Should I seal all the draughts in my house?
It is tempting to seal every draught you can find, but doing so without thinking about ventilation can cause as many problems as it solves. The right goal is not a hermetically sealed house — it is to stop uncontrolled, wasteful leakage while keeping the controlled fresh-air supply a home needs. This guide explains the balance, and how to seal safely.
Reviewed by George Sora, Certified Passive House DesignerUpdated June 2026Quick answer & key takeaways
7 min read- Sealing draughts is good, but only alongside adequate controlled ventilation.
- A home needs fresh air to remove moisture, carbon dioxide and indoor pollutants.
- Stopping leakage without ventilation can raise humidity and cause condensation and mould.
- The principle is 'build tight, ventilate right' — seal the random leaks, provide deliberate ventilation.
- Never block purpose-provided ventilation such as trickle vents or extract fans.
- Biggest misconception: the more airtight, the better, full stop. Airtightness and ventilation go together.
- Retrofit IQ's approach: measure airtightness and ventilation together so the home is both efficient and healthy.
What this usually means
Draughts are uncontrolled air leakage, and stopping them saves energy and improves comfort. But a house also needs a steady supply of fresh air to stay healthy — to carry away the moisture from cooking, washing and breathing, to dilute carbon dioxide, and to remove cooking smells, volatile compounds and other indoor pollutants. In a leaky house, some of that fresh air arrives accidentally through the draughts, wastefully and unpredictably. When you seal the draughts, you remove that accidental ventilation, so you have to make sure deliberate ventilation takes its place.
If you seal everything and provide no controlled ventilation, the moisture you generate every day has nowhere to go. Indoor humidity rises, surfaces that were previously dried by leakage now stay damp, and condensation and mould can appear or worsen — sometimes in homes that were previously fine. This is the trap behind the idea of sealing every gap: airtightness without ventilation trades draughts for damp.
So the honest answer to 'should I seal all the draughts?' is: seal the uncontrolled ones, but never the purpose-provided ventilation, and add controlled ventilation as the home becomes tighter. Trickle vents, extract fans in kitchens and bathrooms, and in tighter homes a mechanical ventilation system, deliver fresh air deliberately and efficiently — far better than relying on draughts. Done this way, you get the comfort and efficiency of an airtight home without the moisture problems.
Common causes
Sealing without adding ventilation
Closing every leak while leaving no deliberate fresh-air supply lets indoor humidity build up, risking condensation and mould.
Blocking trickle vents
Taping over or closing window trickle vents removes purpose-provided background ventilation and raises humidity.
Disabling extract fans
Switching off or removing kitchen and bathroom extract leaves the wettest rooms without their moisture removal.
Over-sealing a previously leaky home
A home that relied on draughts for its air can develop damp quickly when sealed without a ventilation plan.
Ignoring combustion air
Open-flued appliances need air to burn safely; over-sealing without accounting for this can be hazardous and must be assessed.
Signs and symptoms
Condensation appearing after sealing
Windows misting and surfaces dampening soon after draughtproofing indicate ventilation was lost along with the leaks.
Stuffy or stale air
Air that feels stuffy, or lingering smells, suggests too little fresh air is now reaching the rooms.
New or worsening mould
Mould appearing where there was none can follow over-sealing that traps moisture indoors.
Rising humidity readings
Persistently high relative humidity after sealing shows the home needs deliberate ventilation to remove moisture.
What most people check first
- Whether the home has working trickle vents and extract fans before sealing.
- Whether any open-flued appliances need combustion air.
- How humidity behaves after sealing — rising humidity signals a ventilation shortfall.
- Which draughts are uncontrolled leakage and which are purpose-provided ventilation.
What most people miss
- That a home needs controlled ventilation, so not every opening should be sealed.
- That purpose-provided vents and extract fans are there for a reason and must be kept.
- That over-sealing without ventilation can cause condensation and mould.
- That airtightness and ventilation must be designed together, not in isolation.
The building physics
Ventilation exists to manage the by-products of living in a home: water vapour, carbon dioxide and a range of pollutants. A household generates several litres of water vapour a day through cooking, washing, drying and breathing, and that moisture must be removed or it raises indoor humidity. The higher the humidity, the warmer a surface has to be to stay above the dew point — so a humid, under-ventilated home condenses on surfaces that would have stayed dry in a drier one. Ventilation is therefore not optional; it is half of the moisture balance, the other half being surface temperature.
In a leaky house, ventilation happens partly by accident through the draughts, which is wasteful because it is uncontrolled and dumps heat. Airtightness work removes that accidental ventilation, which is exactly the point — but it means the deliberate ventilation must be adequate to take over. This is the meaning of 'build tight, ventilate right': reduce the random leakage to a low, measured level, and provide controlled ventilation sized to the home's needs, so fresh air is delivered efficiently and moisture is removed reliably.
