How Sash Windows Work

1. Top Rail: The top horizontal framing member of a sash. Rabbeted (SEE GLAZING BAR) on the outside.

2. Box Frame: Sometimes referred to as a ‘jamb’, the main box frame consists of three TIMBER LININGS.

3. Sash Cord: Runs over the PULLEY WHEEL and holds the WEIGHTS. It can be bought in rolls when it needs replacing (the waxed type is best). Chains are an alternative.

4. Weight Pocket: The WEIGHTS hang in the pockets created by the TIMBER LININGS on each side of the window. Insulation can be retrofitted in the pockets of older windows.

5. Parting Bead: A long, narrow vertical seal that fits in the BOX FRAME to form separate channels for the upper and lower sashes to run in, and holds the top sash in place. Newer beads often have built-in draught seals. On the upper sash, the bead is fitted facing inwards; on the lower sash it faces outwards. The fit should be snug to prevent heat loss.

6.Staff Bead: A moulded piece of timber made up of four sections, nailed all around the BOX FRAME, which aids airtightness and also holds the bottom sash in place. The staff bead is removable, but rarely salvageable, for the maintenance of the sashes.

7. Meeting Rails: The horizontal framing members which meet the two sashes together in the middle. Their adjoining faces are bevelled so they close together tightly.

8. Stile: Vertical side framing member of a sash — there is one each side.

9. Apron: A decorative panel or cladding beneath the window.

10. Cill: A horizontal board fitted internally at the base of the sashes. Shaped so that water flows away outside.

11. Bottom Rail: The bottom horizontal framing member of a sash.

12. Weight: A pair of lead weights hung on the SASH CORD counterbalance each sliding sash. The sash and weights must weigh the same.

13. Wag Tail: A strip of timber inside the BOX FRAME that separates the WEIGHTS. Also known as a ‘parting slip’.

14. Timber Linings: The sections that form the casings of the BOX FRAME – which must be hollow to house the WEIGHTS – are made in three parts: the ‘outer’, ‘inner’ and ‘pulley’ linings.

15. Pulley Wheel: A pulley mortised into the top of the PULLEY LINING; the SASH CORD passes over it to counterbalance the WEIGHTS. Cheaper pulleys have plain axles; better quality ones are made with roller or ball bearings.

16. Glazing Bar: A vertical or horizontal framing member that divides the panes within the STILES and RAILS. Each is rabbeted – a cut which forms a groove – to hold the single-paned glazing. The quintessential Georgian sash window has ‘six over six’ panes, but other configurations were seen over time.

17. Soffit Lining: The window’s head is made up of the main inner and outer TIMBER LININGS as well as a separate soffit lining; glued triangular blocks provide strength.

NB: A ‘sash’ is a single glazing frame. The full name of a sash window is a ‘vertical double-hung box-framed sliding sash window’.