Part J5 Building sealing

Where a solution is proposed to comply with the Deemed-to-Satisfy Provisions, J2D1 clarifies how compliance with Parts J2 to J9 achieves compliance with J1P1 to J1P4.

Where a Performance Solution is proposed, the relevant Performance Requirements must be determined in accordance with A2G2(3) and A2G4(3) as applicable. (See commentary on Part A2).

The Deemed-to-Satisfy Provisions, including those related to house energy rating software, described are limited to the most common forms of construction and the simplest forms of buildings. It is expected that the more innovative construction techniques and the more complex buildings will be designed and assessed using a performance approach.

A major consideration in developing the measures was the likelihood of a building being heated or cooled by an air-conditioning system, and whether the Deemed-to-Satisfy Provisions should assume this to be the case, or only apply the provisions if a heating or cooling system is installed. It is recognised that most Class 3, 5, 6 and 9 buildings and some Class 7 and 8 buildings are heated or cooled, and this is the basis of the provisions. Consideration was also given to the fact that although the first owner may be prepared to ‘manage’ their building in the appropriate manner, the next owner or tenant may not, and instead may install air-conditioning.

Because of the performance-based structure of the NCC, a Performance Solution may be proposed instead of the Deemed-to-Satisfy Provisions.

J5D2 does not apply where the only conditioning is provided by an evaporative cooler or to openings necessary for the safe operation of a gas appliance.

A building that is conditioned by heating or refrigerative cooling needs to be sealed to conserve energy but one that is conditioned by evaporative cooling does not need to be sealed as windows or doors would need to be opened anyway in order to provide the relief for the ventilation air. However, if the building is in climate zones 4, 6, 7 or 8, or has a refrigerative cooler, then it has to be sealed because of the likelihood of heating during colder periods or to avoid the loss of cooled air when the refrigerated cooler is running.

The Deemed-to-Satisfy Provisions of Part J5 do not apply to Class 8 electricity network substations as these buildings are not required to be air-conditioned for the purposes of Section J. See the definition for air-conditioning. The air-conditioning systems of these buildings are instead designed to maintain the efficient operation of sensitive electrical equipment.

Ventilation for safe operation of a gas appliance is not covered by the NCC, but is addressed by other legislation. Appropriate ventilation for gas appliances can be obtained from the relevant legislation, reference standards and product installation manuals.

Unique to this Part is that as air-conditioned buildings are often pressurised by the introduction of outside air through a mechanical supply system, it may not be necessary to seal the building to the same degree as for an un-pressurised building.

The requirements of this Part are to be read in conjunction with the fire safety requirements in Part G2.

A solid-fuel burning device is a heater that burns material such as timber, coal and the like. This provision does not apply to gas and liquid fuel burning devices.

Roof lights that are openable must be sealed when closed in order to restrict the loss of conditioned air to the outside environment. It is assumed that most of the habitable rooms in residential type buildings in the cooler climate zones will be heated by installed or portable heaters. However, if a non-habitable room is conditioned, either cooled or heated, then it must also be sealed. For the hotter climate zones, the roof lights need be sealed only if conditioning is being installed. 

An external door opening to a conditioned space must also have a device to prevent significant amounts of conditioned air being continuously lost. This only applies to conditioned spaces greater than 50 m2. Devices that may be installed to comply with this requirement may include an airlock, self-closing door, or revolving door. Provisions for people with a disability should also be considered when selecting the device.

There are a couple of exemptions to these requirements, such as for roller shutter doors or the like, that are used for out-of-hours security purposes only, i.e. when conditioning is not operating. Another exemption has been granted for the main entrance to a café, restaurant or open front shop that has a 3 m non-conditioned zone. Where staff are carrying trays of food or drink it may be unsafe to require an airlock, self-closing door or sliding door.

The sealing of exhaust fans applies to the same spaces and in the same climate zones as described for roof lights. It also only applies to “miscellaneous” exhaust fans, such as smaller fans used for domestic kitchen exhaust. The provisions do not apply to smoke exhaust fans and the like. The term “miscellaneous” is comparable with the use of this term in AS 1668.1 for certain air-handling systems.

A miscellaneous exhaust fan is considered to be adequately sealed if it is fitted with a self-closing damper or similar sealing device.

The sealing of roofs, walls and floors applies to the same spaces and in the same climate zones as described for roof lights. For the purposes of J5D7, a suitable seal includes expanded foam, rubber compressible strip, caulking or other gap filling material.

The acceptable solution of a “close fitting internal lining system” is considered to include an allowance for minimum gaps in internal linings for thermal movement at wall, floor and ceiling junctions.

Similarly to exhaust fans, an evaporative cooler represents a large opening in the building envelope. This opening needs sealing when the evaporative cooler is not in use, such as in the winter when a heating system may be operating.