Home Ventilation: Why It Matters and How to Improve It

Ventilation is one of the most misunderstood aspects of home comfort and building health. As UK homes have been made progressively more airtight in the name of energy efficiency — better insulation, double glazing, draught exclusion — many have become under-ventilated. The result is condensation, mould growth, elevated CO2 levels, and poor indoor air quality. The building regulations that require energy efficiency also mandate adequate ventilation — the two must be balanced.

Older UK homes were ventilated by accident — draughts through letterboxes, gaps around window frames, open chimneys, and suspended timber floors with airbricks. As these gaps have been sealed by successive energy efficiency upgrades, the incidental ventilation that kept moisture and CO2 levels manageable has been removed without a deliberate replacement. The consequence is homes that are tighter, warmer, and damper than they were 30 years ago.

Part F of the Building Regulations covers ventilation requirements. For dwellings, it specifies minimum whole-dwelling ventilation rates, extract ventilation requirements for kitchens and bathrooms, and purge ventilation (the ability to fully air a room through openable windows). When undertaking renovation work that affects the building envelope — new windows, insulation, loft work — Building Control will expect ventilation requirements to be addressed as part of the project.

There is no point insulating a home to EnerPHit standard if you do not provide adequate mechanical ventilation. Mould growth, moisture damage, and unhealthy CO2 levels are the inevitable result of prioritising airtightness without ventilation.

— Passivhaus Trust

Passive ventilation relies on natural airflow through trickle vents in windows and passive roof vents. Intermittent extract fans in kitchens and bathrooms remove moisture at source. Continuous mechanical extract ventilation (MEV) runs fans in wet rooms continuously at a low rate with boost when needed. Mechanical ventilation with heat recovery (MVHR) is the gold standard for airtight homes — it supplies fresh filtered air to habitable rooms while extracting stale air from wet rooms, recovering up to 90% of the heat from the extract air before it is expelled.

Before investing in a ventilation system, establish where moisture is being produced and whether existing ventilation is working. Check that trickle vents are open (many homeowners close them), that extract fans are operational and ducted to outside (not into the roof void), and that airbricks below suspended floors are clear. Adding a whole-house positive input ventilation (PIV) unit in the loft is a cost-effective intervention for many homes — it draws fresh air from the loft space and gently pressurises the house, pushing moist stale air out through gaps. Cost is typically £300-£600 installed.

• Check trickle vents are open — many are needlessly closed
• Ensure kitchen and bathroom fans duct to outside, not into the loft
• Check airbricks below suspended floors are clear and unblocked
• PIV (positive input ventilation) is a cost-effective intervention for condensation problems
• MVHR is best for very airtight new build or deep retrofit projects
• Fresh air at night improves sleep quality — a ventilation benefit beyond moisture management