Sash window terms, in plain words.

Jump to: Parts of the window · Glass and energy · Repair and restoration · Common problems · Planning terms

Parts of a sash and case window

Sash window

The classic British window: two framed panels of glass, the sashes, that slide vertically past each other within the window frame. Sash windows are found in Georgian, Victorian and Edwardian buildings across Scotland. Victorian windows are the most common in Glasgow's tenements and terraces, while Edinburgh has Georgian windows in the New Town, Victorian bays in Marchmont and Bruntsfield, and Edwardian villas in Morningside and Merchiston.

Case (box frame)

The hollow timber frame built into the wall that holds the sashes. It is deeper than a modern window frame because it hides the weights and pulleys inside. In Scotland the whole window is usually called a "sash and case" window after these two parts.

Double hung and single hung

In a double hung window both sashes slide, so you can open the top to let warm air out and the bottom to let cool air in. In a single hung window only the lower sash moves and the upper one is fixed.

Meeting rails

The horizontal rails where the upper and lower sashes overlap when the window is closed. A good fit here keeps out draughts and rain, and it is where the sash fastener sits.

Staff bead

The timber strip fixed around the inside face of the case. It holds the lower sash in place while letting it slide, like a guide rail.

Parting bead

The thin strip of timber running down each side of the case between the two sashes, keeping them apart so they slide past each other.

Sash cords and sash weights

Each sash hangs on cords (sometimes chains, for heavier sashes) that run over pulleys to cast iron weights hidden inside the case. The weights are matched to each sash, so even a large window feels light to open and stays where you leave it.

Pulley wheels

The small wheels set into the top of the case that the cords run over. Sound pulleys make for smooth, quiet operation.

Astragals (glazing bars)

The slim timber bars that divide the glass into smaller panes. "Astragal" is the Scottish term, and keeping or matching the original astragal pattern and thickness matters for any work in a listed building or conservation area. "Muntin" is another name you may see.

Sash horns

The small projections below the meeting rail of the upper sash. They became common in the Victorian period, when larger and heavier panes of glass arrived, because they strengthen the joints of the sash. They are now a detail worth keeping.

Sill (cill)

The bottom of the case, sloped outwards to throw rainwater clear of the wall. As the part that takes most of the weather, it is also the part most prone to rot.

Architrave and facings

The decorative moulded trim around the inside of the window opening, covering the joint between the case and the wall. Styles changed from plain Georgian mouldings to more elaborate Victorian ones.

Scotia

A concave moulding, one of the classical profiles found on window and door trims. When parts are renewed, matching the original mouldings keeps the repair invisible.

Sash lifts and fasteners

The handles on the bottom rail used to raise the lower sash, and the catch on the meeting rails that locks the window. Period brass lifts and fasteners are worth keeping or matching.

Simplex fittings

Hinges that let the lower sash swing inwards so the outside of the glass can be cleaned safely from indoors, which matters for upper floor windows.

Spring balances

A modern alternative to cords and weights, using springs to balance the sash. They can suit newer windows, but in period windows traditional cords and weights are usually the better and more authentic choice.

Glass and energy

Double glazing and sealed units

Two panes of glass sealed together around the edges with a gap between them, filled with air or an insulating gas. Standard units are too thick for traditional sashes, so period windows use slim units. Edinburgh's listed building guidance, for example, describes units 14 mm thick. The edge seals of any sealed unit have a limited life and can eventually fail.

Secondary glazing

A separate, slim glazed panel fitted on the room side of the original window. It keeps the original window untouched while improving warmth and cutting noise, which is why it is often the preferred upgrade for listed buildings. The alternative that keeps a single, traditional looking window is our double glazing upgrade: new double glazed sashes in your original case.

Draught proofing

Sealing the gaps around the sashes so warm air stays in without stopping the window from sliding. We use the Aquamac system, fitted discreetly into the sashes and beads. See sash window draught proofing.

Putty and putty line

Traditional linseed oil putty holds the glass in the sash, finished with a sloped edge that sheds water. When paint fails the putty dries out and cracks, so it needs to be kept painted.

Heritage glass

Glass made to look like old glass, with gentle ripples and reflections, for replacing broken panes in listed and period buildings where modern flat glass would stand out.

Georgian wired glass

Glass with a square wire mesh set inside it, so that if it breaks the pieces are held together. It is common in schools and commercial buildings.

Trickle vents and ventilation

Small vents that let a little air through a closed window to reduce condensation. Many period windows are ventilated simply by opening the top sash slightly, which a ventilation lock allows safely.

Repair and restoration terms

Refurbishment

A complete overhaul: every part examined, worn parts replaced, decayed timber repaired, and the window rebalanced, draught proofed and redecorated so it works as it should. See restoration and repair.

Conservation

Looking after a window's historic fabric: repairing rather than replacing wherever possible, using matching materials and methods, and keeping original glass and details.

Splice repair

Cutting out only the decayed part of a timber and joining in new, matching timber, so the rest of the original window is kept. Done well, the repair is almost invisible once painted.

Resin repair

Consolidating or filling small areas of decayed timber with resin. It suits minor damage; larger decay is better cut out and spliced.

Replacement sills

Where a sill has rotted beyond repair, a new one is made in matching timber and fitted into the case. Sometimes only the front part needs renewing.

Paint stripping and repainting

Removing built up layers of paint that stop sashes sliding, then repainting in thin, breathable coats that protect the timber. Painting sash windows follows a particular order so they are not painted shut.

Pointing

The seal between the window case and the stonework. We rake out the old material and repoint by hand in traditional burnt sand and linseed oil mastic.

Period features

The original details that give a window its character: astragals, horns, mouldings, period glass and brass fittings. Keeping them is at the heart of conservation work.

Common problems

Stuck sash

A sash that will not slide, usually from layers of paint, swollen timber or a window that has been painted shut. It is almost always curable by easing, stripping and rebalancing.

Rattling

Sashes that shake in the wind, normally because the beads have worn or loosened. Adjusting or renewing the beads and fitting draught proofing stops it.

Broken cords and sash drop

A sash that crashes down or will not stay open has usually lost a cord. New cords and rebalanced weights put it right, and it is best done before the cord snaps.

Draughts

Cold air through the gaps around the sashes. Together these gaps can add up to a surprisingly large hole in the wall, and draught proofing closes them.

Wet rot and dry rot

Wet rot softens timber that stays damp, most often in sills and bottom rails, and is usually repaired by splicing. Dry rot is a more serious fungal decay that can spread through a building and needs specialist attention.

Condensation between the panes

Misting inside a double glazed unit means its edge seal has failed. The unit needs replacing; the sash itself usually does not.

Damp

Water getting in around a window, through failed pointing, a decayed sill or cracked putty, leads to peeling paint and rot. Finding and fixing the cause comes before any cosmetic repair.

Planning terms

Listed building

A building of special architectural or historic interest, listed by Historic Environment Scotland in Category A, B or C. Changing its windows, beyond like for like repair, normally needs listed building consent.

Conservation area

An area designated by the council for its special character. Glasgow and Edinburgh each have many, from Dennistoun and Carmunnock to Leith and Corstorphine. Changes to how front windows look may need the council's prior approval.

Listed building consent

Permission from the council to alter a listed building, such as replacing whole windows or fitting new sashes that change the design or glazing, like double glazed sashes. Like for like repairs, including new single glazed sashes made to match the originals, generally do not need it. Our guide to listed buildings and double glazing explains what needs consent and what does not.