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NCC 2019: Condensation Management

As today’s NCC 2019 broad range of commitments land and are ready for preview, we can finally say Condensation Management is in and will be mandatory by May 2019.

If you haven’t got a copy yet, grab one here.

More formally, Section F - Health and Amenity has been extended to now include Part F6, setting forth a performance requirement to now manage condensation and water vapour in Class 2 (Multi-Residential) and 4 (a dwelling or residence within a building of a non-residential nature) buildings.

Is it a valuable addition to the NCC code, what will it change and who will it impact? Let's have a look!

Do we need further management of condensation and water vapour?

First up, an easy one…...is it required? 100% it is!

For anyone exposed to post-construction remediation, water vapour and condensation issues have increased exponentially in our single and multi-residential markets. For those looking for a career in mould management, the market is hot!

With increased moisture in building components and high internal air humidity, there is no debate that the growth of microorganisms such as mould and bacteria impact both health and aesthetics and are on the rise.

In addition, reduced thermal resistance, material decay and even mechanical stress are also a real result of uncontrolled moisture, so getting this right is a must!

So, with a big tick in the ‘required’ box, what will it change?

What’s new?

This is a biggie, so we need to crack into the detail. Deep breath!

FP6.1 states “……. risks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants” and is met by either a Deemed-to-Satisfy (DTS) provision (as usual) or a Verification Method. Let’s unravel the DTS provision first.

The DTS provision has multiple focus areas, that can all have a partial impact on water vapour and condensation risk. These include:

  • F6.2 - Pliable building membrane

  • F6.3 - Flow rate and discharge of exhaust systems

  • F6.4 - Ventilation of roof spaces

This makes absolute sense as today’s post construction remediation challenges are often focused on a combination of unknown façade airtightness, poor or no vapour control, a lack of or uncontrolled ventilation, higher internal moisture loads or other.

F6.2 - Pliable building membrane

For building membranes (F6.2), the DTS provision references 2 parts of a standard, AS/NZS 4200.1 and AS 4200.2, both of which were updated in 2017 and focus on pliable building membranes. The former is intended for use in assessment and classification of pliable building materials, the later, for the installation of said materials.

Of immediate interest is that F6.2 clearly stipulates what educated suppliers have been saying for years, that colder climate zones 6 (Melbourne) ,7 (Canberra) and 8 (Hobart) must have vapour permeable membranes located on the exterior side of the primary insulation layer to let moisture out.

In other words, AS/NZS 4200.1 sets forth important vapour control classifications that either allow or restrict the transfer of water vapour across the membrane. Meaning, a supplier will need to have tested their product to be in 1 of 4 classes of vapour control based on its level of vapour permeance (µg/N.s), as they typically do anyway. If in vapour control class 1 – 2, a product restricts water vapour across the membrane and is determined as a vapour barrier. While classes 3 – 4 determines that a product allows water vapour transfer and thus is vapour permeable or semi- permeable.

Using the image below as an incomplete view of anonymous products on the Australian market, we can quickly see that many products are below the critical red line (Class 3 - semi- vapour permeable) and thus cannot be used in the DTS provision come May. And for those looking for the lowest moisture risk products on the market, you should be aiming to be above the Class 4 green line and at vapour permeable products only. 

So, for Class 2 and 4 projects in climate zones 6 (Melbourne) ,7 (Canberra) and 8 (Hobart) using building membranes, a review of which membrane being supplied by the subcontractor is now a must!

F6.2 - Flow rate and discharge of exhaust systems and F6.4 - Ventilation of roof spaces

Not my area of expertise but the logic here is again sound. For the sake of keeping you reading until then end, i will skip some of the details and focus on the the primary points.

With higher moisture sources in smaller apartment volumes, it is fundamental to the health of occupants that stale or polluted air gets extracted at minimum flow rates and is safely discharged not into a ceiling or closed roof spaces, but to the outdoors or to large spaces that are very well ventilated.

Today, one of the key areas I have seen in the multi-residential market is the combination of inadequate design assumptions around ventilation and the reliance on the behaviour of occupants.

Will an occupant leave the extractor on in the bathroom after a 10 minute 60 degree shower? Will they use the extractor in the kitchen while boiling some spuds? Are they aware that windows sometimes need to be opened to release moisture from the apartment and bedrooms are the first place where condensation typically occurs?

While the DTS provisions don’t go anyway to dealing with how a space is used by an occupant, and nor should it, it does begin to wrap up these condensation and water vapour issues so we can begin to consider them in more depth.

FV6 Verification Method

And what if you cannot meet all the detailed DTS provisions or want to see if you can get away with a Class 2 membrane? We have a Verification Method of course!

Put simply, we have the option to undertake hygrothermal modelling to determine that moisture will not accumulate interior to the primary water control layer within a building envelope or on the interior surface of the water control layer.

To offer evidence of no such accumulation over time, we need to model the following:

  • indoor and outdoor temperature and humidity conditions

  • heating and cooling set points

  • rain absorption

  • wind pressure

  • solar radiation

  • material hygrothermal properties

Where the Verification Method gets interesting is that while the DTS provisions are holistic, considering multiple sources of moisture vapour and transfer, we seem to be only encouraged to look at typical wall build-ups when modelling?

I guess it will be up to engineers to gauge the best approach and for building surveyors to weigh in on how the code should be interpreted, but surely you cannot manage condensation and water vapour in Class 2 and 4 buildings by simply modelling a wall build-up?

A great introduction to the NCC

Semantics and methodologies aside, while the usual opportunities for beneficial interpretation on a project by project basis remain embedded into the NCC, the focus over the next few years for design teams will need to consider the management of condensation and water vapour to a much higher degree.

I think this is great news for design teams, building owners and Australian construction in general. Well done to all that contributed to getting this into NCC 2019!


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