Draught proofing is safe as long as you seal only the accidental gaps and leave every deliberate vent working. If your home is already fairly airtight, or you live in a radon Affected Area, check the ventilation and test for radon rather than sealing everything you can find.
This guide uses the Energy Saving Trust’s (EST) draught proofing and ventilation advice, the government’s guidance on the health risks of damp and mould, and UK Health Security Agency (UKHSA) radon guidance. For costs, products and DIY tips, see our main draught proofing guide.
What is the difference between a draught and ventilation?
A draught is uncontrolled: cold air getting in through gaps around doors, windows, floorboards, loft hatches and unused chimneys. Ventilation is controlled: openings and fans that are there on purpose to let fresh air in and damp, stale air out. The EST puts it plainly — good ventilation is still essential, so you should not block vents, chimneys or airflow needed for safety and air quality. Controlled ventilation helps reduce condensation and damp by letting fresh air in when it is needed.
The aim is to close the first kind of gap and keep the second.
Which vents should you never block?
According to the EST, leave these alone:
- Trickle vents — the small vents above windows. The EST says you should normally leave them open all the time.
- Extractor fans in kitchens, bathrooms and utility rooms, which remove damp air quickly where lots of moisture is produced.
- Wall vents and air bricks. Air bricks below a suspended timber floor ventilate the space underneath and stop the floorboards rotting.
- Ventilation for gas appliances. All flueless gas appliances need some ventilation to work safely, and you must not block fixed ventilation openings needed for flueless or open-flue gas heaters. Take special care if you have internal gas appliances such as a gas hob.
- Rooms with open fires or open flues, which must be adequately ventilated. A chimney draught excluder should not fully block the chimney, and a removable one must come out before you light a fire.
The EST adds a warning that is easy to miss: if your home has no trickle vents, wall vents or mechanical ventilation, it may already be too airtight, and draught proofing may not be suitable. And if your home is already fairly well draught proofed, adding more may increase the risk of poor air quality.
Can draught proofing cause condensation and mould?
It can if it takes away ventilation the home needs. The government’s guidance on damp and mould says condensation is one of the most common causes of damp and mould in homes: moisture from showering, drying laundry and cooking builds up in the air if it cannot escape. It also notes that some energy efficiency work may reduce overall ventilation rates, so it is essential to check — with professional advice where needed — whether ventilation is adequate when you improve energy efficiency.
The same guidance points the other way too: warmer, better-insulated homes are typically less prone to damp and mould, provided ventilation is adequate. Draught proofing is not the problem; draught proofing that seals up the vents is.
This matters for health. The guidance says damp and mould mainly affect the airways and lungs, and estimates that in 2019 damp and mould in English homes were associated with around 5,000 cases of asthma and around 8,500 lower respiratory infections. If you already see black spots on window reveals or in corners, deal with the cause before sealing the room up — this guide to what causes mould in a home, from condensation to leaks is a good place to start.
Does draught proofing affect radon?
Radon is a colourless, odourless radioactive gas that comes from the small amounts of uranium in all rocks and soils. UKHSA explains that buildings naturally draw air in from the ground through cracks and gaps in the floors, and that air contains radon. UKHSA estimates radon causes over 1,100 lung cancer deaths a year in the UK, and the risk is much higher for smokers and ex-smokers.
UKHSA does not publish a figure for draught proofing on its own. But a 2019 study in the journal Indoor Air using Public Health England radon measurements from 470,689 UK homes, found that energy efficiency measures that make homes more airtight were associated with higher indoor radon levels. UKHSA also notes that simple steps such as sealing around loft hatches or sealing large openings in floors do not reduce radon on their own.
So if you live in an area where radon is a concern, the sensible step is to measure, not guess:
- Check whether you are in an Affected Area. UKHSA sells a Radon Risk Report for an address for £3.90 including VAT. You can also read about which parts of the UK are radon Affected Areas.
- Test over three months. UKHSA uses two detectors, one in the living area and one in an occupied bedroom, for three months, because radon levels change from day to day. Its domestic test costs £52.80 including VAT. Results are less reliable while building work is going on, so test once your draught proofing or insulation is finished. More on how a home radon test works and how to read the result.
- Know the levels. UKHSA recommends reducing radon in homes where the yearly average is above the Action Level of 200 becquerels per cubic metre (Bq m-3). Between the Target Level of 100 and the Action Level, it says action should be considered, especially if anyone in the home smokes or used to.
How do you draught proof safely, step by step?
- Find the draughts. Check doors, windows, letterboxes, keyholes, loft hatches, floorboards, skirting boards, unused chimneys and where pipes pass through walls.
- Find the vents too. Note every trickle vent, air brick, wall vent and extractor fan, and any vent near a gas appliance. These stay open.
- Seal the accidental gaps. Strips and brush seals for doors and windows, letterbox and keyhole covers, filler for gaps in floorboards and skirting, and a cap or removable excluder for an unused chimney.
- Keep kitchens and bathrooms ventilated. Use extractor fans while cooking and showering.
- Get help for older or traditional homes. The EST says older buildings often need extra care or specific materials, and a professional is likely to save more energy because they know which materials to use where.
- In a radon Affected Area, test afterwards. A three-month test once the work is done tells you where you stand.
Is draught proofing still worth it?
Yes. The EST says draught proofing windows, doors and floors could save around £55 a year in Great Britain, and professional draught proofing of windows and doors costs around £250 for a whole house; doing it yourself is cheaper. Draught proofing an unused open chimney could save around another £45 a year, with chimney caps from around £150. A draught-free home is also comfortable at a lower temperature, and the EST says turning the thermostat down from 22°C to 21°C could save around £120 a year.
That makes it one of the quickest measures to pay back — see how it compares with insulation in our ranking of insulation measures by payback, and for more low-cost changes, our five quick wins to cut your energy bill.
Frequently asked questions
Can draught proofing cause condensation and mould?
Only if it cuts ventilation the home needs. Seal accidental gaps, keep trickle vents, extractor fans, wall vents and air bricks clear, and check ventilation is adequate when you make a home more airtight.
Which vents should I never block?
Trickle vents, wall vents, extractor fans, air bricks and the fixed ventilation openings needed by flueless or open-flue gas appliances. Do not seal rooms with open fires or open flues.
Does draught proofing increase radon?
There is no UKHSA figure for draught proofing alone, but research on Public Health England data found more airtight homes tended to have higher radon. In an Affected Area, test over three months once the work is finished.
How much does draught proofing save?
Around £55 a year for windows, doors and floors, and around £45 a year for an unused open chimney, according to the EST.
Sources: Energy Saving Trust, draught proofing (updated 20 May 2026) and floor insulation (updated 19 May 2026); GOV.UK, Understanding and addressing the health risks of damp and mould in the home (MHCLG, DHSC and UKHSA); UKHSA’s UKradon pages on radon health risks, the Action and Target Levels, measuring radon and reducing radon levels; Symonds and others, “Home energy efficiency and radon: an observational study”, Indoor Air, 2019. Checked 2 October 2026.