The research is clear:
Airtightness drives energy efficiency more than any other factor.
It all starts with airtightness
Airtightness is the leading factor in achieving energy efficiency in home design, construction, and renovation.
In countries like the USA, UK, and across Europe, minimum airtightness levels are mandated by building codes to meet energy performance targets.
That’s because airtightness is widely recognised in building science as one of the most effective ways to reduce energy loss.
Globally respected standards, such as IECC and ENERGY STAR reinforce this. At the ANSI/RESNET Conference (November 2023), airtightness was ranked as the single most important factor in residential energy performance.
Measuring Airtightness – The First Step to Energy Efficiency
Airtightness is measured using ACH50 (Air Changes per Hour at 50 Pascals), which indicates how often a home’s air is replaced through leaks under test pressure. Lower ACH50 values mean a more airtight, energy-efficient building envelope.
Although well understood by building scientists, New Zealand’s building code still does not require airtightness testing—leaving it up to builders and homeowners to go beyond the minimum. BRANZ recommends a target of 3 ACH50 or better for homes aiming to chieve
good energy performance.
Airtightness and ventilation – a perfect partnership
Your home needs to breathe, and it needs to breathe all the time – just like you. Just as you would not survive breathing now and then, opening doors and windows every now and then is not a realistic solution. With proper controlled ventilation delivered by mechanical ventilation systems means clean, healthy air all the time, while minimising heat and energy losses.
A mechanical ventilation system controls the airflow in an airtight home. If that ventilation system features heat recovery, energy loss is minimised, creating a highly energy-efficient home.
BRANZ research shows that combining a high-performance heat recovery ventilation system with a very airtight home (1 ACH50) can deliver energy efficiency gains of up to 90 per cent!
BRANZ study:
The Impact of Airtightness on Energy Efficiency
BRANZ scientists upgraded an old house to meet current code standards, then gradually improved its airtightness while maintaining a constant indoor temperature of 20°C. They measured the actual energy used for heating and found that reducing airtightness from 9 ACH50 to 1 ACH50 delivered approximately 50% energy savings. Adding high-performance heat recovery ventilation (MVHR) provided a further 40% improvement—resulting in a total energy saving of around 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.
Key findings:
- Airtightness alone: Increasing airtightness from 9 ACH50 to 1 ACH50 reduced energy use by around 50%.
- MVHR: Adding heat recovery ventilation further increased energy savings by up to 40%
- Combined airtightness and MVHR: energy improvement of up to 90%.
Dwelling type
Single storey house
Two storey house
Average
Average ACH50
Maximum ACH50
New Homes Average 8 ACH50 – A Big Opportunity for Improved Efficiency
A recent study, Air Infiltration of New Dwellings in Australia (Michael Ambrose & Sean Maxwell, June 2024), tested 233 newly built homes in major cities including Melbourne, Sydney, Brisbane, Canberra, and Adelaide.
All homes were typical constructions with no specific airtightness strategies in place. Testing was conducted using ATTMA Technical Standard L1 (TSL1).
The average airtightness of new houses was found to be 8 ACH50.
These results closely match observations from Aero’s blower door tests in New Zealand, confirming that most new homes are not built airtight by default.
Unlocking Hidden Efficiency: How Airtightness and Ventilation Transform New Homes
“Build tight, ventilate right”: why both are essential
The phrase “Build tight, ventilate right” is a guiding principle in high-performance home design. The idea is simple: first, make the building envelope as airtight as possible to eliminate unwanted heat loss and air leakage. Then, introduce controlled, mechanical ventilation to provide a steady supply of fresh, healthy air and effective moisture control.
Without airtight construction:
- Heat escapes through gaps and cracks, raising energy bills and reducing comfort.
- Mechanical ventilation systems (especially MVHR) can’t operate efficiently.
- Indoor air quality suffers, increasing the risk of condensation, mould, and poor health.
Airtightness and ventilation aren’t in conflict—they’re complementary. Together, they create homes that are energy-efficient, healthy, and comfortable to live in. Modern MVHR systems are low-energy and work best in airtight homes.
You Can Feel the Difference with the Energytight™ Solution
Fresh air. No draughts. No condensation. Just a quieter, more comfortable home that feels better every day.
The Energytight™ Solution achieves certified airtightness of 3 ACH50 or better, combined with mechanical ventilation with heat recovery (MVHR). Backed by BRANZ, CSIRO, and international best practice, it delivers warmer, drier, healthier, and more energy-efficient homes.
With airtightness likely to become part of building code soon, designing for it now helps future-proof your home and avoid early obsolescence.
If we want homes that are truly fit for the future—comfortable, healthy, and efficient—airtightness and ventilation must be part of the design from the start.
Want to experience the difference? Email us to arrange a visit to a nearby show home.
To learn how to apply the Energytight™ Solution, book a free online or in-person CPD session today.
References: Impact of airtightness and ventilation on energy efficiency BRANZ and SIMX
What Is the Energytight™ Solution?
Energytight™ is the new standard by Aero that defines the benchmark in energy-efficient, high-performance homes. Powered by AeroBarrier®, the Energytight™ solution seals invisible air leaks, delivering precise, measurable airtightness.
Our CPD presentation explains how airtightness supports building performance. It includes technical and background information and case studies any New Zealand residential architect will find useful.
