Why older houses leak
Many older homes were built before airtightness was a design goal. Timber floors move, sash windows have slight clearances so they can slide, doors shrink and swell with the seasons, and old fireplaces and flues were open to the sky. Pipes and cables pass through walls with small gaps around them. Individually these holes seem minor, but together they allow a steady flow of outside air, which pulls warm air out and cold air in.
Sealing the unwanted gaps is often one of the lower-cost and less disruptive efficiency measures, and it can make rooms feel noticeably more comfortable, because moving cold air is what people often experience as a draught. How much energy it saves varies widely between houses, so it is best to see it as a sensible first step and not a guaranteed fix.
Finding the leaks
You can find most draughts without special equipment.
- The hand test. On a windy day, move a dry hand slowly along the edges of doors, windows, skirting boards and around sockets and pipes. Cool moving air is easy to feel.
- The tissue or candle test. Hold a thin strip of tissue near a suspect gap and watch for movement. If you try a flame, take great care and keep it away from curtains and anything flammable. Never use a flame near a gas smell or near a fuel-burning appliance. A stick of incense or a smoke pencil is generally safer.
- Looking from outside. Gaps where cables enter, cracked sealant and missing mortar may be visible.
- A professional test. A surveyor can carry out an air pressure test or use thermal imaging to show where air and heat escape, which is useful in larger projects. Thermal imaging is easier to interpret when there is a clear temperature difference between inside and out.
Common problem areas include:
- Gaps under and around external doors, and keyholes and letterboxes
- Window frames and sash windows
- Gaps between floorboards and under skirting boards
- Loft hatches
- Around pipes where they pass through floors and walls
- Unused chimneys and open fireplaces
- Extractor fans and vents without closers
- Recessed light fittings in ceilings that open into the loft space
Simple fixes
Many jobs can be done as DIY with inexpensive materials.
- Self-adhesive foam or rubber strips around door and window frames. Choose the thickness to match the gap, and apply to a clean, dry surface. Very thick strips can stop a door closing properly.
- Brush or flap seals at the bottom of doors, and a cover for the keyhole.
- Sealant (flexible, paintable types) for small gaps around frames, skirting boards and pipe penetrations. Mastic-style products suit joints that move slightly.
- Gap filler or strips between floorboards, or a flexible sealant in narrow gaps. Lifting the carpet and underlay reveals many of these. Flexible products are generally better than rigid fillers because timber moves.
- Loft hatch seal, usually a compression strip, and an insulated hatch cover.
- A chimney balloon or cap for an unused chimney, with a clear reminder never to block a flue in use.
For sash windows, specialist brush strips can reduce draughts without stopping the window from working. Heritage windows are sometimes protected by regulations if the building is listed or in a conservation area, so check before altering the frames. Secondary glazing and other options are covered in the article on window insulation.
What not to seal
This is the part that deserves the most care. Some openings are deliberate.
- Air bricks and underfloor vents keep timber floor voids dry. Blocking them can cause rot and damp.
- Vents for fuel-burning appliances. Gas boilers, wood burners, open fires and some heaters need a supply of air to burn safely. Blocking it can lead to poor combustion and carbon monoxide.
- Flues and chimneys in use. Never seal these.
- Extractor fans and trickle vents in kitchens and bathrooms, which control moisture.
Poorly ventilated homes can develop damp and mould, a subject covered in the article on condensation control. Poor ventilation can also allow indoor pollutants to build up, which matters for overall indoor air quality. As a rule, if you are unsure whether an opening is deliberate, leave it and ask a qualified heating engineer, builder or surveyor.
If your house has any fuel-burning appliance, fit a working carbon monoxide alarm and have appliances serviced regularly. This is sensible whether or not you do any draught proofing.
Controlled ventilation after sealing
Once an older house is tighter, ventilation becomes something to plan, not leave to chance. Good habits include running the extractor fan while cooking and bathing, opening windows briefly to clear stale air, and using trickle vents where fitted. If you have undertaken more extensive work, particularly in a house that was previously very leaky, a professional may recommend more permanent ventilation provision, and some retrofit projects involve mechanical ventilation.
An order that makes sense
- Check for fuel-burning appliances and note which vents they rely on.
- Do the hand test around the house on a windy day and mark the problem areas.
- Start with the cheapest, highest-impact gaps: doors, loft hatch, letterbox, keyholes and floor edges.
- Move on to windows and pipes.
- Reassess ventilation, particularly kitchens, bathrooms and any room with an appliance.
- Keep an eye on windows and walls for new condensation over the first winter.
Draught proofing usually fits well alongside other work. It is a modest step compared with major projects such as fitting home insulation to a roof or walls, but it is often an easy place to start and can reduce the load on any new heating system.
Renters
If you rent, door strips, draught excluders and removable window film are often possible without altering the property, but ask your landlord before making permanent changes. More on this is covered in the article on renting sustainably.
A cautious note
Savings and comfort improvements differ from house to house, and sealing gaps is only one part of the picture. If you have any doubt about ventilation or combustion safety, get professional advice before blocking anything.