New Zealand’s older homes represent a major opportunity to improve energy efficiency, health, and durability. Despite being among the most expensive in the world, many public and private homes remain poorly insulated and full of hidden air leaks—leading to wasted energy, condensation, and unhealthy indoor air.
Historically, upgrading these homes meant expensive and disruptive renovations. But now, a simpler, more cost-effective approach is available, one that tackles the core cause of heat loss and moisture problems: airtightness.
According to research from the IECC and ENERGY STAR, air leakage is the single biggest source of heat loss in homes—more than walls, windows, or ceilings. Yet it’s often overlooked. By improving airtightness, homeowners can dramatically boost energy efficiency without the high cost and disruption of removing wall linings to retrofit insulation.
Source: Based on data from a NEHERS presentation, ANSI/RESNET Conference, November 2023 and ENERGY STAR publications.
BRANZ researchers conducted a real-world study by upgrading an older home to meet current code standards, then systematically improving its airtightness while maintaining a steady indoor temperature of 20°C. Their results were striking: reducing air leakage from 9 to 1 ACH50 cut heating energy use by 50%. When combined with heat recovery ventilation (MVHR), total energy savings reached an impressive 90%
The data alongside is from BRANZ Bulletin 698 – Residential Mechanical Ventilation Systems.
BRANZ measured energy usage while maintaining 20o C in a 90 m2 Wellington house at different airtightness levels
Proven results: Beyond energy savings, these improvements contributed to a more stable indoor environment, fewer issues with internal moisture, and better control over temperature and airflow—all without the need for extensive demolition or insulation upgrades.
“We are still seeing mould and damage in the wall cavity even after the exterior is made watertight. You need to work just as hard to keep moisture travelling into the wall cavity from the inside – and that’s where envelope sealing comes in.”
MATTHEW CUTLER-WELSH, NZ GREEN BUILDING COUNCIL
When to air seal?
For new builds
For renovations and retrofits
The process is the same but more set up time is required if there are carpets, furniture and cabinetry etc to cover.
In practice, the stage of installation can be varied for both new builds and renovations. It won’t affect the outcome but may affect the setting up process which could be reflected in the cost.
The AeroBarrier air sealing system uses verified software that accounts for the build’s many variables, such as square metreage, number of windows, doors, and bathrooms.
The software combines with an industry standard blower door, which meets ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) standards, to deliver measurable results.
Our software was built to create the highest level of accuracy in your air sealing report.
With AeroBarrier, there’s no question of whether or not you pass inspection. The system updates every 90 seconds and tracks in both ACH50 and (L/s (litres per second) to accommodate different air requirements
Our certificate provides you with the satisfaction and confidence of knowing that you met your requirement. No other air sealing method out there can provide this reliability.
NZGBC accepts the AeroBarrier certificate as part of the Homestar certification process
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