Part F6 Condensation management

The Objective of this Part is to safeguard occupants from illness or loss of amenity as a result of excessive internal moisture.

Part F6 aims to limit the amount of condensation that can accumulate within a building by requiring that water vapour be extracted to a point external to the building. It only applies to residential building classifications which are considered to be more susceptible to the accumulation of moisture due to the building’s intended function and use. The majority of moisture within a building is produced from washing (bathrooms and laundries) and cooking.

Condensation is a physical phenomenon that occurs naturally wherever and whenever the physical conditions are conducive. Mould often grows where condensation forms within the built environment. The principle physical drivers are air pressure, temperature and humidity. These same physical conditions can occur within all built structures, in all climate types within the building (its internal environment), within its intermediate zones (subfloor and roof space zones) and within the building structure (floor, walls, ceilings and roofing materials). These natural processes cannot be stopped from occurring where these conditions exist. However, buildings can be designed, constructed and used in a way that manages vapour pressure, condensation risk and subsequent mould growth.

Human occupation of a residential building creates approximately 10 litres of water vapour per person per day. In an average family home with two adults and one child this equates to 30 litres of water vapour within the built fabric per day. This comes from people breathing, cooking, boiling water, washing and bathing. The shift from unconditioned to conditioned homes and the requirements for wall and ceiling insulation have significantly impacted on the internal climate of homes and the potential for condensation to occur. This is primarily due to less air changes within the home and occupants being less likely to open windows and doors when the air-conditioning is running. Modern buildings are also much better sealed due to advances in building materials and systems.

Interstitial condensation can affect the structural integrity of a building but its presence often goes undetected until such time as the cost to remedy becomes significant. The most effective means to reduce the problem of interstitial condensation is to provide a pathway for water vapour that avoids the accumulation of condensation. To remove the risks associated with condensation and to maintain indoor air quality, moisture laden air needs to be removed from the building and expelled out to the external environment.

The design, construction and use of a building can create conditions that lead to a building experiencing prolonged periods of damp, which leads to poor indoor environmental qualities, (potentially affecting occupant health) mould, and building degradation. Occupant behaviour, for example opening windows and doors to ventilate the building, can significantly impact a building’s indoor air quality but cannot be regulated by the NCC. The NCC’s Part F6 Condensation Management requirements were included in the NCC to assist in addressing the risks associated with condensation in residential buildings.

A building is to be constructed to avoid the likelihood of excessive internal moisture accumulating within the building structure.

Class 2 buildings and Class 4 parts of a building must be designed to mitigate the risks associated with the amount of moisture that accumulates internally.

FV6 describes a means of verifying that the effects of internal moisture will not accumulate to a degree which would detrimentally impact the health, safety or amenity of a building’s occupants as described in FO6.