Some builders are concerned about making home too airtight Some arguments they give are:

1. “Humans need to breathe, and so does a building.”
2. “We don’t want occupants suffocating—fresh air has to come from somewhere.”
3. “If the building is too tight, we’ll need to install an HRV or ERV system.”
4. “If we’re relying on natural ventilation, why worry about air leakage?”
5. “We don’t want mould growing in our buildings.”

To begin with, these concerns stem from of lack of ventilation, not airtightness.  Air leakage is NOT ventilation. So lets get back to basics:

What is Ventilation?

Ventilation is the intentional introduction of outdoor air into a building, either through natural or mechanical means. In apartments or enclosed buildings, it’s also crucial to consult with a fire engineer and implement a pressure relief strategy for fire safety.

• Natural ventilation relies on open windows, vents, and other planned openings, driven by wind and temperature differences.

• Mechanical ventilation uses fans to deliberately supply or exhaust air.

For ventilation to be effective we need to consider the quantity, the quality, and the distribution of air into an occupied space. Can air leakage satisfy these three factors? Here’s why it falls short:

• Air from leaks is not filtered. It may come from a mouldy, dusty, or vermin-infested building cavity.
• There is no way to easily temper the air coming in, so it brings the temperature, humidity or dryness of the outside with it.
• Air leakage leaves you at the mercy of the weather. On windy, hot, or cold days, there is lots of air exchange. But on calm days there is almost none.
• Because you can’t locate or control all air leaks, it’s very hard to make sure each room gets the right amount of fresh air.

There is no way to compare air leakage with ventilation! Not only does infiltration fail to meet ventilation needs, but it also has additional harmful effects to your building and the health of its occupants.

Condensation and Mould Risk

When infiltration brings air from outside, it can create localised cold spots in walls, floors, and ceilings. These have the potential to create condensation, which can lead to mould growth or stains on finishes. Unchecked, condensation can lead to rotting or corrosion of materials, causing structural damage. It also makes a more inviting habitat for a termite infestation. Mould hidden inside walls can spread spores throughout the home and is nearly impossible to clean.

For buildings that are designed for natural ventilation, the openings should be fitted with condensate drains and be constructed using water-resistant materials. The location of these openings should be accessible for cleaning and maintenance. The most common example is mould that forms on leaky windows, which can be cleaned easily.

Reduced Insulation Performance

When insulation materials are rated in the laboratory, they are under controlled conditions with no air moving through the test sample. In the real world, air leaks can pass air through insulation, which substantially reduces insulation performance in two ways:

• Direct bypass – air leakage can pass right around both rigid and fibrous insulation
• Wind washing – air can pass through bulk insulation material itself, disturbing air pockets trapped by the fibres and stealing the heat it is meant to retain

Unwanted distribution of pollutants throughout the building

In leaky buildings, pollutants can distribute through a building via unintentional gaps and cracks. This can create problems ranging from minor nuisances such as odours to more serious issues such as carbon monoxide from a garage or car park. Most dangerously, they are a potential path of smoke in the case of a fire.

Other issues from air leakage

Air leakage in larger buildings can also contribute to noise infiltration and noise production from whistling under windy conditions. Lastly, any hole to the outside, garage, underground car parks or other unconditioned spaces serve as easy paths pollutants or unwanted pests. Sealing up these paths is the cheapest and first method of pest control.

To address concerns for airtightness in homes:

When someone says a house “needs to breathe,” ask them to breathe through their eyes. Sounds ridiculous, right? Humans breathe through their mouth or nose—designed for that purpose. Homes should do the same: breathe through designed ventilation systems.

Key points:

• You can’t make a home too airtight if you provide proper ventilation.

• For typical homes, mechanical ventilation can be simple and low-cost. A continuously running, remote-mounted exhaust fan is quiet and energy-efficient.

• Air should never come through walls—true fresh air should be filtered, controlled, and delivered where needed.

