Double-Hung vs Single-Hung Sash Windows: UK Comparison Guide

In a double-hung sash window, both the upper and lower sashes slide vertically, allowing either or both to be opened. In a single-hung window, only the bottom sash moves; the top sash is fixed in place. When closed, the two types look identical. The difference only becomes apparent when the window is in use.

Double-hung sash windows are overwhelmingly more common in UK homes. They have been the standard British sash window configuration since the 17th century. Single-hung windows are more associated with North American architecture. Most UK sash window manufacturers produce double-hung as their standard offering, with single-hung available as a cost-saving option.

Double-hung windows have one additional moving joint (the upper sash) compared to single-hung, which creates a slightly longer perimeter of potential air leakage. However, with modern draught-proofing systems using brush pile or compression seals, the difference is negligible. A properly draught-proofed double-hung sash window can achieve air leakage rates comparable to modern casement windows.

Technically yes, but it is rarely straightforward or cost-effective. The frame would need to be modified to accommodate counterweights or spiral balances for the upper sash, and the upper sash itself would need to be remade or modified to slide. In most cases, the cost of conversion approaches or exceeds the cost of full replacement with new double-hung windows.

Stack ventilation uses the natural tendency of warm air to rise. By opening the upper sash (allowing warm air to exit at the top) and the lower sash (allowing cool air to enter at the bottom), you create a continuous circulation of air without draughts. This is significantly more effective than ventilation through a single opening and is one of the key functional advantages of double-hung sash windows.

Most conservation officers expect like-for-like replacement, which for period UK properties means double-hung. If the original windows were double-hung — as virtually all traditional British sash windows were — replacing them with single-hung could be considered a material change to the building's character. Always check with your local planning authority before specifying single-hung windows in a conservation area.

Marginally. The fixed upper sash on a single-hung window cannot be forced open from outside, providing a small security advantage at the top of the window. However, intruders typically target the lower sash or meeting rail, where both types are equally vulnerable. Both types can be specified to PAS 24 security standards with appropriate locking hardware.

Each sash is connected to counterweights by cords (traditionally cotton sash cord, now often braided nylon) that run over pulleys at the top of the frame. The weights are concealed in boxes within the frame jambs. For a double-hung window, there are four weights — two for the upper sash and two for the lower sash. Each weight matches the weight of its corresponding sash, allowing the sashes to stay in any position without support.

Yes. Most uPVC sash window manufacturers offer double-hung as their standard configuration. The sashes are counterbalanced by spring or spiral balances rather than traditional weights, and many include a tilt-in feature that allows both sashes to be tilted inward for cleaning. Leading UK manufacturers of double-hung uPVC sash windows include Roseview, Masterframe, and Bygone.

The lifespan difference is minimal. Single-hung windows have one fewer moving sash, which means slightly less wear on the frame and fewer components to maintain. However, the difference in practical lifespan is perhaps 5-10% at most. Both types, whether in timber or uPVC, will last 25-60 years depending on material and maintenance. The mechanism (weights, springs, or spiral balances) is the most likely component to need attention over time.