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Aero Study Report

Typical airtightness of New Homes in New Zealand. AeroBarrier Case Study

Background

This report summarises airtightness results from new-build homes completed last year. It provides a practical snapshot of how new homes in New Zealand are typically performing.

The sample mainly includes Homestar projects and builders aiming to deliver above-Code homes. As a result, these builders are generally more aware of airtightness and trying to achieve better outcomes. The pre-airsealing results in this report are therefore likely to be better than the wider industry average.

Renovations, retrofits, SIP construction, and Passive House projects are excluded to focus on typical new-build construction.

Highlights

New Zealand new-build homes in the sample averaged around 6–7 ACH50 airtightness after adjustment, showing that most production housing still allows a relatively high level of air leakage.
Even homes designed to higher standards such as Homestar projects showed wide variation in performance, ranging from about 4.21 to 10.72 ACH50.
The results closely align with international research from Australia, where typical new homes measure around 7–9 ACH50, suggesting similar construction outcomes across both markets.
The study shows that airtightness is highly dependent on build quality and envelope detailing, with large performance differences even within the same builder category.

Sample Overview

Type of Project	Sample Size	Avg Before Sealing (Masked)	Avg Before Sealing (Adjusted)	Highest (Adjusted)	Lowest (Adjusted)
	Number	ACH50	ACH50	ACH50	ACH50
Homestar	37	5.46	6.46	10.72	4.21
New Build	6	6.15	7.15	9.17	5.42

Masked

Envelope-only airtightness test with operational components sealed (rangehoods, ducts, hatches, doors, windows).

Adjusted: Masked result + 1 ACH50 to reflect expected operational leakage once systems are unsealed and functioning. This allowance is based on post airsealing blower door testing data.

Masked vs Adjusted Results and Operational Leakage

Airtightness results are reported in two forms:

Masked (envelope-only): Operational components such as rangehoods, ducts, hatches, doors, and windows are sealed to measure the airtightness of the building envelope alone (walls, roof, floor, and fixed junctions).
Adjusted (indicative operational): An allowance is added to reflect expected in-service airflow from components designed to open, move, or ventilate.

Operational leakage represents normal airflow from items such as:

Rangehood and bathroom exhaust dampers
Ducts and flues
Attic hatches
Sliders and window seals

This leakage is not a defect; it reflects the building operating as intended. Airtightness systems (e.g., SIP panels, intelligent membranes, AeroBarrier) are designed to improve the envelope but are not intended to eliminate operational airflow.

Based on testing of masked and unmasked homes, a practical allowance of +1.0 ACH50 has been applied to the table above to provide a reasonable operational figure. An indicative range of +0.5 to +1.5 ACH50 is appropriate, depending on dwelling type, number of service penetrations, and the quality of operational components and their installation.

Insights from the Data

1. Homestar projects are tighter on average—but still variable

Average adjusted result: 6.46 ACH50
Range: 4.21 to 10.72 ACH50

Even among projects targeting higher performance, airtightness varied significantly.

Insight: Design intent alone does not guarantee airtightness. Execution quality and envelope detailing remain critical.

2. Standard new builds remain relatively leaky

Based on the Aero empirical data.

Average adjusted airtightness of homes air sealed: 7.15 ACH50
Range: 5.42 to 9.17 ACH50

These results closely align with international findings.

CSIRO / ATTMA Research (Australia)

Average new home: 8 ACH50

Single storey: 7 ACH50
Two storey: 9 ACH50

Insight: New Zealand production housing appears consistent with Australian data. While performance has improved over the past decade, average airtightness remains well above high-performance benchmarks.

One of the house builders, operating at a higher specification level, recorded the lowest adjusted result among standard builders at 5.42 ACH50, indicating their higher specification and focus on quality, performance outcomes. Despite that, they were still over 5 ACH50 adjusted.

3. Variation within builder categories is significant

Homestar projects varied by 6.5 ACH50 between best and worst.
Standard builds varied by nearly 4 ACH50 between best and worst.

Insight: Airtightness is one of the most variable aspects of construction quality. Without deliberate envelope control, results are inconsistent and unpredictable.

Overall Observations

Average production housing in this sample sits between 6–7 ACH50 (adjusted).
Results align closely with CSIRO and ATTMA international data.
Homestar-targeted homes perform somewhat better but still exhibit wide variation.
The spread between best and worst homes remains substantial within each category.
Airtightness in mainstream construction remains largely unmanaged rather than systematically controlled.
The ECCHO assumption that a “typical” new home starts at 5 ACH50 does not reflect this dataset. Actual averages are materially higher, indicating that the potential value of improving airtightness may be understated.

Conclusion

The data indicates that:

Airtightness performance in new builds remains highly variable.
Higher design standards alone do not ensure consistently low leakage.
Envelope detailing and build quality are the primary determinants of performance.
New Zealand industry averages are broadly consistent with Australian findings (~8 ACH50), though better outcomes are achievable with higher specifications and deliberate control.

This dataset highlights a clear opportunity for more systematic airtightness management to improve consistency and reduce overall leakage in new housing.