• To prevent mould and condensation, combine mechanical ventilation with thermal bridge control. Even uninsulated outdoor areas like carport soffits can grow mould, showing that moisture control is more complex than ventilation alone.

Why Air Barrier Integrity Auditing Matters

Air barrier integrity auditing is essential for ensuring that airtightness targets are met efficiently. The key benefits of this process include:

• Precisely locating air leakage issues.
• Verifying the correct air barrier materials are being used for long-term performance.
• Providing timely reports, allowing remediation before finishes are applied.
• Capturing photographic evidence of remediation work.
• Identifying discontinuities in the air barrier at building junctions and façades using ultrasonic technology.
• Recommending compliant remediation solutions in line with the Australian Building Code.

If a QA process is not conducted regularly at key intervals during construction, airtightness targets can become a very expensive exercise. Remediation works that happen after construction can have the potential to not last the test of time. Or they may not even be possible due to safety.

Location, Location, Location

Commercial Buildings can be large and complicated, so it is important that plans are marked up with problematic details. If trades cannot find issues, they just won’t fix them.  If issues cannot be relocated to verify remediation, then the whole process of air barrier integrity auditing is rendered ineffective and pointless.

Verification of building materials

In some circumstances, building materials specified for the air barrier may be inadvertently costed out, or supplied with an inappropriate product.  Certain tapes or sealants may not be compatible together or may react undesirably when exposed to environments during construction.  It’s important to catch these issues during construction so that they can be repaired in a timely manner before finishes.

Report turnover

Projects can move extremely fast, and it is not uncommon for the fit-out to begin before service risers are complete.  Once an inspection is conducted, a report must be issued with all the location details marked off an up-to-date floor plan. Additionally, it should include recommended fixes and dimensions of the issue, with the direction of how the air barrier should be continued.

Photo evidence

Photos of issues should be marked up to clearly articulate to trades the whole that must be closed in.  Airtightness is not always obvious.

Troubleshooting during construction

Troubleshooting and confirming air leakage through the air barrier when the building is under construction is difficult.  There are technologies available to help confirm non-obvious gaps in building elements.  Ultrasonic sound auditing can add significant value.An array of ultrasonic transmitters which generate ultrasonic waves are set up on the outside.  This makes it possible to find gaps in curtain wall facades, leaks through building elements, door frames/window frames and window/door seals, even ducts and plenums.

The ultrasonic detector picks up ultrasound via a microphone and converts the inaudible ultrasound into an audible frequency and in some circumstances overlays the frequency emission location on top of a visual image with a representative highlighted colour.  A visual representation is bundled together using a directional array of receivers capable of picking up ultrasonic sound waves while suppressing other noise and outputting onto an image. When auditing ultrasonic sound gets louder the closer you get to the leak and is quickly muffled as it moves through the air.  The ultrasonic leak detection can pinpoint even the smallest leaks in a partly constructed building, which is the most economic time to organise a solution.

Recommended Remediation

During construction, drawings sometimes miss air barrier continuity.  Different materials that make up the air barrier have different surfaces. Therefore, different products need to be used depending on the circumstances to ensure the longevity of the air barrier over the building’s lifetime.

Air barrier integrity auditing is a critical part of building commissioning. An engaged airtightness coordinator coupled with good building design and detailing, makes airtightness targets like PassiveHouse achievable and economical.

Not all wall wraps are created equal. Different users have different requirements and expectations for what they want their wrap to do.
In most cases we should, and can expect modern nonwoven textile wraps to control:

1. Water – Prevent rainwater from entering the building during construction before cladding is installed. This protects insulation, internal services, and finishes that aren’t designed for exposure, reducing risks to both occupant health and structural integrity.
2. Air – After construction, uncontrolled air movement can worsen moisture problems, enable water ingress, introduce unwanted noise, increase heat loss/gain, and allow the spread of fire and smoke.
3. Water Vapour – Condensation and high humidity can cause mould, rot, and long-term damage to structural elements.
4. Fire Safety – Wraps should not contribute significantly to combustibility in the building envelope. Some glass/aluminium laminates are classified as non-combustible under the NCC, while vapour-permeable and foil laminate wraps are generally of low flammability, not non-combustible.