Controlled ventilation also performs better than draughts ever could. Trickle vents provide background air; extract fans remove moisture at source in kitchens and bathrooms; and a balanced mechanical ventilation system with heat recovery (MVHR) supplies filtered fresh air to living spaces while recovering most of the heat from the air it extracts. In a tight home, MVHR can deliver continuous fresh air with minimal heat loss — something a draughty house, leaking heat through every gap, can never achieve. The combination of good airtightness and good ventilation is what makes a home both efficient and healthy.
How to seal draughts safely
Seal the uncontrolled leakage, keep the purpose-provided ventilation, and add controlled ventilation as the home tightens. That balance gives you comfort and efficiency without moisture problems.
- 01
Identify controlled vs uncontrolled openings
Distinguish purpose-provided ventilation — trickle vents, extract fans, combustion air — from accidental leakage. Seal the leakage, never the deliberate ventilation.
- 02
Seal the uncontrolled leaks
Close floor junctions, penetrations, the loft hatch and window and door gaps, reducing wasteful, weather-driven leakage.
- 03
Keep and maintain background ventilation
Ensure trickle vents are open and working and extract fans are functioning in the kitchen and bathrooms.
- 04
Add controlled ventilation where needed
In tighter homes, provide continuous extract or balanced MVHR so fresh air is supplied and moisture removed efficiently.
- 05
Monitor humidity
Check that indoor humidity stays in a healthy range after sealing; if it rises, the ventilation needs strengthening.
- 06
Assess combustion safety
Where open-flued appliances exist, confirm they still have adequate air after sealing, for safety.
How to prevent it coming back
- Never block trickle vents or disable extract fans when draughtproofing.
- Plan ventilation before, not after, sealing a previously leaky home.
- Monitor humidity and adjust ventilation if it climbs after sealing.
- Account for combustion appliances that need air to burn safely.
- Consider MVHR when targeting high airtightness, so fresh air and heat recovery come together.
How Retrofit IQ investigates this
We assess airtightness and ventilation together, so sealing improves efficiency without compromising air quality or safety.
Do not spend money fixing symptoms before you understand the cause — investigate first, then build with confidence.
Do I need a professional investigation?
Assess airtightness and ventilation together before any significant sealing programme, especially in a previously leaky home, and whenever condensation or stuffiness appears after draughtproofing. Measuring both ensures you seal safely — stopping waste without creating a moisture or air-quality problem.
It is particularly important before aiming for high airtightness or installing MVHR, where the two must be designed as a pair so the home is both efficient and healthy.
Where to go next
Relevant services
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From the Academy
- Airtightness and condensation risk — why leaky buildings rot from the inside.
- Trickle vents and background ventilation — what they do, and don't.
- What is airtightness? ACH₅₀, air permeability and 50 Pa explained.
- Ventilation and mould prevention — the humidity connection.
- Extract ventilation explained — intermittent, dMEV and MEV.
Related case studies
Frequently asked questions
Should I seal every draught in my house?+
Seal the uncontrolled leaks, but keep the purpose-provided ventilation such as trickle vents and extract fans. Sealing everything without ventilation can cause condensation and mould.
Can draughtproofing cause damp?+
Yes, if it removes ventilation without replacing it. When accidental leakage is sealed but no controlled ventilation is provided, indoor humidity can rise and condensation can form.
Why does my house need ventilation if I want it airtight?+
Because a home produces moisture, carbon dioxide and pollutants that must be removed. An airtight home ventilates deliberately and efficiently instead of through wasteful draughts.
Should I close my trickle vents to stop draughts?+
No. Trickle vents are purpose-provided background ventilation. Closing them raises humidity and can cause condensation; seal the uncontrolled leaks instead.
What does 'build tight, ventilate right' mean?+
It means reducing uncontrolled air leakage to a low level while providing good controlled ventilation, so the home is efficient and comfortable and still has plenty of fresh air.
Is it safe to seal a house with a gas fire?+
Open-flued appliances need air to burn safely, so sealing must account for their combustion air. This should be assessed before significant airtightness work.
How do I seal draughts without causing problems?+
Identify and seal the uncontrolled leaks, keep all purpose-provided ventilation, add controlled ventilation as the home tightens, and monitor humidity to confirm it stays healthy.
Stop guessing — find the real cause
Do not spend money fixing symptoms before you understand the cause. Every home behaves differently, and the only reliable way to know what is happening in yours is professional building performance diagnostics. At RetrofitIQ we verify buildings using the right combination of investigations:
- Thermal imaging
- Blower door testing
- Moisture & dew point readings
- Ventilation review
- Building physics assessment
- Passive House methodology