premium glazing option that can be easily retrofitted into existing sash frames due to its super slim profile however, it offers thermal capabilities greater than that of triple glazing.  We have also not had a planning application denied for this type of glazing to date.
  • The space within the sash. The glass will need to fit into the sash – if we are installing acoustic glass, for example, we will only do this if we are completely replacing the window. Old sash windows may need to be replaced if they cannot be double glazed.
  • Your budget. If you want to install a specialist type of glass, such as acoustic or safety glass, this will add to the cost of your windows. You can get a quote for different types of glass in your new sashes to see if it will be affordable.

How do you keep a window sash working as it should?

As with anything, a window sash will need to be maintained in order to keep it working as it should. If you have older sash windows in your property, they might require more maintenance to keep them in good condition. Newer sashes will need some degree of maintenance as well, even if it is just a new coat of paint every once in a while. The charm of a sash window is in its appearance, so most homeowners want to keep their windows looking their best.

If your sashes need more maintenance, it is perfectly possible to repair them and carry out an in-depth overhaul. Sometimes though, sashes are damaged beyond repair. In this instance, it is often possible to replace individual window sashes without having to replace the whole window. This can make the window much more thermally efficient, especially if you opt for double glazing in your new sashes.

Find out more about sash repairs

Repairing and replacing sash windows

If your property already boasts sash windows and they are showing signs of wear and tear, you may be pondering whether to repair or replace your sash windows? We have a wealth of experience in repairing and replacing sash windows, but if you are unsure what the difference between the services is, check out our blog for more information.

Is there anything else you want to know about window sashes?

Hopefully you now understand what a window sash is, and how it works within the sash window as a whole. If you have more specific questions about sash windows, please don’t hesitate to let us know. We are here to help.

Call Wandsworth Sash Windows on 020 3930 1379, email info@sashwindows.london or fill in our contact form.

    Contact the Wandsworth Sash Windows team

    Talk to us – we can help with your bespoke window, door and joinery requirements. Call 02079247303 or email info@sashwindows.london.