NZS 4431:2022 – Engineered fill construction for lightweight structures strengthens the foundation for modern buildings

NZS 4431:2022 – Engineered fill construction for lightweight structures is an update of the 1989 standard, with significant changes reflecting over thirty of years of improvements in geotechnical investigation, design and construction practice, test methods and environmental, consenting and health and safety obligations. 

The standard plays a fundamental role in ensuring engineered fill construction is delivered safely and provides a stable foundation for lightweight residential and commercial buildings, and their associated infrastructure. Current needs have been factored in including sustainability in design and climate change considerations, planting and revegetation, cultural heritage and archaeology and latest material types.

For geotechnical designers, contractors and certifiers

NZS 4431 is for those working across the construction project lifecycle – from the geotechnical designers responsible for the design and specification of earthworks projects, to the contractors responsible for implementing those specified works and finally the certifier responsible for confirming that construction is in accordance with the design, consent conditions, and earthworks specification.

Consensus-built for broad perspectives

Developed through Standards New Zealand’s trusted and internationally-used consensus approach, committee members provided expertise from engineering geologists and geotechnical engineers, design consultancies, councils, civil engineering contractors, heritage, health and safety, regulation and testing, and academia and research. 

The foundation for compliance

Forming the core of Building Code compliant foundations and generously sponsored by the building regulator Building Systems Performance (BSP), NZS 4431 is not a specification, but rather a framework reflecting the iterative processes used by the geotechnical designer, contractor and certifier. 

To comply with this standard, certified engineered fill construction needs to meet the requirements of a project- and site-specific earthworks specification, supported by appropriate design documentation, engineering drawings, quality assurance and testing requirements, and building and consent conditions.

Driving consistency and minimising the learning curve

P4431 Committee Chair Ross Roberts, Head of Engineering Resilience for Auckland Council, says, ‘NZS4431 is a critical element in the system that ensures buildings in New Zealand are safe. The updated standard brings a balance of appropriate minimum requirements and the flexibility needed to accommodate earthworks across the varied geology of New Zealand. 

It achieves this by setting out the process to define a robust earthworks specification, with the core elements pre-defined for commonly encountered conditions and the flexibility to amend these where appropriate to suit other site conditions. This standard will be supported by a template earthworks specification, due to be published for consultation by the New Zealand Geotechnical Society in the coming months.

The committee’s core intent was to drive consistency in earthworks specifications. This should make it easier to comply with those specifications by reducing variability between projects thereby minimising the learning curve – and the number of mistakes and amount of rework – on each project, reducing costs and project delays. Providing guidance on how to develop these specifications, and a template to follow, should encourage good practice, resulting in more robust and sustainable earthworks with fewer failures.’

Sponsored to help you meet the Building Code

NZS 4431 forms part of the package of more than 120 standards sponsored by Building System Performance, to help those in the construction sector to do the right thing. By bringing together New Zealand’s various practical and theory-based experts from across the industry, all in consensus on good practice, NZS 4431 should help keep people safe and buildings standing for generations to come.

NZS 4431:2022 – Engineered fill construction for lightweight structures is available to download from Standards New Zealand from the end of May.

https://www.standards.govt.nz/get-standards/sponsored-standards/building-related-standards/