How do sash windows work?

box sash windows

Traditionally, all sliding wood sash windows were operated by cast-iron weights. Nowadays there is a modern spring mechanism option. We look at both types for wooden sash windows.

Wood Sash Windows on Weights

A sash box of 98mm is built into each side of the window, which houses the weights. This is attached to a piece of sash cord, which travels over a pulley in the top corners of the window and attaches to the sash that’s sliding. The sash windows using weights is selected to closely match the weight of the sliding sash so that a perfect counter-balance is achieved and movement of the otherwise heavy window sash is as effortless as possible.

Spring Balances

The use of weights and pulleys in modern sliding sash windows has declined over recent years and has largely been replaced by the spring balance system. Sash windows on springs work using similar principles of counterbalancing but achieve it through the use of two springs inside a PVC tube. Spring balances are usually visible on the inside of the window. However, a cover paint matched to the window will offer total concealment when manufactured. This makes the windows with spring balances almost perfectly reflect the style of those with weights and pulleys.

To help in opening windows, as well as hold windows open and closed, spiral balances utilize a spiral-shaped rod within a tube. This rod connects to a spring, which provides the tension for supporting the sash. The tension is adjusted by being wound the sash it is supporting.

Should I choose weights or springs?

Both systems have pros and cons, and the right system for you will depend on your location, the reveals in the window opening, and the desired impact you are trying to achieve. Weight and pulley systems have a nostalgic and historical feel, they’ll fit neatly behind traditional reveals, these systems also last longer (many decades) and repair means simply fitting a new sash cord. Spiral balances systems fit neatly into all building/reveal profiles without reducing light.

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