Everything you need to design and specify timber sash windows properly, whether you are a homeowner replacing one window, or an architect or contractor specifying a whole terrace.
Anatomy of a sash window
A traditional box sash has two sliding sashes held in a box frame. The weight of each sash is balanced by cast iron or lead weights running on cords and pulleys inside the box. Getting the names right makes quotes and drawings easier to compare.
- Box frame: the outer frame, made of pulley stiles, head, sill and linings, with a hollow box either side for the weights.
- Sashes: the two glazed frames. The top rail, bottom rail and stiles hold the glass.
- Meeting rails: where the two sashes meet in the middle, usually fitted with a fastener.
- Glazing bars: the thin bars that divide the glass into panes, such as six over six.
- Horns: small extensions at the bottom of the upper sash stiles, typical from the mid-Victorian period onwards.
- Beads: the staff bead (inside) and parting bead (between the sashes) that hold everything in place.
Matching the period of the house
Glazing patterns and details changed over time, so a new or repaired window should match the building. Georgian windows tend to have slim glazing bars and many small panes, often six over six. Victorian windows moved to larger panes, two over two or one over one, often with horns. Edwardian windows often combine a divided upper sash with a single pane below. Our guides to Georgian and Victorian windows go into more detail.
What to include in a specification
- Scope: repair, refurbishment, new sashes in existing frames, or complete replacement.
- Timber: species and grade, for example Accoya, Sapele or engineered redwood, and whether it is finger-jointed or solid.
- Glazing: single, slim double glazing, vacuum glass or secondary glazing, plus any safety glass needed.
- Profiles: glazing bar, horn and moulding profiles, ideally matched to the existing windows or a sample.
- Balancing: traditional weights and cords, or spiral balances.
- Draught-proofing: brush or rubber seals to the beads and meeting rails.
- Ironmongery and locks: fasteners, sash lifts, restrictors and security locks.
- Finish: factory paint system, colour and expected repaint interval.
- Performance: target U-value and any acoustic or security requirements.
Glazing options
Slim double-glazed units and vacuum glass fit within traditional sash proportions, so they suit most period homes. Secondary glazing leaves the original window untouched, which is often the best answer for listed buildings. See our guides to double-glazed sash windows and secondary glazing.
Working with a sash window company
A good sash window company will survey each window, take profiles where needed, and give you drawings or a schedule before work starts. Ask to see the specification in writing so you can compare quotes like for like. Find a sash window company near you.