The Importance of Mechanical Ventilation in Airtight Homes

The Importance of Mechanical Ventilation in Airtight Homes

In the quest for energy efficiency and sustainability, airtightness is rapidly gaining attention for it’s many benefits and the difference it makes to energy efficiency. The more airtight the home, the less energy it will use. It’s not the only factor, but it’s one of the more important ones.  

Airtightness levels vary significantly across different types of homes, reflecting advancements in building techniques and materials over time. Traditional older homes, particularly those built before the 1980s, often have high air leakage rates, typically around 10 to 20 air changes per hour (ach) at 50 Pascals. These homes, characterized by single-glazed windows, minimal insulation, and drafty construction, allow substantial uncontrolled air flow. In contrast, modern homes built to current New Zealand Building Code standards achieve much lower airtightness levels, averaging around 5 ach50. Homes constructed with advanced techniques and materials, such as those using SIPs like Formance panels, can achieve remarkable airtightness, often down to and below the Passive House standard of 0.6 ach50. These homes, built within the last decade, incorporate high-performance windows, continuous insulation, and meticulous sealing of all joints and penetrations, ensuring minimal air leakage and enhanced energy efficiency.

While this level of airtightness is a significant achievement, it necessitates a comprehensive approach to ventilation to ensure the health and comfort of occupants, as well as the longevity of the building.

Understanding Airtightness and Its Implications

Airtight homes, including those constructed with SIPs, are designed to minimize uncontrolled air leakage, thereby enhancing energy efficiency by reducing the need for heating and cooling. However, this same airtightness can lead to a buildup of indoor pollutants, moisture, and stale air if not properly managed. Traditional homes, with their higher levels of air leakage, naturally expel some of these contaminants, but in an airtight home, mechanical ventilation becomes essential. 

To read more about airtightness read our article titled "why should your new home be more airtight?"  

The Case for Mechanical Ventilation

Mechanical ventilation systems, such as Heat Recovery Ventilators (HRVs) or Energy Recovery Ventilators (ERVs), play a crucial role in maintaining indoor air quality in airtight homes. These systems continuously exchange indoor air with fresh outdoor air, filtering out pollutants and recovering heat from the outgoing air to reduce energy loss.

Types of Mechanical Ventilation Systems

  • Heat Recovery Ventilators (HRVs): These systems extract heat from the stale indoor air before it is expelled outside and use it to warm the incoming fresh air. This process significantly reduces the energy required to heat the home.
  • Energy Recovery Ventilators (ERVs): In addition to heat, ERVs also transfer moisture between the incoming and outgoing air streams. This helps maintain optimal humidity levels inside the home, enhancing comfort and reducing the risk of mould growth.

Health Benefits

According to BRANZ (Building Research Association of New Zealand), proper ventilation is vital for maintaining healthy indoor air quality. Poor ventilation can lead to the accumulation of pollutants such as volatile organic compounds (VOCs), carbon dioxide, and moisture. High humidity levels can encourage mould growth, which poses serious health risks, including respiratory issues and allergies. Mechanical ventilation ensures that these pollutants are effectively removed, providing a healthier living environment for occupants.

For instance, VOCs, which can emanate from building materials, furnishings, and household products, can cause headaches, dizziness, and long-term health problems. Carbon dioxide, while not inherently harmful at low levels, can build up in airtight homes and lead to drowsiness and reduced cognitive function. Moreover, radon, a naturally occurring radioactive gas that can enter homes through foundation cracks, is a known carcinogen. Mechanical ventilation helps mitigate these risks by ensuring a steady flow of fresh air into the home.

Building Health

The New Zealand Green Building Council (NZGBC) emphasizes that mechanical ventilation is not only crucial for occupant health but also for the building’s health. Moisture management is a key factor in preventing structural damage. Without adequate ventilation, moisture from activities like cooking, showering, and breathing can accumulate, leading to condensation on cold surfaces. Over time, this can cause mould growth and damage to building materials, compromising the structural integrity of the home.

