The Hidden Potential in Existing Housing Stock
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.
The Overlooked Energy Saver: 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.
Proven Benefits: The BRANZ Findings
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.
New Zealand has some of the worst respiratory health statistics in the OECD, largely due to cold, damp, and draughty homes. Simply adding wall insulation won’t fix this problem—preventing moist air from entering wall cavities through airtightness is essential.
The Health Cost of Draughty, Damp Homes
48% of New Zealand homes suffer from mould
Potential Energy Use Reduction – 73%
Potential Energy Use Reduction – 100%
“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
How Airtightness Enhances Ventilation Efficiency
Airtightness and mechanical ventilation function as a system. In a leaky home, air bypasses the ventilation system, wasting energy and undermining air quality. In an airtight home, airflow is controlled, enabling efficient heat recovery and delivering fresh, filtered air.
A Breath of Fresh Air
A warm, dry, healthy home is one that breathes continuously, circulating fresh air without relying on open windows or wasting heat, preventing condensation, musty smells, and hidden mould, and creating a cleaner, more comfortable living environment.
Energytight™ Retrofit options
IECC data shows that airtightness has the greatest impact on home energy efficiency, yet until recently, it was difficult to achieve in existing homes. With the introduction of AeroBarrier by Aero, practical airtightness upgrades are now possible in New Zealand, unlocking two key pathways:
- Deep Renovation: For major renovations, adding airtightness can capture the missing 40% of energy savings often left on the table.
- Energytight™ Retrofit: As a stand-alone upgrade, airtightness combined with mechanical ventilation can deliver energy performance equal to—or even better than—traditional wall insulation retrofits, without the high cost and disruption.
Traditional Renovation
(Wall insulation, not airtightness)
Potential Energy Use Reduction 61%
Energytight™ Retrofit
(Airtightness ans windows, not insulation)
Potential Energy Use Reduction 67%
Deep Renovation
(Traditional renovation plus Airtightness)
Potential Energy Use Reduction 100%
| Process | Traditional Renovation | Energytight™ Retrofit |
|---|---|---|
| Add ceiling and floor insulation |  |  |
| Remove wall linings |  | |
| Remove skirting and architrave |  | |
| Create wall cavity |  | |
| Install wall insulation |  | |
| Fix and stop new wall linings |  | |
| Fix skirting and architrave |  | |
| Remove windows |  | |
| Fit new frames and windows |  | |
| Retrofit new glazing in existing frames | |  |
| Airseal house | |  |
| Install ventilation system | |  |
| Potential impact on energy saving - based on IECC data. | 61% | 74% |
Energytight™ Retrofit
Retrofitting wall insulation in an existing home is often disruptive, expensive, and time-consuming—typically requiring the removal of wall linings, skirtings, and architraves, followed by reconstruction. In contrast, improving airtightness offers a much faster, more affordable solution. Using AeroBarrier, the building envelope can be sealed in just a few days with far less disruption than traditional renovation. While the process can be completed in occupied homes with some additional preparation, it is most efficient when the home is unoccupied—such as between owners, tenants, or during renovations.
Backed by IECC data, this approach can achieve greater energy savings than traditional insulation upgrades alone. And the benefits go beyond efficiency: enhanced airtightness also improves indoor air quality, reduces moisture-related issues, and extends the life of the building.
Renovations
When renovating, the goal is often to create a beautiful, comfortable home, but without addressing insulation or airtightness, performance can fall short. A home may look brand new, yet remain cold, damp, and difficult to heat.
For the best energy efficiency, a full “Deep Renovation” that includes both insulation and airtightness is ideal. However, simply incorporating airtightness into your renovation plan can deliver comparable energy performance to traditional methods—at significantly lower cost and with far less disruption.
AeroBarrier Airsealing: A Simple Solution for Airtightness
Achieving energy efficiency in existing homes was once complex and costly. AeroBarrier changes that by systematically sealing air leaks boosting energy efficiency without the need to remove wall linings or add insulation.
A well-established technology and process
- Over 200,000 homes sealed annually in North America and Europe
- Now available in New Zealand, offering a simple, cost effective retrofit solution
“Once the basic joinery is taken care of, this technology allows the guys to dial in whatever level of airtightness they want, then confirm that they’ve met it. It’s that easy”
MATTHEW CUTLER-WELSH, NZ GREEN BUILDING COUNCIL
The Energytight™ System: Proven Performance, Certified Results
- Energy Efficiency – Significantly reduced energy use
- Comfort – Stable indoor temperatures year-round
- Health – Clean, filtered air with no hidden mould
- Durability – Moisture control that protects the structure
All backed by verified airtightness testing—real results, not just promises.
One Tree Hill: A Deep Renovation Case Study
The One Tree Hill College Trade Academy project demonstrates the impact of airtightness in a typical 1970s Kāinga Ora home.Using AeroBarrier, the project reduced air leakage from 19 ACH50 to just 1.7 ACH50, achieving Homestar 7 certification.
- Initial Airtightness: 19 ACH50
- Final Result: 1.7 ACH50
- Outcome: An Energy efficient, healthy, affordable home
“We’ve taken a 1970s Kāinga Ora home from 19 air changes down to just 1.7 ACH50—a level of performance well beyond most new builds. Absolutely amazing.”
CHARLOTTE MCKEON, PROJECT LEADER, ONE TREE HILL TRADE ACADEMY
Conclusion
Airtightness provides one of the most effective, affordable ways to upgrade New Zealand’s aging homes—without the cost and disruption of conventional renovations. The Energytight™ Retrofit solution combines air sealing and mechanical ventilation to deliver healthier, more comfortable, and dramatically more energy-efficient homes. It’s a simple path to high performance—backed by data, proven in the field, and ready for scale.
