Recommended Changes to Australia’s National Construction Code to Improve Energy Efficiency Through Improved Building Envelope Air Tightness

Compiled by Sean Maxwell, Air Infiltration and Ventilation Association of Australia

8 December 2015

The National Energy Efficient Building Project, led by the South Australian government, issued a report last year identifying major impediments to achieving better energy efficiency in Australian buildings. Largely leaving aside questions about the strength or weakness of the energy efficiency provisions of the code itself, the report found that mere compliance with existing code was often viewed as lacking, and that this harms the energy efficiency goals of the code. The report concludes that “many stakeholders believe that NCC compliance is poor, implying that buildings in Australia have higher energy use, higher emissions and higher overall costs for building owners and occupants.” If the energy efficiency goals of the code and of Australia are to be realized, the code’s provisions for verification of construction quality must be strengthened.

One aspect of building quality that has a great impact on energy efficiency is air tightness. Several studies have shown that Australian homes are unfortunately built exceptionally leaky, including one commissioned by CSIRO found that the average leakage of 20 tested homes in Victoria was more than 19.7 air changes per hour at 50 Pascals. In relative terms that is close to 33 times the maximum leakage allowed for a house seeking Passive House certification, and almost four times the maximum allowed for new homes in the International Energy Conservation Code. Studies have also found a wide range of values possible, showing that some homes can be built exceptionally leaky.

Air sealing is one of the most cost-effective and durable interventions that can be made in new buildings under construction. A report by Sustainability Victoria found that even in existing buildings, air sealing can have a payback as short as 5 years. Compared to refrigerators, lighting, or other mechanical or electrical upgrades, it is also longer lasting. Many advanced nations have construction codes that give air sealing due importance, with the International Energy Conservation Code (mostly used in the U.S.) and Building Regulations in the U.K. requiring verification of airtightness through testing and/or inspection.

Testing for air tightness with a blower door, is a quick, straightforward, and repeatable measurement that requires relatively little in the way of equipment or training for verifiers. It is a very mature technology, having been a part of energy-efficient building for more than 40 years. Blower door testing can be introduced to Australian code in a way that will minimize impact on construction costs, create jobs in high-performance building, and improve comfort and energy efficiency.

The strategies outlined in this document show how it could be introduced to residential buildings, while similar strategies can be used for commercial and industrial buildings. It is not meant to be a complete set of recommendations but the start of a dialog with industry and the ABCB. The goal is to arrive at the basis of a realistic Proposal for Change to the NCC.

A Performance-Based Code Approach

One of the performance requirements of the NCC is “the sealing of the building envelope against air leakage.” There are various ways to ensure that this requirement is met, but regardless of compliance options the code should first to require that a building contain an air barrier to retard air leakage and that it is continuous and uncompromised by penetrations for services. The continuity and integrity of the air barrier must be verified.

Inspection and verification of a list of air sealing items can be viewed as a deemed-to-satisfy approach. For an unfamiliar builder, inspection is both necessary and helpful because common building practice is riddled with penetrations and discontinuities. An alternative performance-based method of compliance is a blower door test. Compliance can be relatively quickly demonstrated by conducting a blower door test on the house or apartment.

It may be a reflexive choice for some builders to go the inspection route rather than do a test. After all, a visual inspection is somewhat subjective, while a blower door test is an independently verifiable pass/fail test. Unlike a human, a blower door system cannot be convinced to reinterpret a failure as a pass. The long-term goal should be to require that all homes be tested with a blower door.

The process of introducing testing to code can be done in stages. In the graphics below, some options are shown. Starting with the 2019 code, two compliance options are available: inspections or testing to a relatively easy standard. Government can reward early adopters by either subsidizing blower door tests or by creating a label for homes that have been inspected and tested. In 2022, both inspections and blower door tests would be required. Again, government can encourage best practice by applying the label or incentives to homes that achieve an exceptional result.