Sometimes we may be forced to compromise on some of these control layers, but we also need to pay attention to the minimum requirements in the National Construction Code (NCC).

NCC 2019: Improved Clarity for Combustibility Compliance

The 2019 update to the NCC clarified which materials can be used in areas requiring non-combustible construction. Key excerpts from Clause C1.9 include:

• (a) In Type A or B buildings, external walls (including all components like facade, framing, and insulation), lift pit floors, and certain internal fire-rated walls must be non-combustible.

• (b) Non-loadbearing shafts must be non-combustible if they span more than two storeys in relevant building classes.

• (c) A loadbearing internal wall and a loadbearing fire wall, including those that are part of a loadbearing shaft, must
  comply with Specification C1.1.

• (d) Exemptions include gaskets, caulking, sealants, termite barriers, laminated glass, glazing thermal breaks, and damp-proof courses.

• (e) Permitted materials where non-combustibility is required include plasterboard, fibre-cement sheeting, bonded laminated materials (if each layer is non-combustible and adhesives are thin), and sarking-type materials ≤1mm thick with a Flammability Index ≤5.

The NCC 2019 update resolved long-standing conflicts where non-combustibility requirements clashed with the need for air, water, and vapour control—especially in external wall assemblies.

The Challenge of Wrap Performance: Vapour vs Airtightness

There never has been a wrap product available that meets the NCC requirement for non-combustibility, while at the same time as being an effective air and water barrier, combined with sufficient vapour permeability for use in cool and temperate climates.

Current products on the market today that are deemed non-combustible are made from pure aluminium foil laminated, an adhesive layer and a woven glass cloth.  Aluminium Foil when reinforced can be very airtight, but these products are also extremely vapor tight (Incapable of allowing moisture vapour to escape/permeate to the outside).

To improve vapour permeability, some manufacturers perforate the foil—creating a trade-off. These perforations compromise water and air barrier performance. After all, nobody sells umbrellas with holes in them.

On the other side of the equation, with aluminium foil type wraps, if the holes are so small and infrequent, these types of products still struggle as a vapour permeable underlay. Like single glazed glass windows, aluminium foil is a non-porous material, and it is prone to condensation forming on its surface. Over the past year, some manufacturers have published questionable vapour permeance values, with figures shifting from plausible to implausible and back again.

Polyolefin Textiles: A Better Option

Well established polyolefin textile air and watertight vapour permeable wraps can provide a far superior vapour permeability performance without compromising other important features.

If following a deemed to satisfy path using NCC 2016, it will require some compromise of water tightness, air tightness or vapour permeability.  The only realistic option to date has been to insulate externally the non-combustible sarking, use a non-combustible vapour permeable sheathing board, or follow a performance solution / fire engineered pathway.

Water Barrier Classification: AS 4200.1

Looking at the requirements of a water barrier under the AS4200.1: 1994 code for sarking you can see that almost all perforated aluminium-based materials are unhelpfully classified as:

“Water Barrier – Unclassified”

6.4 Water barrier – The water barrier classification shall be neither high nor unclassified. The resistance to water penetration shall be determined, as required, by the method described in AS/NZS 4201.4. as follows:

(a) High The material shall only be classified as high if it passes the test,

(b) Unclassified When the material is not classified as high, it shall be unclassified.

In terms of AS4200.1 : 1994 classification, if a datasheet is reporting a product to be “unclassified”, it means it has not passed the water barrier test which is a simple 10cm standing head of water test.

The current version of AS4200.1: 2018 is more helpful to the user and the product will now be defined as:

“Water Barrier – Non-water barrier”

5.3.5 Water control classification

The water control classifications shall be determined as follows;

(a) Water barrier – if the membrane passes the test specified as AS/NZS4201.4.

