Don't expose yourself

Are you building in a coastal region, high rainfall zone or near a heavy industrial area? Then you may be aware that special consideration is required for your materials and products to ensure building quality. 

What about general suburban areas or new greenfield estates? Well, it may come as a surprise that these buildings also require special consideration and detailing for materials, from steel lintels, brick ties, reinforcement, roofing and gutters to mortar and bricks, concrete mix and cement type, fittings, fixtures, as well as bracing for framing.

Use the wrong product or in the wrong circumstance, and you can have a detrimental effect on the long-term durability of the building. However, understanding and following the National Construction Code (NCC) and Australian Standards for corrosion and compatibility requirements can save you potentially thousands of dollars in rectification costs.

Externally located building elements are more prone to corrosion than those located internally for homes built in coastal areas.

 

Corrosion environments

As with most aspects of building codes and standards, different parts of Australia are divided into maps or zones to group specific locations with similar characteristics or risk profiles. Accordingly, requirements to treat particular risks for buildings in those areas are prescribed in the NCC and relevant Australian Standards.

The first factor to consider is whether the building is in a coastal or inland location because areas close to the coast can be exposed to relatively high concentrations of airborne sea salt. This can be even more severe when located nearer to breaking surf in comparison to sheltered bayside areas.

If the home will be constructed in a coastal region, then the location of the building element within the building needs to be considered. Externally located building elements are more prone to corrosion than those located internally. 

Builders must also note whether the building is to be located near heavy industrial areas because this will also influence the type of corrosion protection requirements for relevant building elements.

If a building is to be located near heavy industrial areas, this will influence the type of corrosion protection requirements for relevant building elements.

Location, location, location

When specifying corrosion protection for products, such as lintels, sheet roofing tie downs or wall ties, you need to have a firm understanding of: 

• internal locations, which are areas within a building envelope that are kept permanently dry (closed and non-ventilated roof spaces can be considered internal locations); and
• external locations, which are the areas outside the building envelope that are exposed to repeated wetting (sheltered areas may be treated as external locations).

Don’t be fooled into only thinking literally in an ‘internal’ and ‘external’ sense though, as the NCC has specific criteria in determining what is considered an internal and external area.

For example, elements that may exist internally in a roof or wall cavity may actually be classified as an ‘external’ location and external corrosion protection requirements will therefore apply. This will include internal locations subject to moisture, such as a steel beam that is in close proximity to kitchen or bathroom exhaust fans. While it is technically located in a permanently dry location, protection specified for external locations will be required due to its potential exposure to repeated moisture.

Another key consideration is compatibility requirements of materials. To prevent corrosion due to adverse chemical reaction of materials used, the NCC sets out a range of provisions to ensure that the metal roofing and other materials that come into contact with it, i.e. fasteners, flashings and cappings, etc. are compatible with each other. 

‘Too often we are seeing structural tie down and bracing products substituted for thinner and/or lower grade hoop iron without proper consideration of the impact this has on capacity, performance and compliance’

– Adam Dawson, Pryda ANZ Technical Manager

Scope and limitation – don’t just assume it will be OK

Selection and use of the correct products for the building, particularly for structural elements such as bracing, tie downs, fixtures and connectors, is a complex area. It is much more involved than just looking at whether standard, galvanised or stainless steel coatings or fixtures should be used.

There are a large number of Australian Standards and NCC provisions that contain corrosion, compatibility and exposure and structural capacity requirements that affect the selection, design and construction requirements for a broad range of building elements.

Therefore, don’t just assume the same fittings, fixtures and coatings to metal and steel products or bracing, roofing and flashings will be suitable for all buildings and locations. Close attention is required to ensure the correct detailing of building elements are chosen and used in the situations they are prescribed for.

Adam Dawson, Technical Manager at Pryda ANZ, says that steel strap cross bracing is a common form of bracing material, but questions how building professionals can tell if the products they’re using are the correct ones for use as a structural brace or tie down that complies with relevant Australian Standards.

‘Too often we are seeing structural tie down and bracing products substituted for thinner and/or lower grade hoop iron without proper consideration of the impact this has on capacity, performance and compliance,’ he says.

AS1684, the timber framing standard, requires the nominal size of the metal straps to be 30x0.8mm, with a minimum net sectional area of 15mm2 for 1.5kN/m bracing units and 21mm2 for 3kN/m units. The minimum grade of steel strap is to be G300.

‘The NCC at Part A5 specifies the product evidence requirements to demonstrate that the material/product will meet the requirements of the NCC,’ Adam explains. ‘One way to find out if a product meets these requirements is to get the product technical statement for the bracing. This will specify how and when it can be used and the performance requirements or relevant standards that is satisfies.

‘Therefore, to ensure your frame, and in turn your bracing, complies, you need to ensure you are across the NCC and Australian Standards requirements in selecting and using the correct bracing and tie down materials, and checking the product documentation to be confident that it complies.’

Another important aspect of checking your product technical sheets is to look for any limitations or scope of use of products because often they may contain specific conditions or restrictions on the use of the product.

With the NCC and standards constantly under review, you need to stay on top of the changes to ensure you are using the right materials. You don’t want to get caught out by any changing specifications. 

With all of this in mind, the old adage of measure twice, cut once is a useful principle for selecting and using building products – check the requirements and documentation first before buying and applying.

This principle can save you many headaches and costs in the long run.

Not all bracing is equal

According to Pryda, builders need to be careful when selecting steel strap for bracing to make sure it’s fit for purpose. Strap sold as ‘hoop iron’ may not meet the size, thickness and strength requirements for structural bracing in AS1684, and if the nail and tensioner holes are not correctly staggered it may not have enough net cross-sectional area to carry the bracing loads. 

A suitable product will have technical data available from the supplier that states how it should be used in and if any other products (such as stud straps) or structural details are required to achieve compliance with the NCC for each specific application. 

Building quality and compliance

Over the past few years, the issue of building quality and compliance has been discussed in length, in particular in the wake of some high profile building issues for high-rise buildings, both in Australia and overseas.

At the 2020 HIA National Policy Congress, a set of ‘Building Pillars’ or principles were endorsed and will form a key part of HIA’s advocacy and strategic approach to building quality, including forming practical solutions in promoting improved building quality, with the support of industry. HIA’s Building Pillars focus on the following:

• Raising the profile of our industry’s high quality work and services
• Practitioners and industry culture
• Building regulatory system
• Role of state and territory regulators
• Building products – conformance and compliance
• Building codes and standards
• Building approval documentation and specifications
• Tools and mechanisms to support compliance
• Further information on these Pillars can be found here.

HIA provides a range of support services to help members navigate the plethora of requirements that apply to building a house, and will continue to encourage a culture of ongoing enhancement of skills, knowledge and experience within the industry. Throughout 2021, and leading up to the publication and adoption of NCC 2022, HIA will also be developing a range of resources, supporting tools, and awareness and education activities to inform industry about the new changes and requirements.

This article on corrosion protection requirements is the third HOUSING instalment for our series on building quality. For further reading, see:

• The winds are changing
• On the right footing