Sash Window

A sash window is a window made of one or two moveable panels (called sashes) that slide vertically within the window frame to open and close. The most common type is the double-hung sash window, where both the top and bottom sashes slide, allowing you to open the window from the top, bottom, or both for ventilation. A single-hung sash window has only the bottom sash moveable, with the top fixed in place.

Sash windows and renovation

Sash windows are iconic features of Georgian, Victorian, and Edwardian properties in the UK, and are found in many older American homes, particularly colonial and Federal-style buildings. During a renovation of a period property, decisions about the windows are among the most important — and most debated.

Repair vs. replace

If your property has original sash windows, you have three main options:

• Repair and refurbish — strip the existing sashes, repair any rotten timber, replace broken cords and pulleys, install draught-proofing strips, and repaint. Preserves the original character and is usually the preferred approach in conservation areas or listed buildings.
• Slim-profile double glazing — replace the single-pane glass with slimline double-glazed units that fit into the existing timber frames. Improves thermal and acoustic performance while retaining the original frames.
• Full replacement — install new sash windows that replicate the original style. Available in timber, uPVC (less authentic but lower maintenance), or aluminium. New windows offer the best thermal performance but are the most expensive option.

Draught-proofing

Original sash windows are notoriously draughty. Professional draught-proofing involves fitting discreet brush or rubber seals into the frame and between the sashes. This can dramatically improve comfort and reduce heating bills, and is far cheaper than full replacement. It is often the best first step for period properties.

Planning and conservation

In the UK, if your property is in a conservation area or is a listed building, you may need planning permission or listed building consent to change windows — even to replace like-for-like. Local planning authorities often require any replacement windows to match the original style, material, and glazing bar pattern. In the US, similar rules may apply in historic districts. Check with your local authority before including window replacement in your renovation plans.

Cost factors

Sash window costs vary widely depending on whether you are repairing, refurbishing, or replacing, and whether the windows are timber, uPVC, or aluminium. Bespoke timber sash windows made to match original period details sit at the premium end. When reviewing quotations, check whether the price includes removal and disposal of old windows, making good the surrounding plaster and architraves, decoration, and any scaffolding required for upper-floor windows.