07Sep 2023

A Closer Look at the Anatomy of Sash Windows: Components & Functionality!

Posted in: Timber Types and Window Styles  –  By Patchett Joinery

The exquisite charm of sash windows, combined with their functional superiority, has made them a popular choice in the UK. These architectural gems are often a part of Georgian and Victorian houses, but their popularity transcends architectural styles and periods. This blog will explore the anatomy of sash windows to help you make informed choices when considering wooden windows.

Where Do Sash Windows Originate From?

Sash windows are a classic British invention, dating back to the 17th century. Their name ‘sash’ comes from the French word ‘chassis’, which means frame. Their simple yet elegant design and functionality quickly made them a standard in British architecture [1].

Vintage sash window with a white frame

Different Sash Window Styles

There are various styles of sash windows, including the single-hung sash where one of the two sashes is movable, and the double-hung sash where both sashes can be slid vertically. There’s also the horizontal sliding sash, where sashes slide horizontally.

Types Of Sash Windows

Sash windows can come in various forms, like the classic sliding sash window or casement window.

Parts That Make Up A Sash Window

The different components of a sash window

A sash window is made up of several individual parts, each of which contributes to the window’s structure and operation. Understanding the anatomy of these components can give you a better idea of how sash windows function.

1. Top Rail

The top rail forms the uppermost horizontal element of the sash. This sturdy element gives structure to the window, supporting the glass panes and helping to maintain the overall integrity of the window.

2. Box Frame

The box frame is a rectangular timber casing that houses the window sashes. This integral part of the window structure provides the necessary rigidity and stability, allowing the sashes to move smoothly.

3. Sash Cord

The sash cord is a robust cord that connects the sash weights to the sashes, ensuring they can move up and down smoothly. If these cords break, the operation of the window can be disrupted.

Sash Cord of a Sash Window

4. Weight Pocket

The weight pocket is the compartment located within the box frame that houses the counterweights. These weights ensure the sashes can be opened and held in position without slamming shut.

5. Parting Bead

The parting bead is a thin strip of wood that fits into the box frame. It keeps the two sashes apart, allowing them to slide past each other without friction.

6. Staff Bead

The staff bead, much like the parting bead, is a wooden strip that holds only the lower sash part in place. This bead also helps to create a seal when the window is closed, preventing draughts.

7. Meeting Bars/Rails

The meeting rails, found in the middle of the window sill, are where the top and bottom sashes meet when the window is closed. They create a seal that prevents drafts and helps secure the window.

8. Stile

The stiles are the vertical members of the sash. They form the sides of the window and provide a framework for the glass panes.

9. Apron

Located below the windowsill, the apron is a decorative piece that adds a touch of charm to the window’s exterior.

10. Box Sill

The box sill, or windowsill, is the bottom part of the window frame. This integral, trim piece protects the window from weather and enhances its aesthetic appeal.

11. Bottom Rail

Much like the top rail, the bottom rail forms the lower horizontal member of the sash. Its additional weight helps to balance the sash and enables smooth operation.

12. Weight

Housed in the weight pocket, the weight helps counterbalance the sashes. It’s attached to the sash cord, allowing the window to be opened and held open without additional support.

13. Wag Tail

The wag tail is a draught excluder that is attached to the sashes. It forms a seal when the window is closed, helping to keep your home warm and energy-efficient.

14. Timber Linings

Timber linings are strips of wood that are fitted inside the box frame. They help to reduce drafts and improve the window’s energy efficiency.

15. Pulley Wheel

Located in the box frame, the pulley wheel guides the sash cord, allowing the sashes to slide smoothly up and down.

Pulley Wheel of a Sash Window

16. Glazing Bar

The glazing bar, also known as a muntin, is a strip of wood or metal that separates and holds the individual glass panes in a glazed sash. It provides both structure and a traditional aesthetic to the window.

17. Soffit Lining

The soffit lining is fitted at the top of the window board and box frame. It prevents drafts from entering the weight pocket, helping to maintain the window’s thermal efficiency.

Sash Window Frame Types

The type of frame used in sash windows significantly influences their durability, energy efficiency, and overall aesthetics. Below are some of the most popular frame materials utilised in sash windows:

Traditional Timber Frames

Timber is the original material used in sash window frames, giving these windows their authentic, classic appeal. With timber frames, you’ll achieve an unmatched aesthetic that can significantly enhance the value and charm of traditional homes.