(b) Non-water barrier – if the membrane fails the test specified in or has not been tested to AS/NZS 4201.4.

How then have things changed for classification of vapor permeance?

Vapour Control Requirements

In the 1994 version of the code there was no classification of vapour permeance. Products were either a low, medium or high classification as a vapour barrier.  Just because a material wasn’t a particularly fantastic vapour barrier does not imply that it is sufficiently vapour permeable.

The 2019 NCC Condensation Management DTS requirements for climate zones 6,7 & 8 now requires a vapour permeable membrane, In the updated 2017 version of A4200.1 vapour barrier and vapour permeable membranes using table 4.  See below.  (Southern Australia and Alpine areas)

We should only be seriously using class 4 products with a vapour permeance of >1.14µg/N.s  Class 3 seems like a bit of a holdover from the old building code to cover the old “perforated” foil wraps Perforated sarking).

When considering that a typical paper faced plasterboard has a permeance of around 2.0µg/N.s  then it is a good rule of thumb to ensure the external wrap is at least as permeable (>2.0µg/N.s) as the interior plasterboard lining. In order to control moisture successfully inside a wall system the vapour permeability of materials is increasingly vapour permeable toward the outside of the wall system.

TABLE 4

VAPOUR CONTROL MEMBRANE (VCM) CLASSIFICATION

Vapour permeance (see Note)

Class	VCM Category	Min. (μg/N.s)	Max. (μg/N.s)
Class 1	Vapour Barrier	0.0000	0.0022
Class 2		0.0022	0.1429
Class 3	Vapour Permeable	0.1429	1.1403
Class 4		1.1403	No max.
	ASTM-E96 Method B Wet Cup - 28 C 50%RH

NOTE: Vapour permeance is the inverse of vapour resistance. It shall be calculated as follows:

Vapour permeance μg/N.s = 1/(Vapour resistance MN.s/g)

Almost all building wraps are technically combustible, but the caloric value (the heat produced by the complete combustion) of wraps is quite small compared to the volume of materials that are non-combustible in a wall system.

According to NCC2019 building wraps/membranes that are less than 1mm thickness with a flammability index of no greater than 5 can be used wherever a non-combustible material is required.  This means you can now have your cake and eat it.  For applications using NCC 2016, in most cases, your only solution is to discuss with your fire engineer about a performance solution.

Using Vapour Permeable Wraps at the Bottom of wall detailed with air tightness.

Getting an airtight barrier at the bottom of a brick veneer wall system using damp-course as your air barrier, with an overlap from a vapour permeable wrap. If you have any questions, please contact us.

Why targeting ACH is not quite right

Using Air Changes per Hour (ACH) at 50Pa or even at ambient pressures like 4Pa — which are volume-based measurements — rather than a permeability rate (which is surface area-based) misrepresents how leaky a commercial or industrial facility really is. When ACH is used as the metric, larger enclosures will appear to perform better simply due to their size — not necessarily because of better build quality. This means that a consistent standard leakage rate cannot be reliably specified when ACH is the target.  Compare the ACH for these 3 examples.

A standard single-storey house

Floor Area: 125m2

Volume: 300m3

Surface area: 389.5m2

A building at 5 m3/h/m2@50Pa would be 6.5ACH@50Pa

OR

A standard single-storey Passive house

Floor Area: 125m2

Volume: 300m3

Surface area: 389.5m2

A building that achieves passive house .6ACH@50Pa needs to achieve .462 m3/h/m2@50Pa 

Smaller volumes or components of buildings trying to achieve .6ACH@50Pa can be next to IMPOSSIBLE to achieve when services penetrations and windows are a part of the building fabric.

