Certifier requirements for corrosion protection of steel posts

Key information

• Certifiers must meet corrosion protection requirements of Clause 6.3.9 of ABCB Housing Provisions 2022.
• Posts must be designed, manufactured and installed in accordance with the Building Code of Australia (BCA) and relevant Australian Standards.
• There are significant impacts when corrosion protection of steel posts of buildings with suspended flooring systems is inadequate.

Introduction

Steel posts are a popular alternative to traditional concrete footings. They provide cost-effective, and environmentally friendly options for builders.

However, a significant number of class 1a buildings within coastal areas of Eastern Australia have been constructed on steel posts without due consideration of the corrosivity of the location, resulting in inadequate corrosion protection.

Impacts of inadequate corrosion protection of steel posts of buildings with suspended flooring systems include:

• early and costly re-stumping
• rectification of cracked floor and wall tiles to bathrooms
• rectification of damage to waterproof membranes in wet areas
• re-fitting doors throughout the house including internal and external doors
• re-painting the house where cracks appear on the inside and outside the house
• replacing or repairing hot- and cold-water connections, including stormwater, sewerage pipes and electrical connections

To help reduce these negative impacts and safety issues, certifiers must meet corrosion protection requirements of Clause 6.3.9 of ABCB Housing Provisions 2022. These requirements differ based on the stage and/or type of construction. 

Requirements at the construction certificate stage

Determine the corrosivity category of the location of the building 

Based on the building location, certifiers must determine the corrosivity category as either: 

• low
• medium
• high
• very high. 

In the table below, a figure has been included below for reference.

For further information on corrosivity environments, refer to Section 3 of AS 4312:2019 Atmospheric corrosivity zones in Australia.

Ensure architects and engineers designs specify suitable corrosion protection of the structural posts

The corrosion protection methods for the posts should be developed based on the corrosivity environment that has been determined. 

For Hot Dip Galvanised (HDG) steel members

The table below shows which readily available materials meet the requirements of Table 6.3.9a of ABCB Housing Provisions 2022. If no certificate is available, measure the HDG coating thickness. HDG coatings of all types are relatively straightforward to assess via use of a non-destructive coating gauge, even if no certification from the supplier is available. 

Requirements for duplex and painted protective coatings

Document the certificate from the painter, or document evidence from the builder of the materials used and ensure the overall coating thickness is measured. Paint systems must be in accordance with AS/NZS 2312.1 2014 Guide to the protection of structural steel against atmospheric corrosion by the use of protective coatings. 

Requirements for paint coatings

For paint (including duplex coatings), evidence of the surface preparation, paints used and the coating thickness for each type of paint will be required to assess conformance. Practically, a certificate from the paint applicator (if done in the factory), or evidence of the paint materials used by the builder (if done on-site) will be required.

Certifiers are encouraged to reference section 12 of the Environmental Planning and Assessment (Development Certification and Fire Safety) Regulation 2021 when advising anyone involved in the design phase of what information the certifier considers necessary for the application to be considered. 

Requirements at the occupation certificate stage

Ensure that the builder can demonstrate that the works have been constructed in accordance with the approved designs.  This can be in the form of a statement from the builder with supporting evidence of the materials used.

Where the steel has been cut, the builder must confirm/verify the steel thickness and class of galvanization. They must also demonstrate that all cut edges are repaired to the standard of the original corrosion protection. Look for rust or repairs to welded areas, cut ends, and other damage.

Obtain evidence that the repairs provide equivalent protection. This may include sighting the paint that was used or, for large areas of damage, measuring the coating thickness in the repaired area. If the damage has not been repaired, the product does not meet the requirements.

Certifiers are encouraged to reference section 38 of the Environmental Planning and Assessment (Development Certification and Fire Safety) Regulation 2021 when advising anyone involved in the design phase of what information the certifier considers necessary for the application to be considered.