ABCB Roadshow 2024: Condensation Mitigation

Condensation and subsequent mold growth in the residential parts of buildings presents health risks to occupants and can degrade building elements prematurely.

Building upon the condensation requirements introduced into NCC 2019 and NCC 2022, these proposed changes further improve condensation mitigation for external walls and roofs.

This includes mandatory cavities in cooler climates and more stringent vapor permeability requirements.

They'll also align the NCC with approaches from other international codes and standards in countries with similar climatic conditions.

As well as mitigating the effects of condensation to reduce potential mold growth, these proposed changes also aim to address issues in the current provisions.

Practitioners have questioned the practical limitations to compliance and the clarity of the current provisions, particularly in relation to external wall construction and ventilation in roof spaces.

In developing these proposed changes, we consulted with a Technical Reference Group or TRG that included industry representatives, academic institutions, and state and territory governments.

We also worked with our peak technical committee, the Building Codes Committee, or BCC and other stakeholders, including experts in the fields of building physics, energy efficiency, and fire safety.

A range of factors including building issues both locally and in overseas jurisdictions, as well as hygrothermal modeling using NCC 2022 provisions as the baseline have indicated that there are latent condensation risks for external walls in certain climate zones.

So what exactly are the changes and where do they apply?

The proposed changes will cover four main areas.

Firstly, external walls in climate zones 1 to 5.

These climate zones cover places including Darwin, Brisbane, Mount Isa, Kalgoorlie, and Newcastle.

Here we're proposing changes to require that any control layer, sheathing or water barrier incorporated into the external wall achieve a certain vapour permeance.

This will be specified in table F8D3 in Volume One and Table 10.8.1 of the Housing Provisions and apply to an external wall with a drained and vented cavity.

Note that some types of external constructions in climate zone 1, Darwin and Cairns, for example, are exempt from this requirement.

You may be unfamiliar with the term vapour permeance, so I'll explain this briefly before we move on.

Vapour permeance is the degree that water vapor can diffuse or move through a material.

Continuing on, the second proposed change is to external walls in climate zones 6 to 8.

These climate zones cover places including Melbourne, Hobart, and the Alpine regions.

There are two changes proposed to the Deemed-to-Satisfy or DTS Provisions for external walls in these climate zones.

Firstly, that the wall has a drained and vented cavity, and secondly, that any control layer or barrier installed between the exterior side of the prime insulation layer and the cladding must have the equivalent of a class 4 vapour permeance as defined in AS4200 Part One.

Thirdly, for roof ventilation openings we're proposing to extend the current requirements to climate zones 4 and 5.

In climate zones 4 to 8 we're also proposing separate roof space ventilation requirements depending on whether the ceiling is parallel to the roof plane.

For changes to 10.8.3 of the Housing Provisions, we're proposing to include an example of how to calculate high level and low level ventilation openings.

And finally, we are proposing to extend the application of part F8 in Volume One to include hotels, hostels, and the like, which are Class 3 buildings.

And also aged care buildings, which are Class 9C buildings.

This table outlines some of the proposed changes to the vapour permeance requirements compared to NCC 2022.

In summary, NCC 2022 didn't have separate vapour permeance requirements for drained or vented cavities.

For the next edition we're proposing concessions that reduced the vapour permeance values for walls with cavities.

Also, direct fixed wall systems are no longer permitted in climate zones 6 to 8.

As our analysis demonstrated, there is condensation risk to walls in these climate zones.

Finally, we're maintaining the current requirements for climate zone 4.

What impacts could these changes have?

Cost benefit analysis we commissioned shows there's an overall national benefit of $400 million, but it varies across the country by climate zone and depends on whether a wall has a cavity or not.

Both tropical and cooler climates, so climate zone 1 and climate zones 5 to 8 show a significant overall benefit. In these climate zones walls with a drained and vented cavity show a net benefit of $217 million while walls without a cavity show a net benefit of $500 million.

In warmer areas like Brisbane and Central Australia, which are climate zones 2 to 4, the proposed changes will reduce problems, but the benefits don't outweigh the costs.

The cost benefit analysis shows a net cost due to the modeling predicting a lower baseline risk.

Overall, the consultation regulatory impact statement or CRIS shows that the increase in building construction costs would be below 1%.

Aside from the financial considerations, there will also be improved protection of building elements from degradation by moisture.

The proposed changes to the ventilation of roof spaces also align better with existing design and construction approaches in Australia, simplifying compliance.

The proposed changes to the external wall provisions strike a balance between community expectations, technical merit, and practicality.

They're also relatively easy to implement and allow practitioners some flexibility when designing and building external walls.

Finally, these changes could have significant positive health benefits as reducing occupants exposure to mold will lead to fewer upper respiratory tract symptoms such as bronchitis and asthma.

If you'd like to provide feedback on this proposed change, visit our dedicated PCD page, abcb.gov.au/pcd.

Here you'll find links to the draft changes for Volumes One, Two, and Three, and the Housing Provisions.

You'll also find links to support materials and technical documents to help you understand the proposed changes.

Finally, this page has a link to our consultation page where you can have your say.

The public consultation is open from 1 May to 1 July 2024.

We look forward to your input.