This pathway gives the building industry three additional years to adapt and to learn from mistakes, before mandatory blower door testing is required in 2022. In addition, the threshold of ten air changes per hour should not be viewed as overly challenging. By comparison, the International Energy Conservation Code (IECC) requires a maximum of five air changes per hour in the mildest of climates. In subsequent years, the standard should be tightened.

Another option is to allow demonstration of compliance at different stages of construction, with different levels of stringency. For example, seven air changes per hour may be required for a blower door test done early in construction, while ten air changes per hour may be allowed at construction completion. Similar strategies are in use in the IECC for verifying heating and cooling duct tightness at different stages of construction (Section R403.3.4 “rough-in test” vs “post-construction” test).

The builder can choose to test earlier in construction when a target is harder to achieve but fixes will be easier and cheaper, or it can wait until the end of construction when the target is easier but fixes are more labor-intensive. This multiple-option approach may give builders more flexibility and indeed more opportunity to learn if they are allowed to attempt the test earlier in construction. Demonstration of greater air tightness at an earlier stage should be adequate assurance that the final goal is achieved.

Capture1 Capture2

Government and Private Industry Intervention Needed

Successful introduction of blower door testing to code would depend on several things. First, there must be an industry that is ready to implement the requirements for air sealing inspection and testing should a code requirement come into effect. Sustainability Victoria’s “Energy Efficiency in Commercial Building, Accreditation and Skills Scoping Report” identifies several industry groups that could possibly be engaged to provide these services. Efforts to develop the necessary Australian skills have also begun by forming an industry association called the Air Infiltration and Ventilation Association of Australia (AIVAA), whose members include testing professionals.

There is also a need for government intervention to aid the industry in its transition to verified construction quality. In the U.S., the ENERGY STAR for Homes label is an example of a successful government intervention. Over the past 20 years, successive versions of the program have raised the bar on what is considered energy-efficient construction, influencing code to the point that many provisions of the IECC resemble earlier elements of the voluntary program. Resources such as the ENERGY STAR’s Thermal Bypass Checklist guide aided builders in understanding the underlying building science and achieving compliance.

Similar schemes can be used in Australia to help differentiate tested and inspected homes as a value over the status quo. Looking at the marketing language, ENERGY STAR doesn’t lead with energy efficiency; they promote comfort and quality first: “The blue ENERGY STAR label on a new home means: Peace of Mind; Enduring Quality; Wall-to-Wall comfort; Proven Value.” These are all quality-related buzzwords, not energy efficiency language. By most accounts, the program has been very successful, with more than 1.6 million ENERGY STAR Homes built to date.

The Australian market may respond similarly to the U.S., and government leadership in developing and promoting a market-differentiating label for tested and inspected homes would help stimulate demand as it did in the U.S. An Australian label would denote buildings that have been inspected for proper air barrier and insulation installation, perhaps in compliance with AS 3999:2015 Bulk thermal insulation – Installation, and AS/NZS ISO 9972:2015 Thermal performance of buildings – Determination of air permeability of buildings – Fan pressurization method.



Sean Maxwell is president of the Air Infiltration and Ventilation Association of Australia, an organization of testing professionals, product suppliers, and retrofit companies concerned with improving the performance of Australian buildings through better building envelope and ductwork tightness. He recently emigrated to Australia from New York City, where he worked on ventilation and building air tightness research for the Department of Energy’s Building America program. In New York he headed a group of building scientists that successfully lobbied the State Codes Council to amend its adoption of the International Energy Conservation Code to reduce compliance costs for the construction industry and improve building quality. He is drafting similar proposals to amend the International Energy Conservation Code.

Appendix: Examples of Useful Code Language from the IECC 2012 and 2015

Outlined below is selected language from various versions of the International Energy Conservation Code and descriptions of how similar language might be applied to the Australian codes.


