Draughty sash windows: what to check before replacing them

A draught through an old sash window does not automatically mean you need a new window. First work out where the air is coming in. A loose meeting rail, worn seals or a sash that no longer closes squarely may be repairable. If the timber is decayed or the whole frame has moved, the job needs a closer inspection. Take notes before asking for quotes, so each person is pricing the same problem.

Scotland has plenty of sash and case windows that have already lasted generations. Historic Environment Scotland recommends repairing and improving original windows where possible. That is a useful starting point, especially in a tenement or older stone house. It is not a promise that every window can be saved.

Find the gap without taking the window apart

On a windy day, close and lock the window, then move your hand slowly around the inside edge. You may feel air at:

• The meeting rail, where the upper and lower sashes meet. Check whether the catch pulls them snugly together or they still rattle.
• The sides of a sliding sash. A loose fit or worn draught seal can let air through even when the window moves normally.
• The bottom rail or sill. See whether the sash closes fully and whether paint, dirt or a damaged part is holding it up.
• The edge of the window case against the wall. A gap here is a different job from sealing the moving sash; ask the joiner to identify its cause before filling it.

Also note whether both sashes open, close and stay where you leave them. A window that drops, jams or will not lock needs more than a strip of seal. Take a photo of each gap and a short video of any rattle. You do not need to lean out, remove glazing beads or disturb the sash cords to gather useful evidence.

If there is water on the inside glass in the morning, do not assume the window is leaking rain. Condensation and a draught can occur together, and sealing every gap without thinking about ventilation may make moisture worse. Historic Environment Scotland advises keeping some ventilation, particularly where there are open fires, stoves or gas appliances. Tell the person quoting if you also have persistent condensation or mould.

Ask for the repair in the right order

For an original timber window, a useful quote starts with its condition. Ask a joiner who works on sash and case windows to check the sash fit, cords and weights, catches, putty, paint and exposed timber. A loose catch or worn cord is a different repair from decay in the sill or case. Decay may be hidden, so the final scope can change after closer inspection.

Then ask what a repair and overhaul would include. That might mean easing a sticking sash, repairing damaged sections of timber, renewing cords or hardware, and making the moving parts fit properly. Draught proofing can follow once the window operates well. The Engine Shed’s sash window guide describes brush and other discreet systems, along with secondary glazing where extra comfort is needed.

If cold glass is the main problem rather than air through a gap, ask whether shutters, curtains or secondary glazing would help before ordering replacement frames. A glazier may need to assess broken glass or a proposed glazing change. For a listed building, the details of any change matter as much as the choice of trade.

Compare quotes for the same work

Give each contractor the same photos and ask them to spell out:

1. Which parts they believe are sound, which need repair, and what they cannot assess until the sash is opened up.
2. Whether the price covers one window or a whole room, and whether it includes cords, catches, draught seals, glazing, paint and making good around the case.
3. How they will reach the outside safely if external work is needed, especially above ground floor level.
4. What ventilation will remain after draught proofing, and whether the window will still open and lock properly.
5. Which permissions they expect you to check before work starts.

Do not compare a quote for adhesive strips with one for a full overhaul as if they solve the same fault. If a contractor recommends complete replacement, ask which part cannot reasonably be repaired and what a repair would cost. That gives you a real choice rather than a single price.

Check the building’s status before ordering changes

If your home is listed, or in a conservation area, check with the local planning authority before agreeing to alter or replace the windows. Historic Environment Scotland says changing windows in a listed building will almost certainly need listed building consent. Its sash and case window guidance also warns that secondary glazing and some ventilation changes may need consent. Controls can apply to unlisted flats too; the council can tell you what applies to your address and proposed work.

For an ordinary repair, describe the work precisely when you ask. “Fix a draught” is too vague for either a council officer or a contractor to say what permission may be needed. Keep the reply with your quotes.

If you are ready to find someone, browse Scottish joiners and ask specifically about sash and case experience. You can start with joiners in Edinburgh or joiners in Glasgow. For damaged panes or glazing options, browse glaziers. Our home renovation guide covers the wider order of work and the questions to ask before hiring.