Ventilation in High-Performance Homes

Why fresh air is designed, not accidental

Many new homes are more airtight than they used to be, but ventilation strategies have not always kept pace. When fresh air is left to chance, occupants often experience condensation, poor indoor air quality or overheating, even in otherwise well-insulated buildings.

In high-performance construction, ventilation is not an accessory. It replaces leakage and must be designed accordingly.

For a deeper explanation of what airtightness actually means in practice and why it changes how buildings must be ventilated, see The Airtight Case for Passivhaus.

Why airtight homes need ventilation

Traditional homes rely on uncontrolled air leakage for ventilation. Gaps in the building fabric allow stale air to escape and fresh air to enter, often without the occupants realising it.

As airtightness improves, this accidental ventilation disappears. That is essential for thermal performance and comfort, but it also means fresh air must be supplied deliberately. Without a planned approach, moisture, pollutants and carbon dioxide can accumulate, undermining comfort and durability.

The solution is not to make buildings leakier, but to replace accidental ventilation with controlled ventilation.

Ventilation as a whole-house system

In a high-performance home, ventilation operates continuously at low volume. Fresh air is supplied to living spaces, stale air is removed from wet areas and the overall air balance of the home is maintained.

In practical terms, ventilation is responsible for:

• Supplying consistent fresh air to living spaces
• Removing moisture from kitchens, bathrooms and laundries
• Maintaining balanced air pressure across the building
• Supporting indoor air quality without relying on open windows

This approach differs fundamentally from intermittent exhaust fans or reliance on window opening. It prioritises predictability and control under all conditions, including cold weather, heatwaves and smoke events.

Heat recovery and energy performance

Mechanical Ventilation with Heat Recovery is commonly used in Passivhaus (Passive House) buildings because it allows fresh air to be supplied while retaining most of the heat that would otherwise be lost.

The technology itself is less important than the principle behind it. Ventilation is separated from heating and cooling, allowing each system to do its job efficiently without working against the building fabric.

This supports stable internal temperatures and low energy demand without compromising air quality.

Moisture control and durability

Ventilation plays a critical role in moisture management. Indoor moisture is generated continuously through normal occupancy and must be removed in a controlled way.

By maintaining stable humidity levels, continuous ventilation reduces condensation risk and supports material durability. This is particularly important in airtight buildings, where drying potential must be designed rather than assumed.

Good ventilation protects not just comfort, but the long-term performance of the building.

Designed air, delivered on site

As with all performance outcomes, ventilation only works when it is properly installed and commissioned. Duct routing, airtightness, commissioning and ongoing operation all affect how the system performs in practice.

In high-performance construction, ventilation is part of the building fabric. When it is treated as a system rather than an add-on, it supports comfort, health and durability year-round.