Draughts at the old windows

The first cold evening of the autumn finds every leak in the house. A curtain moves with the window shut, a candle on the sill leans one way, and the floor under the window is noticeably colder than the middle of the room. Late September, with the heating just on, is the right time to deal with it, before anyone has to.

Two kinds of cold

Not every chill by a window is a draught. Old glass is cold glass, and the air against it cools, sinks and runs across the floor. In Swedish this has its own word, kallras, and Energimyndigheten describes it exactly as it feels: cold feet and a draught along the floor. The agency puts the loss through older two-pane windows at up to a third of a house’s heat. No strip fixes that part. A heavy curtain drawn at night does help, as does a blind let down after dark.

The other kind is real moving air, coming in round the sash. That part is cheap to fix.

Finding the leak

Close the window properly, catches and all. Then run the back of a hand slowly round the edge of each sash, or hold a lit candle a few centimetres off the joint and watch the flame. A sheet of paper shut into the window and pulled is the other test: where it slides out with no resistance, the strip has gone.

Old double-casement windows usually fail in the same places. The bottom rail, where condensation sits. The corners on the hinge side. And the meeting point of the two sashes, where one closes over the other.

Strip, not tape

The fix is a new rubber strip between the sash and the frame, which Boverket names as the simplest improvement to a window. Pull the old strip out completely, flattened foam and all, and scrape the groove or rebate clean. Self-adhesive profiles come in several shapes for different gaps, so close a scrap between sash and frame first: it should compress, and the window should still shut without a shove. Tape over the joint does stop air, but it comes off in spring with the paint.

If the sash is being repainted at the same time, do it before the strip goes in, and leave the brush hanging in thinner between coats.

The door

The front door has a gap at the bottom that no rubber strip on the frame will reach. A brush or rubber sweep screwed to the inside face of the door, just clear of the threshold, closes it. A curtain on a rail inside the door is the old answer, and it still works.

The vents stay open

In an older house with natural ventilation, some of the fresh air was always meant to come in through those leaks. Boverket warns that after sealing, the supply of incoming air has to be checked so the air indoors does not go stale. So the small vents above the windows stay open. The same goes for anything built round a radiator: the radiator cover in the hall got its row of holes so the warm air could still rise out.