For a vertically sliding sash window to remain open, a counterbalance system is necessary to offset the weight of the glazed frame. In this article, we explore the various types of balance systems that have been developed over time.

The vast majority of traditional wood sash windows are double-hung box frames, where both the upper and lower sashes operate independently. Each sash is suspended by cords attached to concealed weights, allowing smooth vertical movement. In our view, this simple system, first introduced in the 17th century, remains unmatched in effectiveness - later systems have largely been cheaper and less reliable alternatives.

Single-hung box frames, by contrast, are far less common. In these designs, typically only the lower sash is operable. Single-hung windows were often used in remote communities where transporting heavy sash weights by horse and cart posed logistical challenges. In some cases, local materials were used to fabricate weights, or the counterbalance system was eliminated altogether, replaced by basic sash pins or swivels.

During periods of rapid construction, such as the building booms following World War I, more affordable mass-produced solutions became necessary. Iron-framed casement windows gained popularity after the First World War, while spring balance systems became widespread after the Second.

Manual Holding Systems

Swivel Block

One of the earliest methods for holding a sliding sash window open was the swivel block—a simple physical stop that pivots into position beneath the sash to prevent it from dropping.

Sash Pins and Spring Bolts

Sash pins, or spring-loaded bolts, lock into holes drilled along the window jamb at regular intervals, typically every six inches. This was the least expensive solution for sash windows and became commonly associated with the term "guillotine windows" due to the sudden and often forceful closing motion if the pins failed.

Historic sash pin and window spring bolt examples from a vintage window hardware catalog — Historic sash pins, window spring bolts, and cast iron sockets featured in a vintage hardware catalog, showcasing traditional hardware used in restoring or preserving old sash windows.

Sash Window Balance Systems

Traditional Weighted Box Sash – Pulley and Cord

In a traditional box sash window, iron (and occasionally lead) weights are attached to cords that pass over pulleys and are secured to the sash frame. As the window is opened or closed, the concealed weights rise and fall within channels inside the frame.

Close-up view of exposed sash weight pocket showing pulleys, sash cord, and cast iron counterweight — A view inside a traditional wooden sash window frame, revealing the sash weight pocket with pulleys, cotton sash cord, and a cast iron counterweight for smooth window operation.

When changes are made to the window—such as installing heavier glass—the counterbalance must be adjusted by adding small lead castings known as "make-weights."

Two cast iron sash window weights placed on a bathroom scale for weighing — Cast iron counterweights from a traditional sash window, displayed on a bathroom scale to measure their weight before reinstallation or replacement.

This system remains the gold standard for sash windows when properly set up:

The momentum of the weights provides a smooth, gliding movement.
It is a proven, simple, and durable design.

Early sash cords were made from hemp or jute, but later, pre-stretched braided cotton became the standard. Selecting the correct cord diameter is crucial: if the cord is too thick, it can jam the pulley; too thin, and it may slip between the wheel and its housing.

Occasionally, sash chains were used for their durability, but they generate noticeably more noise during operation, even when used with specially designed wheels. Where original sash chains are present, they should generally be preserved for authenticity, although modern sash cords offer excellent longevity and performance.

Vintage illustration showing different sizes of traditional sash cords with labeled diameters

Vintage catalog page showing types of sash chains and chain fixtures for double-hung windows

Sash Window Spring Balance

By around 1880, metal springs began being used to counterbalance sash windows. Early designs featured springs approximately twice the height of the sash, allowing the window to spring open once the fastener was released.

Vintage diagram of an Anderson sash balance spring mechanism for window sash support — A historic diagram of an Anderson sash balance, a spring-based alternative to traditional sash weights and pulleys, designed to support double-hung window sashes.

The development of metal spring technology continued throughout the 20th century, and today spring balances are the most commonly used system in mass-produced windows—whether made of metal, plastic, or timber.

Sash Window Spiral Balance

Invented in America in the 1930s, spiral balances gained widespread popularity after World War II. These spring-based systems offered a more affordable method of manufacturing vertical sliding sash windows, although not necessarily a better-performing one.

Close-up view of a modern spiral balance for supporting window sashes — A modern spiral balance system designed to counterbalance window sashes without the need for traditional cords, pulleys, or weights, commonly used in contemporary sash window restoration and manufacturing.

All spiral balance variations rely on a spring to counter the weight of the sash, preventing it from dropping. Unlike traditional weighted sash systems, they do not offer a smooth gliding motion. Early spiral balances were encased in metal sheaths, but modern replacements often use plastic housings.

Key features:

Available in a wide range of sizes to suit virtually any window.
A proven, economical solution with decades of reliable service.

Sash Tape Balance (ACME Balance, Pullman Coils)

The sash tape balance system can be traced back to the late Victorian period, though it did not gain widespread popularity until the post-World War II building boom.

Vintage catalog page listing Caldwell sash balances with specifications for side and overhead patterns — A historic catalog page featuring Caldwell sash balances, offering specifications for side and overhead mounting styles, weight ranges, dimensions, and pricing for traditional window sash support systems.

Operating similarly to a retractable tape measure, this system connects a fabric or metal tape to the bottom of the sash. As the window opens, the tape retracts into a housing that contains a pre-tensioned spring, providing the necessary counterbalance.

Vintage catalog page showing Pullman all-steel sash balances with side and top mount options — Historic catalog page featuring Pullman all-steel sash balances for supporting window sashes up to 100 pounds, with specifications for side and top mounting patterns.

Larger windows typically require two balances per sash—four per double-hung window—whereas smaller sashes often use a single balance, sometimes paired with a sash roller or a simple metal strip on the opposite stile.

Sash tape balances saw extensive use in the United States and Australia while not having as much popularity in the UK.

Other Balance Systems

Sash Window Jamb Liners (Tilt & Slide)

An evolution of the spring balance system, jamb liners allow sashes to tilt inward for easier cleaning. In practice, few homeowners regularly use this feature, and these systems are often prone to failure, as much of the weight rests on fragile plastic lugs that wear out over time.