Spring Sash Windows vs Box Sash Windows

• 24 June 2025|
• News

Windows aren’t just about letting light in. For homeowners as well as professionals like architects, developers and housebuilders, the right timber windows are fundamental to a project’s aesthetics, performance, and long-term appeal.

But before you settle on a style, it’s important to understand the two main contenders: spring sash windows and traditional box sash windows. Deciding between them requires a clear grasp of their unique characteristics.

At Lomax + Wood, we specialise in beautiful, high-performance timber windows and doors, all designed and crafted to meet your precise needs.

In this article, we’ll explore the nuances of spring sash windows and box sash windows, arming you with the knowledge to pick the perfect style for your upcoming project, be it a brand-new development or a historic restoration.

What is a sash window?

A sliding sash window is a type of window made with one or more movable panels, or “sashes,” that slide vertically to open. Historically, these windows were a hallmark of Georgian and Victorian architecture, known for their elegant proportions and excellent ventilation.

While their traditional appearance remains highly sought after, modern timber sash windows from Lomax + Wood incorporate advanced glazing and manufacturing techniques to offer superior thermal efficiency, acoustic performance, and security.

At a glance: spring sash windows vs box sash windows

Both spring sash and box sash windows have their own benefits and advantages.

Spring sash windows

• Utilises a spiral balance mechanism, concealed within the window frame
• Sleeker look, often preferred in modern builds or where a flush reveal is desired
• Generally a more economical solution, often used in new builds where competitive costs are key
• Highly versatile for new builds and renovations where a sleek, contemporary look is desired, yet historical accuracy is still important
• Generally simpler maintenance due to fewer moving parts and no exposed cords

Box sash windows

• Operates with traditional weights and pulleys, housed within a “box” section on either side of the window frame.
• More robust frame appearance due to the integral weight boxes, ideal for period properties.
• Installation can be more involved due to the need to accommodate the weight boxes
• An ideal choice for historic properties, conservation areas, and where authentic period detailing is paramount
• May require occasional re-cording of the weights and pulleys over a very long lifespan

Spring sash windows from Lomax + Wood

Our spring sash windows offer a blend of traditional aesthetics and modern performance, making them an excellent choice for a wide array of projects, including more modern builds.

One of the primary advantages of spring sash windows is their cost-effectiveness compared to more historically accurate box sash styles. This makes them particularly appealing to developers and housebuilders where build costs need to be more competitive.

At Lomax + Wood, our spring-balanced sash windows come factory double-glazed as standard with additional glazing options to ensure optimal insulation. They are fully weather-stripped for superior thermal and acoustic performance, ensuring your properties are energy-efficient and quiet. We can offer U-values as low as 1.1W/m²K., and sound reduction up to 42dB.

All of our timber products are made to order, allowing us to meet specific architectural requirements while incorporating practical features such as secure locking systems, durable finishes, and appropriate glazing options.

Box sash windows from Lomax + Wood

For projects demanding the utmost in authenticity and historical accuracy, our timber box sash windows are the perfect choice. These windows feature the classic weight and pulley system, housed within a ‘box’ section integrated into the frame.

Our timber box sash windows are crafted for both elegance and longevity, boasting timeless aesthetics alongside modern thermal efficiency. They are especially ideal for heritage homes and properties located in conservation areas. The design of the box sash window, with its substantial frame, lends itself perfectly to historical renovation projects.

Our timber box sash windows offer impressive thermal performance, with a standard U-value of 1.3 W/m²K and an optional upgrade to 1.1 W/m²K. As with our spring sash windows, we can offer noise reduction of up to 42dB for superior sound insulation.

Customisation options for sash windows

As with all of our timber windows and doors, our products are made to order. This allows you to specify everything from timber species and glazing options to colours and hardware. Both our spring and box sash windows are available with an endless range of customisable design options, allowing you to find the perfect fit for your project.

Which style is better for a conservation area?

When working on listed buildings or within conservation areas, in nearly all cases the local planning authority will require the replacement windows to match the original window design. Given their traditional construction, box sash windows are almost usually the preferred choice for such projects.

Our timber box sash windows can be specifically designed to meet the rigorous requirements of conservation areas and listed buildings, ensuring a perfect blend of heritage and modern performance.

Sustainable box and spring sash windows from Lomax + Wood

At Lomax + Wood, environmental responsibility is central to our manufacturing philosophy. We source all timber used in our bespoke windows and doors with full Chain of Custody certification (FSC® or PEFC), ensuring complete traceability throughout the entire supply chain, from the forest to the finished product.

Find the perfect sash windows for your project

At Lomax + Wood, we understand that every project is unique, and the choice of sash window depends on a multitude of factors, from architectural style and budget to performance requirements and planning regulations.

Whether you require spring sash windows for a contemporary development or authentic box sash windows for a heritage restoration, our team of experts is here to guide you.

Get in touch for your free quote or to discuss your home improvement plans. You can use our online contact form, or call us on 01277 353857 or book an appointment to visit one of our showrooms.