Original sash windows are worth keeping, but on a windy night you can feel why people rip them out. The good news is that most of the cold comes through gaps you can seal in an afternoon, without touching the character of the window.
Find the gaps first
On a blustery day, run a wetted hand or a lit candle slowly around the frame. The flame leans, or your skin prickles, wherever air is getting in. Most draughts come down the sides of the sliding sashes and through the gap where the two meet in the middle.
The right materials
Brush-pile strip is the proper answer for the sliding edges, because it seals while still letting the sash move. The cheap foam tape sold for hinged doors jams a sash solid and tears within weeks.
- Brush strip in the staff and parting beads for the runners.
- A discreet brush or compression seal where the sashes overlap.
- Decorator's caulk in the fixed joint between frame and wall.
Quick wins for tonight
If you are not ready for strip, a heavy lined curtain that sits below the sill, or a simple draught snake on the cill, makes a surprising difference. Secondary glazing film, shrunk tight with a hairdryer, is cheap and almost invisible until spring.
Keep some air moving
Do not seal a room airtight, especially one with a gas appliance or a tendency to condensation. The aim is to stop the howling draughts, not to suffocate the house. A little background ventilation keeps the air fresh and the walls dry.