The new H1 code in the NZ Building Code (NZBC) calls for increased insulation, but more insulation doesn’t always mean better performance. The type and placement of insulation are just as important as the quantity.

There are two main types of insulation:

Closed-cell insulation: Dense, rigid, and highly resistant to air and moisture movement.

Open-cell insulation: More breathable and flexible, allowing some vapour permeability.

If insulation is placed in the wrong location within the structure, it can cause the critical temperature (dew point) to occur in the wrong place. This can lead to:

• Moisture getting trapped inside walls or roofs.
• Mould growth and structural damage due to prolonged exposure to moisture.
• Insulation slumping, reducing its effectiveness.
• Unhealthy indoor conditions, including musty odours and poor air quality.

The Key: Balanced Ventilation + Properly Placed Insulation

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To prevent these issues, insulation must be correctly located relative to the airtightness layer. Balanced ventilation with energy or heat recovery, combined with appropriately placed insulation (whether open or closed-cell), is key to preventing dew point issues that can lead to moisture problems.

Many New Zealand homes are built with little attention to airtightness. Even when a Mechanical Heat Recovery Ventilation (MHRV) system is installed, it can be ineffective if the home is leaky. Here’s why:

• Uncontrolled Air Infiltration: Traditional NZ homes allow air to enter and escape through gaps and cracks, making it impossible to control moisture and temperature effectively.
• Moisture Accumulation: Without airtight construction, HRVs or ERVs can’t properly manage humidity levels, leading to mould growth and condensation issues.
• High Energy Consumption: Leaky homes force heating and cooling systems to work harder, increasing energy use and bills.
• Poor Indoor Air Quality: Drafts bring in pollutants, allergens, and unfiltered outdoor air, leading to unhealthy living conditions.

Airtightness is not a synonym for ‘suffocation station’.

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Airtightness is not a synonym for ‘suffocation station’. Mechanical systems become the lungs of the home. The home ‘breaths’ like we would hope when we leave the windows open and the natural air in. However, it is controlled breathing. Taking out pollens and pollutants, and reconfiguring the energy within the home. Keeping it warm in winter and cool in summer, without needing to condition the new air we are introducing.

The old way of building—where homes rely on natural air leakage rather than controlled ventilation—is no longer sustainable. An airtight home with a well-designed HRV or ERV system offers:

• Better moisture control, preventing mould and structural damage.
• More stable indoor temperatures, reducing heating and cooling needs.
• Significant energy savings, cutting down on energy consumption and carbon footprints.
• Healthier indoor environments, ensuring fresh, filtered air for occupants.

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