In airtight homes, even small amounts of moisture can become problematic. Condensation can form on windows, walls, and other cold surfaces, leading to mould growth and wood rot. Over time, this can degrade insulation, reduce the effectiveness of the building envelope, and lead to costly repairs. Mechanical ventilation systems help maintain balanced humidity levels, preventing these issues and ensuring the longevity of the home.

Energy Efficiency and Comfort

While some may worry that mechanical ventilation systems consume additional energy, the reality is that modern systems are designed to be highly efficient. HRVs and ERVs recover heat from outgoing air, reducing the load on heating systems and thus saving energy. This not only enhances the overall energy efficiency of the home but also contributes to a more comfortable indoor environment. Consistent temperatures and humidity levels are maintained, which are critical for comfort and well-being.

In addition to heat recovery, some advanced ventilation systems also incorporate features such as humidity control and air filtration. These systems can remove excess moisture during humid conditions and add humidity when the air is too dry, maintaining a comfortable indoor environment year-round. Furthermore, high-efficiency particulate air (HEPA) filters can capture allergens, dust, and other airborne particles, improving air quality and reducing the risk of respiratory issues.

Compliance with Standards

In New Zealand, building codes and standards increasingly recognize the importance of mechanical ventilation in airtight homes. For instance, the BRANZ House Condition Survey highlights that mechanical ventilation is recommended for homes achieving high levels of airtightness. Compliance with these standards ensures that airtight homes not only meet but exceed expectations for energy efficiency, health, and sustainability.

The NZGBC’s Homestar rating system, which assesses the health, warmth, and efficiency of New Zealand homes, includes points for effective ventilation systems. Achieving a high Homestar rating not only improves the living conditions for occupants but also adds value to the property. Potential buyers are increasingly aware of the benefits of energy-efficient, well-ventilated homes, making mechanical ventilation a worthwhile investment.

Maintenance of Mechanical Ventilation Systems

To ensure optimal performance and efficiency, regular maintenance of mechanical ventilation systems is essential. This includes cleaning or replacing filters, checking and cleaning the heat exchange unit, and ensuring that the ductwork is free from obstructions. Regular maintenance not only prolongs the lifespan of the system but also ensures that it operates efficiently, maintaining good indoor air quality.

Cost Considerations

While the initial investment in mechanical ventilation systems can be substantial, it is important to consider the long-term economic benefits. Improved indoor air quality reduces healthcare costs by minimizing health issues related to poor air quality. Additionally, preventing moisture-related damage to the building structure can save homeowners from expensive repairs and maintenance.

Energy savings from heat recovery systems also contribute to lower utility bills. In a well-insulated, airtight home, the energy required for heating and cooling is already minimized. By further reducing energy losses through mechanical ventilation, homeowners can enjoy even greater reductions in their energy costs. This makes the initial investment in a ventilation system highly cost-effective over the long term.

Future-Proofing Homes

As climate change continues to impact weather patterns, homes need to be resilient against extreme weather conditions. Airtight homes with mechanical ventilation are better equipped to handle these changes. They provide stable indoor environments that are less affected by external temperature fluctuations, ensuring comfort and safety for occupants.

Moreover, future regulations are likely to become stricter regarding energy efficiency and indoor air quality. By incorporating mechanical ventilation now, airtight homes are future-proofed against these evolving standards, ensuring they remain compliant and desirable in the market.


In conclusion, while the superior airtightness of homes constructed with SIPs or other advanced materials offers significant advantages in terms of energy efficiency and environmental impact, it also necessitates the integration of mechanical ventilation systems. These systems are indispensable for maintaining indoor air quality, ensuring the health of occupants, and protecting the structural integrity of the building. By investing in mechanical ventilation, homeowners can enjoy the full benefits of their airtight, energy-efficient homes without compromising on health or comfort.

Mechanical ventilation is not just a luxury; it is a necessity for modern, airtight homes. It ensures that the homes of today and tomorrow provide safe, healthy, and comfortable living environments, while also being energy-efficient and environmentally responsible.