Not much of a problem for now, the permeability rate and air change rate are very similar, due to these types of buildings usually being quite small. Volume and Surface area numbers are largely similar.  (However, very large homes, can enjoy the benefits of ACH)

Small Commercial BuildingVolume: 20m x 20m x 12m = 4800m3

Surface area: 1760m2

A building at 5 m3/h/m2@50Pa would be 1.83 ACH@50Pa

Identical Build quality as the home but it enjoys over THREE times lower ACH Rate

Large Commercial Building

20m x 20m x 260m = 104,000m3

Surface area: 21600m

A building at 5 m3/h/m2@50Pa would be 1.03ACH@50Pa

Identical Build quality as the home but it enjoys a FIVE times lower ACH Rate.  This building could be Passive house air tight if passive house didn’t have the rule that buildings larger than 4000m3 in volume need to use a permeability rate.

Using ACH on Commercial buildings, Oil & Gas rig refuges or any type of large enclosure larger than 3000m3 in volume, means the larger the enclosure, the easier it is to pass a particular target inadvertently.  For build quality, a permeability rate which uses the surface area of the building, requires a target based on air flow through a square meter of building envelope with simulated airspeeds of 32km/h winds.  This standard methodology ensures results are meaningful, reproducible, and comparable across buildings of all sizes.

Find out more about the Building Code of Australia and its guidelines here.

Achieving an Air Permeability Rate Requires Seeing the Unseen

Energy efficiency hinges on controlling heat and air flows, which begins with containing air. Designing an energy-efficient building involves specifying an air barrier in plans, selecting appropriate sealing products, and ensuring correct installation during construction. Ultimately, a blower door test validates the effectiveness of these efforts. However, since air is invisible, untrained eyes don’t know what to look for.

The Blower Door Test: A Crucial Tool

A blower door test is an essential tool for energy-efficient builders. It uses fans to induce a pressure on the building envelope and pressure gauges to measure how well the building can hold that pressure. Since it can be done on almost any building, it provides to compare the airtightness of one building to another. Many areas in the U.S. and Europe require them in their building codes. In this country, the Green Building Council of Australia’s Green Star rating system offers an Innovation Challenge point for doing the test and another for achieving best practice air permeability.

Despite its usefulness, blower door testing is underutilized in Australia, particularly in Sydney, where a scarcity of experienced practitioners risks tests being awarded solely based on lowest cost. Critically, blower door testing itself does not save energy. Just like other diagnostic tools, it merely is a way to check envelope performance at a particular stage of construction. Many builders, either unfamiliar with the test or overly confident that they know what they’re doing, go about their regular business and call for the test at the end. But if testing at the end is all you do, the builder is largely aiming for a target he cannot see.

Within seconds of turning on the blower door fans, an experienced tester can tell how well the builder has been made airtight. If they have done an excellent job, everyone breathes a sigh of relief and pats each other on the back. If they fail, the next step can lead to finger-pointing. The owner blames the architect, who blames the contractor, who blames the worker, who turns around and blames the project team because he wasn’t given adequate instruction. In truth, all are responsible. Fixing the problems at the end of construction can be especially expensive because solutions often lie beneath the surface. This is not a situation that anyone wants.

The real usefulness of a blower door lies in its ability to help you see the unseen, to call attention to things you may have missed. But before construction even begins, an experienced building science firm can see weak points in your plans and details before they become a reality and offer constructive advice on how to cost-effectively fix them. On-site during construction, their eyes can spot mistakes before they are repeated. A smaller-scale preliminary test early in construction can help you identify problems when it is so much cheaper to fix them. Variations on the test can help you uncover the causes and determine solutions so that these can be replicated on the rest of the project for maximum effect. In the case of a failure, an experienced firm knows how to fix the problems and who to call.

The best building science firms help you pass an air permeability test before they even turn the blower doors on. For these reasons, it matters quite a lot who you choose to test your building. In short, experience counts. In the hands of an experienced building science firm, the power of a blower door test is not the number you get, but the ability to help you see the unseen.

