If your lounge feels cold near the windows even with the heater running, or a curtain drifts when no window is open, you are feeling draughts. Draught proofing is the work that stops them. It is one of the cheapest things you can do to an old house, and on timber sash windows it is a job you can do yourself with a screwdriver and an afternoon.
What draught proofing actually is
Draught proofing means closing the small gaps around a window or door so that air stops moving through them. A draught is just air leaking through a gap that should be closed. Warm air you have paid to heat leaks out, cold air leaks in, and the room never quite settles at the temperature you set.
The fix is to fit seals into those gaps. On a double hung sash window the sashes still need to slide, so the seals have to close the gap while letting the window move. That is the part people get wrong when they reach for foam tape or silicone, which either jams the window shut or falls off within a season. Proper draught seals sit in the gap and stay there while the sash runs past.
Draught proofing is not double glazing. It deals with air leaks, not with heat passing through the glass itself, and in most old houses the air leaks are the bigger and cheaper problem. That is why sealing gives so much for so little.
Where the cold gets in
On a typical double hung sash window there are four places air moves through. The first is the gap between the bottom sash and the sill. The second is the meeting rail, the horizontal join in the middle where the two sashes overlap. The third and fourth are the two sides of each sash, in the channels the sashes slide up and down in.
You can find them without any special gear. On a windy day, run the back of a damp hand around the edges of a closed window and you will feel the cold streams. Windows that rattle in the wind are telling you the same story: a sash loose enough to rattle is loose enough to leak.
Doors leak too, mostly at the bottom and around the sides where the door meets the frame. The principle is the same, close the gap without stopping the door from opening.
What it does for heating bills
Heating a room is a losing battle if the warm air keeps escaping and being replaced by cold. Close the draughts and the heater does less work to hold the same temperature, so it runs less and costs less.
The comfort difference is usually the thing people notice first. A sealed room holds its warmth more evenly, the cold patch by the window disappears, and you stop feeling the moving air on your skin. A draught on your ankles makes a room feel several degrees colder than the thermostat says, so you turn the heating up to compensate. Stop the draught and you can often turn it back down. For the wider picture of how sealing fits with insulation and glazing, our guide to improving the energy efficiency of your home covers where your money goes furthest.
Seal types in plain English
There are three main kinds of draught seal, and each suits a different gap.
Brush seals
A brush seal is a strip of dense nylon pile, like a tidy paintbrush laid on its side, held in a carrier. The bristles fill the gap but flex out of the way as the sash slides past. They are the workhorse for the sliding sides of a sash window, and they cope with the small inconsistencies of an old timber window that has moved over the decades.
Compression seals
A compression seal works by being squashed. When the window or door closes, it presses against the seal and flattens it, and that flattened seal blocks the air. This suits places where two surfaces come together and stay put, such as the meeting rail of a sash or the closing edge of a door. It gives a very tight seal, but only where there is a firm closing action.
V-seals
A V-seal is a folded strip, often plastic or metal, that springs open into a V shape. One side sticks to the frame and the other presses against the moving part. It is springy and forgiving, so it suits the sides of sashes and doors where the gap varies, and it is thin enough for gaps too tight for a brush.
Most windows end up with a mix: brushes on the sliding channels, a compression seal at the meeting rail, and the right seal at the sill. Our rundown of draught seals for double hung sash windows goes through the ones that actually last.
What the work looks like
Before you decide whether to take it on, this video walks through a full job on a double hung sash window, from removing the beads to fitting the seals and rehanging the sash.
For the full written steps that go with that video, see our guide on how to draught proof a double hung window.
DIY or trade
Draught proofing a sash window is well within reach of a confident home handyperson. The tools are basic and the seals come in kits sized for common windows, so the hardest part is being patient rather than skilled. A kit like the draught sealing kit for a double hung window on cords gives you the seals and carriers for one window in the right sizes, so you are not guessing at the hardware. There are matching kits for casement and awning sashes and for a single wooden door if your draughts come from those instead.
There are good reasons to bring in someone who does it for a living. If your sashes are painted shut, the cords are broken, or the timber is rotten, those problems are better sorted before or alongside the sealing, and a specialist can do the lot in one visit. Either way the seals are the same, so the money you spend on quality hardware is not wasted.
FAQ
What is draught proofing?
Draught proofing is the work of closing the small gaps around windows and doors so air stops leaking through them. On a sliding sash window it means fitting seals that close the gaps while still letting the sashes slide up and down.
Does draught proofing actually save money?
Yes, by stopping warm air escaping and cold air leaking in, your heater does less work to hold the same temperature. The comfort improvement is usually noticeable straight away, and because a draughty room feels colder than it is, sealing often lets you turn the heating down.
Is draught proofing the same as double glazing?
No. Draught proofing stops air leaking through gaps, while double glazing reduces heat passing through the glass itself. In most older homes the air leaks are the larger and cheaper problem, which is why draught proofing gives such good value.
Can I draught proof sash windows myself?
Yes, a straightforward double hung window is a realistic afternoon job with a screwdriver and a draught sealing kit sized for that window. Windows that are painted shut, have broken cords or rotten timber are worth sorting out first, and a specialist can handle those along with the sealing.
Will draught seals stop my window from opening?
Properly fitted draught seals are made to let the sash slide while closing the gap, so the window still opens and closes normally. Foam tape and silicone are the ones that jam a window or fall off, which is why purpose made brush, compression and V-seals are used instead.