Condensation management webinar – questions and answers

Each webinar provided information relating to that topic including:

• the key changes in NCC 2022
• the new mandatory requirements
• an overview of available compliance options
• when the changes will be adopted
• tips and examples
• how to find more information and support.

You can access video recordings of the webinars on the ABCB YouTube channel.

Each webinar also provided the opportunity for attendees to ask questions about changes to NCC 2022. We could not provide answers to all questions asked during the webinar sessions, so this article provides answers to commonly asked questions from the condensation management webinar.

While we have endeavored to capture the intent of most questions asked during the webinar, there may be some that are not included in this article. This is likely due to the question being outside the scope of the NCC or not covered in the condensation webinar. 

Are closed cell insulation or reflective foil products allowed by the new condensation DTS Provisions for pliable building membrane?

The DTS Provisions for condensation management do not prevent the use of any products. However, they do set minimum requirements, such as vapour permeability, in Part 10.8 of the Housing Provisions Standard (Housing Provisions) or Part F8 (NCC Volume One) they must achieve if being used as pliable building membranes. 

If I use a fan more powerful than the minimum specified in the DTS Provisions, does the make-up air free area need to be greater than that nominated in 10.8.2(5)(a) of the Housing Provisions?

No. To comply with the DTS Provisions for make-up air, you need either 14000mm² of free area (10.8.2(5)(a)) or use AS 1668.2.(10.8.2(5)(b)).

Does a room with natural ventilation in accordance with 10.6.2(a) of the Housing Provisions (F6D7 in NCC Volume One) require mechanical ventilation?

No. Mechanical ventilation is not required if a room is naturally ventilated in accordance with 10.6.2(a) of the Housing Provisions (F6D7 in NCC Volume One). Yet, if a naturally ventilated room has mechanical ventilation installed, then it must meet 10.8.2 of the Housing Provisions (F8D4 in NCC Volume One). Note, this is only relevant when using a DTS Solution. A Performance Solution is also suitable to show compliance.

Do rooms with skylights or lightwells need interlocking between the exhaust and light switch?

Yes, interlocking is required when using the DTS Provisions. This interlocking aims to maximise the chance of using the exhaust. This only applies to rooms that are not naturally ventilated.

How do the DTS Provisions for condensation management apply to external walls which are single skinned (such as insulated panel or walls with a cladding direct fixed to studs), or where drained cavities can’t be installed (such as precast cladding with internal stud wall behind)?

The best way to answer this question is to summarise the DTS Provisions for condensation management. There are essentially two options:

1. install a pliable building membrane as outlined in 10.8.2 of the Housing Provisions (F8D3 in NCC Volume One), or
2. install a drained cavity.

Single skin masonry and single skin concrete walls are exempt from these requirements.

This means that if your wall system doesn’t comply with (1) or (2) above, then you will need a Performance Solution, such as Verification Method H4V5 (F8V1 in NCC Volume One) to show compliance.

How do I apply the DTS Provisions for condensation management to a low-pitched roof that has no eaves?

Let's look at NCC Volume Two since NCC Volume One is similar. Table 10.8.3 of the Housing Provisions provides ventilation opening options for 3 different roof pitches:

1. Roofs less than 10 degrees - 25000 mm²/m ventilation opening provided at two opposing ends
2. Roofs greater than or equal to 10 degrees and less than 15 degrees - 25000 mm²/m ventilation opening provided at the eaves and 5000 mm²/m ventilation opening at high level
3. Roofs greater than or equal to 15 degrees and less than 75 degrees - 7000 mm²/m ventilation opening provided at the eaves, 5000 mm²/m ventilation opening at high level and an additional 18000 mm²/m at the eaves if the roof has a cathedral ceiling.

Note: ‘high level’ openings are openings provided at the ridge, or less than or equal to 900 mm below the ridge or highest point of the roof space (measured vertically).

This means for low pitch roofs (those less than 10 degrees) eaves are not needed to comply with the DTS Provisions. Instead, ventilation openings of 25000 mm² must be provided at two opposing ends to meet the DTS Provisions. If providing ventilation at opposing ends isn't possible (for example, to meet weatherproofing requirements), then a Performance Solution such as H4V5 (F8V1 in NCC Volume One) could be used.

If you want to know about NCC condensation management watch the Condensation management webinar or download the Condensation in Buildings Handbook.