Blower Door Testing Year 4 Year 7 Year 7
Residential Code Requirements 2019 NCC 2022 NCC 2025 NCC
A.      Additional definitions x x x
B.      Basic requirements for air barrier x x x
C.       Specific air sealing details x x x
D.      Optional testing to 10 ACH50 x
E.       Mandatory testing to 10 ACH50 x
F.       Mandatory testing to 5-7 ACH50 x

A. Additional Definitions

  1. Define key terms relating to building tightness and energy efficiency. Some existing terms in the code can be adapted or supplemented. What is missing is a description of the concept of an air barrier whose integrity must be maintained throughout the construction process.

Sample Language from IECC

AIR BARRIER. Material(s) assembled and joined together to provide a barrier to air leakage through the building envelope. An air barrier may be a single material or a combination of materials.

BUILDING THERMAL ENVELOPE. The basement walls, exterior walls, floor, roof, and any other building elements that enclose conditioned space or provides a boundary between conditioned space and exempt or unconditioned space.

CONTINUOUS AIR BARRIER. A combination of materials and assemblies that restrict or prevent the passage of air through the building thermal envelope.

DWELLING UNIT. A single unit providing complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking and sanitation.

INFILTRATION. The uncontrolled inward air leakage into a building caused by the pressure effects of wind or the effect of differences in the indoor and outdoor air density or both.

B. Basic requirements for air barrier

  1. Expand introductory language relating to building sealing. This is necessary to establish the principle of an air barrier. It is also necessary to require that the integrity of the air barrier is maintained throughout construction.

Sample Language from IECC 2012

R402.4 Air leakage (Mandatory).

The building thermal envelope shall be constructed to limit air leakage in accordance with the requirements of Sections R402.4.1 through R402.4.4.

R402.4.1 Building thermal envelope.

The building thermal envelope shall comply with Sections R402.4.1.1 and R402.4.1.2. The sealing methods between dissimilar materials shall allow for differential expansion and contraction.

R402.4.1.1 Installation.

The components of the building thermal envelope as listed in Table R402.4.1.1 shall be installed in accordance with the manufacturer’s instructions and the criteria listed in Table R402.4.1.1, as applicable to the method of construction. Where required by the code official, an approved third party shall inspect all components and verify compliance.

C. Specific air sealing details  

  1. In the U.S., it’s up to the “code official” to verify compliance with the energy efficiency standards. It’s also up to them to determine who is “qualified” to carry out blower door testing. In some cases, this person could be the code official him/herself. The code official would normally be considered qualified to carry out the inspection. In the U.S., code officials in most states must attend mandatory trainings on updates to the code, and issues like this would be covered. In Australia, it may be possible to consider trained building certifiers or architects qualified to carry out the inspection.
  2. These details should be inspected for completion, but very likely, building certifiers currently are not trained to look for these. Enforcement would be up to states and territories. It may be possible to require inspection of details by a “qualified” professional. In the future, the term “qualified” may be more clearly defined to refer to those with specific training or certifications. A government or private industry group could use a label to differentiate those trained in air sealing inspection.
  3. List sealing details as a minimum performance requirement to be met under deemed-to-satisfy path only initially, then in subsequent versions of code in all paths. Currently the code lists a few specific details but this could be expanded considerably. Consider listing some of the following air sealing details for residential construction, adapted to Australian terminology and typical building practice.

