Finding the best of both worlds: Fire safety & moisture management in building façades

The 2017 Grenfell and 2014 Lacrosse tower fires sent shockwaves through the Australian design and construction industry. Independent inquests and regulatory reform followed, leading to amendments to the National Construction Code (NCC) and a ban on the use of combustible claddings by many state regulators.

Driven by the heightened demand for fire safety, the growing preference for noncombustible, non-permeable metal sheathing as a form of weatherproofing has made managing moisture levels within a building more difficult. Designers and specifiers need to understand the relationship between non-combustibility and condensation build-up so they can avoid the consequences of insufficient moisture control.

The Consequences of Insufficient Moisture Control

As water damage is often not immediately visible, insufficient moisture control can result in long-lasting building issues and potential health risks. Steel or timber frames, insulation, electrical wiring and other elements in the building can be compromised by water damage. Damp wood can lead to decay, fungal growth and termite infestation. Occupants may also be exposed to health risks related to toxic mould growth, bacteria and expansion of dust mine population.

Understanding the Relationship Between Non-combustibility and Condensation

Under the current weatherproofing and noncombustibility requirements in the NCC, the tendency has been to specify metal sheeting such as steel or aluminium on the outside of a structure. While this results in high levels of fire and weather resistance, it is difficult for water vapour to escape leading to condensation build-up.

Changes published in the NCC 2019

Volume One included a section pertaining to Condensation Management within Section F: Health and Amenity. To mitigate condensation, F6.2 provides that any external membrane applied to a project in Climate Zones 6, 7 and 8 must be vapour permeable.

Designers and specifiers should note that non-permeable metal sheathing, while meeting requirements for non-combustibility and weather resistance, will be unable to comply with the new standard for condensation management.

Promat

Established in 1958, Promat is a world leader in passive fire protection. With a wide range of solutions from mineral boards to fire shields for services and structural protection, the brand has earned a reputation for reliable, outstanding fire performance across all sectors and project types. The Promat range includes Weather Defence, an external weather resistant, highly breathable Rigid Air Barrier that meets the deemed-to-satisfy provisions for noncombustibility and vapour permeability.

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