The benefits of timber frames extend beyond their visual appeal. Timber is a natural insulator, making these frames energy efficient. It’s also highly durable, especially when properly maintained. This type of frame can last for several decades, serving as a long-term investment for your home.

However, timber frames require regular maintenance to protect them from weather damage and ensure their longevity. They may need to be painted or stained every few years to maintain their appearance and functionality. Timber can also be more expensive than other materials, but many homeowners find that its aesthetic and longevity merits the investment.

Man making a traditional Timber Window Frame


uPVC, or unplasticised polyvinyl chloride, is a popular material for sash window frames due to its low maintenance and enhanced energy efficiency. These frames don’t require painting or sealing, which significantly reduces the upkeep they need.

uPVC frames are thermally efficient, helping to keep your home warm in winter and cool in summer. They’re also highly durable, resisting weathering, rot, and corrosion. Despite their durability, uPVC frames are lighter and more affordable than timber, making them a popular choice for many homeowners.

However, uPVC frames lack the classic charm and authenticity of timber. They’re also less environmentally friendly due to their plastic composition and the processes involved in their production.


Aluminium is another option for sash window frames. These frames are incredibly durable and resistant to corrosion, making them a long-lasting option for your windows. They’re also lightweight, which simplifies the installation process.

Aluminium frames are available in a wide range of finishes, allowing you to customise the look of your windows to suit your home’s aesthetic. However, aluminium is less thermally efficient than materials like timber and uPVC. To overcome this, many aluminium frames are designed with a thermal break, improving their energy efficiency.


Fibreglass is a relatively new material for sash window frames. It boasts high strength, durability, and low maintenance properties, much like uPVC and aluminium.

Fibreglass frames are highly insulating, making them an energy-efficient option for your home. They’re also highly resistant to weathering and degradation, ensuring they retain their appearance and functionality over time. However, fibreglass frames can be more expensive than other materials, and their aesthetic might not be as appealing to those seeking a traditional look.


Composite frames are made from a combination of materials, typically timber and aluminium or uPVC. These frames aim to offer the best of both worlds: the natural insulation and aesthetic of timber with the durability and low maintenance of aluminium or uPVC.

Composite frames are highly energy-efficient and require little maintenance. They offer a more authentic appearance than uPVC or aluminium alone, making them a popular choice for homeowners seeking the traditional look of timber without the associated maintenance.

Each frame material has its strengths and weaknesses. The best choice for you will depend on your budget, maintenance preferences, aesthetic goals, and energy efficiency needs. By understanding the characteristics of each material, you can make an informed decision that suits your home and lifestyle.

Functionality And Operation Of Sash Windows

Sash windows, also known as hung sash windows, are an iconic, decorative feature of British architecture. But what sets these windows apart is not just their timeless aesthetic appeal, but their unique functionality as well.

At its most basic, a sash window consists of two panels, or “sashes”, which slide vertically to open or close the window. This is possible due to a balancing mechanism that allows the weight of each sash to be effectively counterbalanced for smooth and effortless operation.

The vertical sliding operation is achieved using a counterweight system hidden within the box frame of the window. Each sash is connected by a sash cord to a weight. The weight is approximately equal to the weight of the sash box it’s connected to. As one sash is raised, its counterweight descends, and vice versa. This counterbalancing allows the sashes to hold their position when left partially open.

Some sash windows, known as “double-hung”, have both the upper and lower sashes operable. This provides excellent control over ventilation, allowing warm air to escape from the top opening and cooler air to enter through the bottom.

Modern sash windows have seen some advancements that enhance their functionality. For instance, some now feature a tilt function that allows the sashes to be tilted inwards. This makes cleaning the outside of the windows much easier, especially for windows located on upper floors. Others incorporate enhanced security features, improved energy efficiency, and noise reduction capabilities.

In summary, the functionality of sash windows combines the traditional charm of their design with the practicalities required by modern homeowners. Whether it’s their unique operating mechanism, ventilation control, or modern enhancements, sash windows offer a combination of form and function that’s hard to beat.

