Draught-Proofing Your Home: What to Seal and What Not To
Where draughts come from in UK homes, which gaps are worth sealing, which ventilation you must leave alone, and realistic costs for DIY draught-proofing.
Draught-proofing is one of the cheapest home improvements, and one of the easiest to do badly. Done well, it stops cold air creeping in through gaps you never meant to have, so rooms feel warmer at the same thermostat setting. Done carelessly, it seals up ventilation your home needs, causing condensation or even safety risks. The skill is knowing which gaps are accidents and which are there for a reason.
Find the draughts first
Do not buy anything until you know where air is getting in.
- On a windy day, walk round holding a lit incense stick or your wet hand near suspect areas. Smoke bending sideways or a cold sensation shows a leak. Avoid naked flames near curtains.
- Look for daylight around door frames and under doors.
- Check from outside too, as gaps in pointing or sealant are visible.
Typical problem areas include:
| Location | Typical fix |
|---|---|
| Gaps under external doors | Brush or hinged draught excluder |
| Letterboxes | Brush or flap insert |
| Keyholes | Cover plates |
| Window frames | Adhesive foam, rubber or brush strips |
| Gaps between skirting and floor | Sealant or flexible filler |
| Floorboards | Filler strips or sealant between boards, or underlay |
| Loft hatches | Foam strip and a catch |
| Pipework entering walls | Sealant or expanding foam |
| Unused chimneys | Chimney balloon or cap |
Do it in the right order
- Large leaks first: Doors, letterboxes and the loft hatch typically make the most difference.
- Windows second: Fit seals on openers and fill gaps between frame and wall with decorators' caulk.
- Floors and skirting: Fill gaps with flexible sealant that moves with the timber.
- Pipe holes and cable entry: Seal around penetrations, especially under sinks and in the loft.
What not to block
A house needs controlled ventilation to remove moisture and burn fuel safely. Do not block:
- Trickle vents in window frames
- Air bricks and underfloor vents
- Extractor fans in kitchens and bathrooms
- Vents or flues for fires, boilers and stoves or the gap round them
- Chimney vents, unless you fit a vented cap
If you have a gas or solid fuel appliance, ask a qualified engineer about air supply before you seal. See our ventilation guide and carbon monoxide alarm guide.
Costs
Typical DIY costs are modest. Brush and foam strips are a few pounds for a window or door, a tube of sealant a few pounds, and a letterbox brush a similar amount. A weekend's work on a whole house may cost from around £50 to £150 in materials. Having a professional draught-proof a home typically costs more, particularly for sash windows and period features, and varies by region.
Sash windows and period homes
Original sash windows leak around the meeting rail and sides. Specialist brush systems work well and keep the windows operable. Avoid sealing them shut. Listed buildings and conservation areas may have rules about alterations, so check with your local council before changing windows or external features.
Does it actually save money?
The saving varies with how leaky the home is. Older, unrenovated houses usually benefit most. Combine with loft insulation and sensible heating controls for the best effect. See our energy-saving quick wins and heating controls guide.
When it goes wrong
Signs that you have over-sealed:
- New or worse condensation on windows
- Mould on walls or in wardrobes
- A stuffy or musty smell
- Gas appliances or fires behaving oddly, or a CO alarm sounding
If any of these happen, reopen trickle vents, improve ventilation and get appliances checked.
For renters
Most draught-proofing materials are removable or peel-off, so renters can often do it without trouble. Ask permission for anything more permanent, such as sealant on frames, and check your tenancy agreement.
If you want a professional to draught-proof windows or doors, search on Compito, compare ID-verified local providers by postcode and send a request for an offer.
A worked example: a Victorian terrace
A mid-terrace with sash windows, a front door with a letterbox and a suspended timber ground floor is draughty in winter. The owner prioritises the front door and letterbox, fits brush seals to the sash meeting rails and sides, seals the gaps between skirting and floorboards with flexible sealant and fits a cover to the unused fireplace with a small vent. The open fire in the lounge is left alone, with clear air supply. The house feels calmer, and nothing was sealed that needed to breathe.
The check after you finish
- Run the incense test again on the same windy day.
- Look at windows in the morning for new condensation.
- Check that extractor fans, vents and trickle vents are open.
- Test your carbon monoxide alarm if you have fuel-burning appliances.
Products and where they suit
| Product type | Where it suits | Watch for |
|---|---|---|
| Foam strip | Low-cost, small gaps on casements | Wears out sooner |
| Rubber or compression strip | Door and window frames | Needs the right thickness |
| Brush strip | Sashes, sliding parts, door bottoms | Needs a firm fixing |
| Sealant or caulk | Static gaps, frames, skirting | Needs clean, dry surface |
| Secondary glazing | Whole window upgrade | Needs cleaning access |
Check before you fill a gap
If you are unsure what a gap is for, find out before filling it. Ask a heating engineer about flues and air supply and a builder or surveyor about airbricks and underfloor voids. Gas work belongs to a Gas Safe registered engineer.
Frequently asked questions
What is the best place to start draught-proofing?
External doors, letterboxes and the loft hatch usually give the biggest improvement per pound.
Can draught-proofing cause damp?
Yes, if you remove all ventilation. Keep trickle vents and extractor fans working and manage moisture.
Is draught-proofing worth it with double glazing?
Often yes, since double glazing does not stop gaps around frames, doors and floors.