Efficiency Matrix is the only experienced, fully equipped infiltration testing firm with a permanent presence in Sydney. They possess the most combined blower door testing experience of anyone in Australia. John Konstantakopoulos’s company has the largest set of calibrated, professional-grade fans, infrared cameras, and diagnostic equipment in Australia, and he has done more large-building infiltration tests in Australia than anyone in the country. His relationship with builders over the years has earned him repeat business from multiple large and medium construction companies.

Introduction

Efficiency Matrix has over 20 years of experience in airtightness testing services and products. We are the leading airtightness testing company in Australasia. Working in many different industries throughout Australia, we are an ATTMA Level 2 certified tester, and we pride ourselves on helping clients proactively understand the benefits of build quality where airtightness and insulation consistency are concerned.

We have the largest capability in airtightness testing within Asia, with over 20 calibrated blower door fans. 17 of our fans are commercial-grade fans moving up to 14,000m3/h each.

As well as an extensive evaluation of technology and best practices from around the world, Efficiency Matrix now provides the most comprehensive, global best practice building envelope air barrier evaluation process and retrofitting capabilities in Australia. Go to our Air Tightness Consultancy page for more information.

Our Air Leakage services include:

• Green Star
• Defect reporting with intrinsically safe photographic equipment
• Facade Testing
• High-resolution Riser inspections with robotic equipment with floodlights
• Remediation works, of the building envelope
• Ultrasonic Sound testing for air tightness
• Detailed riser inspections using mining grade photographic equipment
• Automated sealing up of ductwork and floor plenums
• Building pressurisation services for Airtightness in Residential homes in Melbourne.
• Ductwork pressurisation in residential homes.
• Commercial Air tightness testing services for Green Star.  (The largest capability in Australia for testing the largest of buildings)
• Thermal imaging for insulation consistency and locating draughts in the building envelope.
• Smoke testing
• Appraisal of architectural drawings for air tightness design
• Building airtightness sealing
• Consultation on ventilation strategies in homes.
• Product recommendations for airtightness of the building envelope.
• Marketing material of energy efficient products for manufacturers of products.
• Testing airtightness of devices that penetrate the building envelope
• Floor plenum testing
• Floor plenum automated sealing
• Supply and return plenum air tightness testing
• Commercial ductwork air tightness testing
• Commercial duct sealing, for ventilation or HVAC services
• Penetration auditing and reporting, quantifying the overall size of holes.
• Tracer gas analysis
• Testing to Australian and/or international standards
• Modelling air tightness benefits in a building design, taking into consideration, stack effect and wind effects.
• Supplier of Fire rating building envelope extension products for plaster ceilings
• Supplier of door and window sealing products
• Oil and Gas / On shore mining

We provide a one-stop-shop turnkey solution to assist builders/property owners in learning about and achieving airtightness in their projects. We have a proven track record with amazing results. Contact us for our references.

Building pressurisation is extremely popular overseas in quantifying and scientifically proving some degree of airtightness for demonstrating energy efficiency in a home.

Troubleshooting

1. With thermal imaging, reporting is marked off on a plan with an estimation of the percentage of uncoverage. Up to 3MP in resolution photos, up to 1024×768 video thermal imaging.
2. Mining-grade inspection cameras for Riser and ductwork inspections.
3. Ultrasonic sound auditing
4. Theatrical smoke testing
5. Smoke stick testing
6. Guarded blower door testing
7. Flowhood airflow testing to work out how many particular items leak (R&D)

Correct ventilation in a home/building should always be by design and not by poor construction quality. Give us a call regarding your projects.

Efficiency Matrix is accredited to perform airtightness testing to:

AS/NZS ISO 9972: Thermal Performance of buildings – determination of air permeability of buildings – fan pressurisation method
BS EN 13829: Thermal Performance of buildings – determination of air permeability of buildings – fan pressurisation method

Proud members of:
AIRAH (Australian Institute of Refrigeration, Air-Conditioning and Heating)
AIVAA (Air Infiltration and Ventilation Association of Australia)
ATTMA (Air Tightness Testing & Measurement Association)

Just some of our clients