Condensation Management is a new introduction to the NCC 2019 - Vol 1, laid out in Section F - Health and Amenity. Found within Part F6 Condensation Management, the Performance Requirements for Condensation Management are set out in FP 6.1, aiming to deal with the risks associated with water vapour, condensation and the potential impact on occupant health. Here, sole-occupancy units for Class 2 buildings and Class 4 part of a building are required to be managed within defined condensation management strategies.
“In a sole-occupancy unit of a Class 2 building or a Class 4 part of a building, risks associated with water vapour and condensation must be managed to minimise their impact on the health of occupants.”(FP6.1)
As always within the NCC 2019 – Vol 1, to meet the Performance Requirements, you are provided with Deemed-to-Satisfy and/or Performance Solutions. For the Deemed-to-Satisfy Solution, the building envelope is picked up in F6.2 Pliable Building Membrane while the Performance Solution is managed via a Verification Method within FV6 Condensation Management.
F6.2 Pliable Building Membrane
Focusing on Climate Zone 6, 7 and 8 and only applicable to a sole-occupancy unit of a Class 2 building and a Class 4 part of a building, F6.2 Pliable Building Membrane provides a Deemed-to-Satisfy Solution for wall systems only.
“(a) Where a pliable building membrane is installed in an external wall, it must—
(i) comply with AS/NZS 4200.1; and
(ii) be installed in accordance with AS 4200.2; and
(iii) be a vapour-permeable membrane for climate zones 6, 7 and 8; and
(iv) be located on the exterior side of the primary insulation layer of wall assemblies that form the external envelope of a building.”(F6.2)
(b) Except for single skin masonry and single skin concrete, where a pliable building membrane is not installed in an external wall, the primary water control layer must be separated from water-sensitive materials by a drained cavity.
Using the Standards AS / NZS 4200.1 and 4200.2, F6.2 Pliable Building Membrane prioritises vapour diffusion control and sets the mandatory application of Class 3 or Class 4 vapour permeable membrane. So simply put, projects within Climate Zone 6, 7 and 8, you are now required to specify and install a vapour-permeable membrane.
There is one exception to this provision that focuses on the ability for a Wall System to manage condensation through the separation of a drained air cavity. Drained air cavities need to be ventilated in order to mitigate condensation risk successfully. Such strategies are not typical or preferable in most cases as the durability of a system that has no water control layer interior to a drained cavity or one that is a vapour barrier is likely to result in condensation within buildings that have high moisture rates.
FV6 Condensation Management
For projects wanting to meet the Performance Requirements of FP6.1 Condensation and water vapour management, FV6 Condensation Management sets out a Verification Method focused on undertaking hygrothermal modelling of a wall system. The aim is to ensure that there is no impact on the health of occupants as a function of the overall water control layer features of a wall system.
While there is no stipulated required outcome from the hydrothermal modelling Verification Method, the expectation would be that any water-sensitive material and the build-up of water content over time would need to be assessed. The outcome would further be supported by numerical evidence to show that moisture remains at levels that don't allow for the onset or continual growth of mould.
“Compliance with Performance Requirement FP6.1 is verified when modelling that assesses the effects of—
(a) indoor and outdoor temperature and humidity conditions; and
(b) heating and cooling setpoints; and
(c) rain absorption; and
(d) wind pressure; and
(e) solar radiation; and
(f) material hygrothermal properties,
determines that moisture will not accumulate—
(g) interior to the primary water control layer within a building envelope; or
(h) on the interior surface of the water control layer.”(FV6)