Not all wall systems are required to have a dedicated ventilation strategy. As a rule of thumb, wall systems not incorporating a dedicated drainage cavity should only be used in locations where the rainfall is below 500mm per annum, which limits the use of these systems to the driest inland areas of Australia.
Put simply, a ventilation strategy to induce drying within the cavity of a wall system is recommended across most populated areas of Australia, where annual rainfall is greater than 1000 millimetres a year. This is particularly true for the Australian eastern seaboard.
From a design perspective, wall systems are often considered to be unventilated as there are benefits from an R-value perspective. However, some systems such as brick veneer or rainscreen systems are required to be ventilated and should be nominated as either a slightly ventilated or well-ventilated cavity.
Further definitions for cavity ventilation are found within AS/NSZ 4859.2: 2018 - Thermal insulation materials for buildings Is used and is a primary reference within Part J1 building fabric. Also, AS 3700:2001: Masonry structures provides further requirements for the design and construction of masonry wall systems.
In principle, where a dedicated ventilation drainage strategy is applied to a wall system, it's aim should be to induce the maximum amount of airflow through the cavity to dry out any water-sensitive materials so they can perform optimally and maintain their durability over time.