October is when most people find out how draughty their house is. The heating goes on properly for the first time, and within a fortnight there is a room nobody sits in, a hallway that never warms up, and an energy bill that raises eyebrows.
Draught-proofing a UK home is the cheapest meaningful thing you can do to your heating bill. Materials for a whole three-bed house come in well under £150, most of it is a weekend with a tape measure and a caulking gun. Insulation and heat pumps are the bigger prizes, but they cost thousands and take months. This starts working the same evening.
The catch is that two of the gaps in your house are supposed to be there, and sealing them can be dangerous. That part is worth reading twice.
Find the draughts before you buy anything
Cold air does not come from where people think. The window you can feel is rarely the biggest loser; the gap under the skirting behind the sofa often is.
Pick a cold, breezy day, close every window and external door, and turn off the extractor fans and the heating. Walk the house with a lit incense stick, holding it slowly around every edge: window and door frames, letterbox, keyhole, loft hatch, skirting boards, floorboards, top-floor ceiling light fittings, and wherever pipes come through walls. Where the smoke bends, you have a draught. Write it down as you go.
The usual order of guilt in a UK house
Suspended timber floors — gaps between boards and at the perimeter, over a ventilated void
The loft hatch, often an uninsulated, unsealed board sitting in a rebate
Old timber windows and doors, especially sash windows
Unused chimneys and open fireplaces
Letterboxes, keyholes and cat flaps
Service penetrations — under-sink pipework, boiler flue surrounds, extractor ducts
Skirting-to-floor junctions
What each job costs and what it takes
Indicative material costs for a typical three-bed house, DIY unless stated.
Job
Indicative material cost
Time
Self-adhesive foam or brush strip, all windows
£15–£40
2–3 hours
Door brush strip and threshold seal, front and back
£20–£45
1 hour
Letterbox and keyhole covers
£10–£20
20 minutes
Chimney balloon or removable chimney sheep
£20–£35 per flue
15 minutes
Silicone or acrylic sealant, skirtings and frames
£15–£25
2–3 hours
Floorboard gap filler (resin strips or flexible filler)
£40–£90
Half a day
Loft hatch seal and insulation
£15–£30
1 hour
Professional sash window draught-proofing (per window)
£200–£450 fitted
Trade job
Everything above the last line is a DIY weekend. Sash windows are the exception: done properly, the brush seals are routed into the timber, the sashes eased and rebalanced, and the window still opens afterwards. Stuck-on foam strip on a working sash lasts a winter and ruins the operation.
Floors: the one most people skip
If your ground floor is suspended timber — air bricks around the outside of the house, a slight bounce underfoot — the space under those boards is deliberately ventilated to open air. Gaps between the boards are not letting warm air out of a cold room; they are letting outside air straight in.
Flexible filler or resin strips between boards, plus sealant at the skirting perimeter, deals with it. Tedious, and in most Victorian and Edwardian homes the single biggest change you will feel.
Do not block the air bricks in the outside wall while you are at it. They ventilate the void under those floors. Blocking them is how sound joists start rotting quietly for a decade.
The two things you must not seal
This is where draught-proofing stops being harmless.
Rooms with an open-flued appliance. A gas fire, a solid fuel stove, an open fire in use or an older back boiler needs air to burn safely and to draw combustion gases up the flue. Sealing the room too tightly — or blocking a purpose-provided vent — risks incomplete combustion and carbon monoxide. If a room has a fuel-burning appliance in it, get a Gas Safe registered engineer, or a HETAS-registered installer for solid fuel, to confirm what ventilation must stay.
Background and extract ventilation. Trickle vents, wall vents and extractor fans carry moisture out. Modern UK homes are sealed tightly enough that blocking them produces condensation, then black mould on cold external walls, usually by February.
The rule of thumb: seal the gaps nobody designed, leave the ones somebody did.
Will it change your EPC?
Modestly. Draught-proofing is not a headline EPC measure the way loft insulation, cavity wall insulation or a heating upgrade are, and the assessment model gives it limited weight. If your goal is a higher band for a sale or a mortgage product, it belongs on the list but not at the top of it.
If your goal is a house that is comfortable in January without pushing the thermostat up two degrees, it is the best value on the list by a distance.
What to do in the next 30 minutes
Do the incense-stick walk on the next cold day and write down every location, room by room.
Check whether your ground floor is suspended timber — look for air bricks outside, listen for hollowness underfoot.
Identify every fuel-burning appliance and the vents serving it, and mark those rooms off-limits until a registered engineer has looked.
Count your unused chimneys. Each one is a £25 fix and an open hole to the sky.
Order the cheap stuff — brush strips, letterbox cover, sealant — before the first cold snap sells it out.
Keep the list. Draught-proofing gets done in patches over several weekends, and the half you finished in October is impossible to remember by March. Save the draught checklist to Home+ alongside the rest of your home’s record, so next autumn you start from what is left rather than from scratch.
FAQ
How much does draught-proofing actually save a year? The Energy Saving Trust publishes an annual figure for a typical UK home. A draughty Victorian terrace with a suspended floor and three open chimneys will save considerably more than a well-sealed 2015 new build, where there may be very little left to seal.
Is draught-proofing the same as insulation? No. Insulation slows heat passing through a surface — a wall, a roof, a floor. Draught-proofing stops air moving through gaps in that surface. You need both, but draught-proofing costs a fraction of the price and you feel it immediately.
Can I block up an unused chimney permanently? You can, but do it properly. A permanent cap still needs to allow some airflow so the flue does not become damp, and any appliance connected to it must be removed or isolated first. For most people a chimney balloon is the better answer — it works, it costs £25, and it comes out again if you reinstate the fire.
Will sealing my house cause condensation and mould? Only if you seal the ventilation as well as the draughts. Trickle vents, extractor fans and purpose-provided wall vents stay. Moisture has to leave somewhere, and if it cannot, it condenses on the coldest surface you own.
Is it worth paying someone to draught-proof for me? For sash windows, generally yes. For everything else the labour cost usually exceeds the annual saving, and the work is within reach of anyone with a tape measure and a caulking gun.