Sample Language from IECC 2012




Air barrier and thermal barrier A continuous air barrier shall be installed in the building envelope.
Exterior thermal envelope contains a continuous air barrier.
Breaks or joints in the air barrier shall be sealed.
Air-permeable insulation shall not be used as a sealing material.
Ceiling/attic The air barrier in any dropped ceiling/soffit shall be aligned with the insulation and any gaps in the air barrier sealed.
Access openings, drop down stair or knee wall doors to unconditioned attic spaces shall be sealed.
Walls Corners and headers shall be insulated and the junction of the foundation and sill plate shall be sealed.
The junction of the top plate and top of exterior walls shall be sealed.
Exterior thermal envelope insulation for framed walls shall be installed in substantial contact and continuous alignment with the air barrier.
Knee walls shall be sealed.
Windows, skylights and doors The space between window/door jambs and framing and skylights and framing shall be sealed.
Rim joists Rim joists shall be insulated and include the air barrier.
Floors Insulation shall be installed to maintain permanent contact with underside of subfloor decking.
(including above-garage and cantilevered floors) The air barrier shall be installed at any exposed edge of insulation.
Crawl space walls Where provided in lieu of floor insulation, insulation shall be permanently attached to the crawlspace walls.
Exposed earth in unvented crawl spaces shall be covered with a Class I vapor retarder with overlapping joints taped.
Shafts, penetrations Duct shafts, utility penetrations, and flue shafts opening to exterior or unconditioned space shall be sealed.
Narrow cavities Batts in narrow cavities shall be cut to fit, or narrow cavities shall be filled by insulation that on installation readily conforms to the available cavity space.
Garage separation Air sealing shall be provided between the garage and conditioned spaces.
Recessed lighting Recessed light fixtures installed in the building thermal envelope shall be air tight, IC rated, and sealed to the drywall.
Plumbing and wiring Batt insulation shall be cut neatly to fit around wiring and plumbing in exterior walls, or insulation that on installation readily conforms to available space shall extend behind piping and wiring.
Shower/tub on exterior wall Exterior walls adjacent to showers and tubs shall be insulated and the air barrier installed separating them from the showers and tubs.
Electrical/phone box on exterior walls The air barrier shall be installed behind electrical or communication boxes or air sealed boxes shall be installed.
HVAC register boots HVAC register boots that penetrate building thermal envelope shall be sealed to the subfloor or drywall.

 C. Optional testing without targets  

  1. The question of who is qualified to carry out the test is important. In Australia, there are private, public, and non-profit bodies that offer certification for blower door testing expertise. Examples include:
  2. Use language referring to the newly-created Australian Standard AS-NZS ISO 9972-2015 for air-tightness testing, and define a relatively easy target for compliance, such as 10 ACH50. In the U.S., this threshold would be considered lax, but Australia is not prepared for a tighter standard without a significant investment in training in such a short period of time.
  3. As an alternative to inspection of air sealing details, a blower door test may be conducted to verify air sealing. The incentive to use the blower door test is that builders wouldn’t have to pay for an inspection and a blower door test. It would also be clear that during the next code cycle, blower door testing would be mandatory, so it might make sense to get used to doing the tests.
  • equipment manufacturers such as Retrotec, Infiltec, and The Energy Conservatory. Retrotec has a “Level I,” “Level II,” “Level III” designation, for example. Training bodies for this already exist in Australia and there are Retrotec-certified professionals already in Australia.
  • National Environmental Balancing Bureau (NEBB) is a U.S.-based international non-profit that certifies professionals with a Building Enclosure Testing designation. NEBB Australia is relatively new and would have to establish more trainings in this country as currently most of them are held in the U.S.
  • TAFE has offered training for blower door testing

A standardized training program would need to be created that all these bodies agree to adhere to, containing the same minimum information and training objectives. The Air Infiltration and Ventilation Association of Australia could help vet each of these programs and provide recommendations for minimum qualifications. Ultimately, it would be up to states and territories to determine who is qualified to conduct testing.

It should be possible to make the division between residential and commercial based on building Class and size. Class 1 buildings would be tested as described in this section. Class 2-9 buildings can be tested by professionals described in this section if they are relatively small. The reason for this is that small buildings can often be tested by a single technician with simple methodology.

Class 2-9 buildings over a certain size should be tested by professionals with a more substantial accreditation. Again, the above-listed bodies may be ready outlets to dispense this training, but AIVAA could gather consensus to develop a common core curriculum. Commercial standards would be similarly written to residential standards, but certification requirements for commercial building testers would need to be stronger because the tests are much more complicated. These require more experience, a more complicated methodology, and more equipment.