Average Cost Of Sash Windows

If you’re considering installing sash windows, understanding the cost implications is crucial for planning and budgeting. However, pinning down an exact price can be challenging as the cost can vary widely based on several factors. Here’s an overview of what influences the price of sash windows:


The size of your sash windows will significantly impact the cost. Larger windows require more material for the frame and glass, and often require more complex installation processes, leading to higher costs.


As discussed earlier, the material used for the window frame greatly affects the price. Traditional timber frames are typically more expensive due to their superior aesthetic and insulation properties. Conversely, uPVC frames are generally cheaper, while aluminium, fibreglass, and composite frames fall somewhere in between.


The complexity of the window design can also influence the price. Basic, single-hung sash windows are usually the most affordable option. In contrast, more complex designs, such as double-hung windows or those with intricate glazing bars, can increase the price.

Additional Features

Additional features like improved energy efficiency, enhanced security fittings, and noise reduction capabilities can add to the cost. However, these features can offer long-term savings and benefits that offset the initial investment.

Based on these factors, the price for a single sash window can range from around £500 for a basic uPVC model, up to £2,000 or more for a high-quality, bespoke timber window with additional features.

It’s also important to factor in the cost of installation, which can vary based on the complexity of the job and the rates charged by the installation company.

Remember, while the cost is an important consideration, it’s equally crucial to consider the quality, durability, and aesthetic appeal of your traditional sash windows. A high-quality, well-installed sash window can enhance the value of your home, provide energy savings, and offer long-lasting performance, making it a worthwhile investment.

Change In Sash Window Design Over Time

The sash window has stood the test of time, gracefully adorning buildings for centuries. However, like any enduring design, it has seen its fair share of change and evolution. Let’s take a look at how sash window designs have transformed over time.

Early Origins

Sash windows first emerged in the late 17th century, introduced by Dutch craftsmen. They were initially a luxury item, used predominantly in grand houses and palaces. These early designs were ‘single-hung’, meaning only the bottom sash could be moved while the top sash was fixed.

The Georgian Era

During the Georgian era (1714-1837), sash windows became more widespread. The typical Georgian sash window was six panes over six, with the upper and lower sashes each consisting of three panes across and two panes high. These windows were usually equal in height and width, providing a symmetrical look.

The Victorian Era

The Victorian era (1837-1901) ushered in a period of rapid technological advancement, impacting the design of sash windows. Larger panes of glass became more available and affordable, leading to the development of the ‘two over two’ design – two large panes of glass in both the upper and lower sashes. The Victorian era was also notable for the addition of decorative elements, such as ornate glazing bars and stained glass.

The Edwardian Era

During the Edwardian era (1901-1910), sash windows evolved further. The six-pane design made a comeback, but with a difference. In the upper sash, the central two panes were often larger than the surrounding four, giving the window a unique aesthetic.

Modern Innovations

Today’s sash windows retain their classic charm but have benefitted from modern innovations. Double glazing, improved seals, and energy-efficient glass have made sash windows more thermally efficient. Likewise, advancements in materials have resulted in the introduction of uPVC and aluminium sash windows, which offer durability and lower maintenance requirements while closely mimicking the look of traditional timber frames.

Additionally, modern sash windows often feature advanced mechanisms like spiral balances and tilt functionality for easy cleaning and better usability.

In conclusion, while sash windows have indeed changed over the centuries, their core appeal remains. Their ability to adapt to technological advancements while preserving their classic aesthetics is a testament to the enduring appeal of this iconic type of window and design.

Benefits Of Sash Windows

Sash windows are loved for their timeless elegance, superior ventilation, and the character they add to a home. Modern versions also offer excellent thermal and acoustic insulation, enhancing comfort and energy efficiency.

Grey sash windows in the workshop at Patchett Joinery

Trust Patchett Joinery For The Best Quality Sash Windows

If you’re considering installing sash windows in your home, trust the experts at Patchett Joinery. With over 175 years of experience, we specialise in crafting high-quality timber windows, including sliding sash windows that are perfect for both traditional and modern homes. Whether you’re in London or elsewhere in the UK, you can rely on us for your all sash window needs. Contact us today.


  1. “The History of Sash Windows in Britain”. Period Living. Retrieved from https://www.periodliving.co.uk/advice/the-history-of-sash-windows/
  2. https://historicengland.org.uk/images-books/publications/traditional-windows-care-repair-upgrading/heag039-traditional-windows-revfeb17/