Draughtproofing is the highest return work in this domain per pound spent, and it is almost entirely unskilled. It is also the one where enthusiasm does real harm, because a house that has been sealed too well and ventilated too little gets damp, and a house with a burning appliance in it can get considerably worse than damp.
So the whole page is built around one distinction: seal the gaps nobody designed, and leave alone the holes somebody did.
Find them before you buy anything
Do this on a cold, windy day, with all the external doors and windows shut.
- A candle or an incense stick, held a hand's width from the edge of doors, window frames, skirtings, loft hatch, letterbox and sockets on external walls. Watch the flame or the smoke lean.
- The back of a damp hand works surprisingly well and needs nothing.
- Turn on the extractor fans and the cooker hood and shut the internal doors. That depressurises the house slightly and makes every leak pull harder.
- Write down what you find, room by room, and rank it by how big the movement was.
You will find that the leaks are not evenly distributed and are not where you expected. In most British houses a handful of openings account for the bulk of it, and half of them are on the ground floor near the front door.
The order to work in
Work down that list and stop when you reach the section headed "what must stay open".
Doors
The front door is usually the worst thing in the house, because it has four edges, a letterbox, a keyhole and a threshold, and every one of them is a gap.
- Letterbox brush or flap, fitted inside. A few pounds, five minutes, and it closes a rectangular hole straight to the street.
- Keyhole escutcheon with a cover.
- Foam or brush strip around the frame. Foam is cheapest and lasts a season or two; EPDM rubber or brush lasts years and is worth the difference.
- A threshold brush strip or draught excluder at the bottom. This is often the single largest gap in the building.
- A curtain over the door, heavy, to the floor, is the traditional answer and it works, particularly on a door that opens straight into a living room.
Internal doors matter too once you are heating one room. See make one warm room: the doors between the warm room and the rest of the house are now buffers and each one is worth stripping.
Do not strip a door so tightly that it will not close, or that it needs a shove. A strip that is compressed permanently goes flat and stops working, and a door that does not latch is a security problem.
Windows
Only the opening parts leak. A fixed pane in good putty or a sealed unit does not, and the draught you feel near a large window is usually cold air falling down the glass rather than air coming through it. That feels identical and is fixed by curtains rather than by strip.
- Draught strip in the rebate of every opening casement.
- Sash windows are their own subject: brush strip in the staff bead and parting bead, and a sash that has been painted shut is already draughtproof.
- Cold air falling off glass is solved by lined curtains, closed at dusk, hung so they sit close to the wall at the top and are not tucked behind a radiator.
- Secondary glazing, even a cheap film shrunk with a hairdryer, makes a large difference on a single-glazed window and costs very little.
Open a window on purpose, twice a day, for ten minutes. That is not a contradiction of this page; it is the point of it. Controlled ventilation that you choose is what makes it safe to remove the uncontrolled ventilation that you did not.
Floors
A suspended timber ground floor is ventilated underneath by design, and the gaps between the boards are not part of that design.
- Fill the gap between the skirting and the floor with a flexible sealant or a timber bead. This is often the biggest leak in a room and it is invisible.
- Fill between the boards with a proprietary filler strip, a bead of flexible sealant, or slivers of timber. Do not use a rigid filler that will crack out as the boards move.
- A rug or carpet with underlay does a great deal on its own.
- Do not block the underfloor airbricks. They keep the joists dry and rot-free, and covering them is a slow expensive mistake. This is on the list below for a reason.
A solid concrete floor does not leak air, so if the ground floor is concrete this whole section is unnecessary.
Chimneys
An open unused flue is a permanent hole to the sky, and it pulls warm air out of the room continuously.
- A chimney balloon or a chimney sheep blocks it, and both are removable, which is the essential property.
- Label the fireplace. A card or a tag hanging in the opening saying the flue is blocked, so that nobody lights a fire under it. This is not optional.
- Leave a small amount of ventilation if there is any damp risk, which most sheep and balloons provide by design.
What must stay open
If a vent is genuinely in the wrong place, blowing directly onto a chair or a bed, the answer is to fit a hit-and-miss cover you can partly close, or to move where the chair is, not to seal it.
Where to stop
The honest limit of this page is that a house needs a certain amount of air change, and past a point you are trading heat for moisture and air quality.
Signs you have gone too far:
- Windows streaming with condensation in the morning where they did not before.
- A musty smell that was not there.
- Black mould appearing in corners, on window reveals, or behind furniture on outside walls.
- Anyone in the house getting headaches or feeling stuffy, particularly in a room with an appliance.
All of those mean open something back up. See damp and mould, which is the other half of this subject and should be read alongside it rather than after the problem appears.
The right target is controlled ventilation, not no ventilation: the house sealed against the leaks you did not choose, and aired deliberately twice a day for ten minutes on your terms.