Testing language for Class 1 multi-residential buildings would need to be written so that the additional cost burden on builders would be minimized. We suggest a model such as that planned for adoption by New York State in the U.S., which allows systematic sampling of apartments in multi-residential buildings. This lowers cost and allows technicians with more basic qualifications to carry out testing. It also has an additional benefit of verifying apartment compartmentalization, which has benefits to occupants in the form of improved fire safety, reduced pollutant transfer, lower sound transmission, and reduced pest travel between units.

The language below, adapted from that of IECC 2015, has a different standard for single-family and multi-residential buildings. The reasons are political, mainly. This language refers to climate zones in New York State. Some of the metrics need to be converted to SI units. The test method was chosen specifically to minimize the cost of compliance to builders.

Sample Modified Language from IECC 2015 (Proposed) for New York State

R402.4.1.2 Testing.  Each dwelling unit shall be tested and verified for air leakage with a blower door at a pressure of 0.2 inches w.g. (50 Pascals) and in accordance with ASTM E779 or ASTM E 1827. Where required by the code official, testing shall be conducted by an approved third party. A written report of the results of the test shall be signed by the party conducting the test and provided to the code official. Testing shall be performed at any time after creation of all penetrations of the building thermal envelope

For detached one- and two-family dwellings, not more than three stories above grade in height, dwelling units shall be tested and verified as having an air leakage rate not exceeding 3 air changes per hour in Climate Zones 4 through 6.

For other Residential groups (R2, R3, R4) or townhouses, dwelling units shall be tested and verified as having an air leakage rate not exceeding 0.3 CFM per square foot of dwelling unit envelope area (i.e., the sum of the area of walls between dwelling units, exterior walls, ceiling, and floor) in Climate Zones 4 through 6.

Sampling can be defined in the code, but another option is to author an Australian Standard or private industry standard that describes sampling guidelines. Generally codes will not refer to a privately-authored standard such as a set of industry guidelines, although the Air Infiltration and Ventilation Association could author such a standard.

Sample Modified Language from IECC 2015 (Proposed) for New York State

For buildings with more than seven units, a sampling protocol may be allowed by the code official. The sampling protocol requires that units be grouped into sample sets of seven units, representative of all unit types. All units of the first sample set shall be tested without any failures. Upon successful testing of the initial sample set, remaining units may be tested at the rate of one per sample set. If any tested unit fails compliance with the maximum allowable air leakage rate, two additional units in the same sample set must be tested. If additional failures occur, all units in that sample set must be tested. In addition, all units in the next sample set must be tested for compliance before sampling of further units can be continued.

The existing Australian Standard AS-NZS ISO 9972-2015 is not entirely clear on how the building should be prepared for a test. Similar to the IECC, test conditions would have to be defined in the code such as this:

Sample Language from IECC 2012

During testing:

  • Exterior windows and doors, fireplace and stove doors shall be closed, but not sealed, beyond the intended weather-stripping or other infiltration control measures;
  • Dampers including exhaust, intake, makeup air, backdraft and flue dampers shall be closed, but not sealed beyond intended infiltration control measures;
  • Interior doors, if installed at the time of the test, shall be open;
  • Exterior doors for continuous ventilation systems and heat recovery ventilators shall be closed and sealed;
  • Heating and cooling systems, if installed at the time of the test, shall be turned off; and
  • Supply and return registers, if installed at the time of the test, shall be fully open.
E. Mandatory testing to 10 ACH50

By 2022, testing of all residential construction would be required to a relatively easy 10 ACH50 standard or equivalent. The standard could possibly be adjusted, as it is in the IECC, for differences in climate. Even southern states like Florida, Texas, and Arizona, which have similar climates to Australia, have a standard of 5 ACH50 in the IECC.

F. Mandatory testing to 5-7 ACH50

By 2025, testing of all residential construction would be required to the long-term goal of 5 ACH50 standard or equivalent, perhaps more stringent in cooler Australian climate zones.