Steel Reinforcing Mesh Supply Confidence

Steel Reinforcing Mesh Supply Confidence

Having confidence in mesh supplied for residential building

Aug 12, 2020


Over the last decade much has changed with regards to the steel reinforcing mesh that can be put into a residential foundation.

There has been much activity by Government to ensure compliant supply. Media discussion around issues some in the industry faced, regarding supply of compliant product, has also been significant.

On reading this article you will gain an understanding of why change was required, of the new compliance framework, and the different types of compliant mesh, so you can have confidence in what is specified & supplied.

In this article, we provide an overview of:

The background - What changed and why all the fuss?

Two significant events have driven changes in residential mesh manufacture and supply within NZ over the last decade. These are:

  • Learnings obtained from building performance during the Canterbury Earthquake
  • Challenges some in the industry faced with ensuring the newly developed Ductile Mesh was compliant with the new standards.

Following the Canterbury earthquakes BRANZ engineers & staff surveyed a number of houses, and as reported in the BRANZ Bulletin Aug 2012, it was found that slabs generally performed well, except where they:

  • were affected by liquefaction
  • were unreinforced
  • had reinforcement mesh that was too brittle
  • were not tied to the foundation.

Others also reported failures caused by a lack of mesh continuity, which was often caused by the mesh integrity being compromised by cutting control joints too deep. 

This ultimately resulted in changes to the building code and the acceptable solutions for reinforced concrete slabs. This is summarised in a short BRANZ article.   An update with additional detail can be found in Appendix A4.7 of the MBIE guidance document

However, changing the rules was only part of the story, as the industry then needed to get up to speed with the new Ductile Mesh,  interpretation of the rules, and a new testing & compliance approach. Some in the industry struggled more than others. This generated a level of scrutiny by Government agencies and the media.

Regulatory, Standards, and Compliance Framework

Residential building mesh manufactured & supplied in NZ sits within a multi-tiered regulatory framework that is designed to ensure buildings are of an acceptable quality.


This framework is designed to ensure owners and occupiers of buildings are provided with buildings that are safe, are of an acceptable quality, and contribute to peoples’ wellbeing from a social, health & sustainability perspective.  Furthermore, it ensures appropriate checks and balances are in place for those responsible for designing, building, regulating & overseeing construction.  As shown in the figure above, the framework consists of:

  • The Building Act, which sets out the rules for building in NZ.  It includes the need for buildings to comply with the Building Code; the licencing & disciplining of those performing building work; and the accreditation, duties & powers of organisations responsible for overseeing building activities & products. 

  • The Building Code, which sets out the performance standards for building in NZ.  It describes how buildings must perform but not how to achieve the level of performance.  It is designed to ensure an acceptable quality during the building process.  It is divided into eight sections sections, A-H, which cover different aspects of the structure.  Even buildings that do not require consent must meet the building code

  • Two routes to achieve Building Code Compliant Solutions for each section of the code. The first route is to follow one of the approved solution or verification methods published by MBIE, and the second is to employ an alternative solution, which for example, could be an engineered design with its associated calculations. The second route is often used for more complex projects.

  • Solution standards, which are used in their entirety, with any MBIE specified modifications, to specify an acceptable solution.  They describe an acceptable design.  For example NZS 3604 shows how to construct all aspects of a timber framed building.  NZS 4229 does the same for Masonry structures.

  • Verification standards, which describe design methods.  For example NZS3603 is the design standard for timber structures and provides much of the engineering basis for NZS 3604.  NZS 4230 does the same for Masonry structures.

  • Product standards – standards defining aspects such as the performance, verification & compliance of product used in a solution.  For example NZS 3622 in the area of timber strength & stiffness, and NZS 4671 in the area of Reinforcing material.

Industry quality accreditations, are processes by which an organisation's manufacturing and product quality verification competency are certified.  Examples are ISO9001 and ACRS (Australasian Certification Authority for Reinforcing and Structural Steels) accreditation  


So in the case of mesh, within a residential building, examples of relevant areas within the framework, and relevant standards, include:

  • Building Code section B1, which covers the structural stability of buildings 

  • The MBIE B1 accepted solution & verification method document, lists the standards, and modifications to those standards, required to meet the building code. For example, it specifies that NZS3604 is an acceptable solution method for timber-framed buildings, up to a maximum of three stories, on “good-ground”

  • NZS 3604 Chapters 6 & 7 provides foundation designs and concrete slab on ground floor designs.  It is important to note that sections 3.1.8 & 3.1.9 of the B1 accepted solutions document, heavily modifies the requirements of NZS3604 with regards to acceptable slab design and mesh requirements.  Specifically:
  • Unreinforced or fibre reinforced slabs are no-longer compliant
  • All reinforcing steel, including welded mesh, shall be ductility class E in accordance with NZS 4671
  • Reinforcing shall consist of a minimum 2.27 kg/m2 welded ductile reinforcing mesh sheets (1.14 kg/m2 in each direction)
  • Lapping requirements are specified

  • NZS 4671 is a product standard covering the performance, labelling, verification & compliance of steel used in reinforcing. i.e. bar & mesh.  However, again this standard is modified by the MBIE guidance in Chapter 14 of the B1 accepted solutions document, particularly with regards to testing, verification & lab accreditation. 

  • Laboratories that provide testing and certification of Grade 500E welded steel mesh for use in New Zealand must be accredited for testing to ISO 17025.  The accreditation agency must be a signatory to the International Laboratory Accreditation Cooperation (ILAC) Mutual Recognition Arrangement (MRA). International Accreditation New Zealand (IANZ) is a signatory to the ILAC MRA.

The above provides an overview of the regulatory framework and relevant standards, however the most current versions of the documents should be obtained and professional advice sought where required. 

Understanding the Mesh naming code - What does SE82DE mean?

NZ4671 describes the naming convention for welded mesh, where the:

  • Configuration of the bars is described by S (Square) or R (Rectangular)

  • Ductility Class is defined by L (Low), N (Normal) or E (Seismic) – as indicated above all reinforcing, including welded mesh, must be ductility class E if it is to provide an acceptable solution under the building code.

  • Size of the bar/wire is given in terms of its nominal bar diameter in mm

  • Spacing of the bars, in mm, divided by 100

Round 500E grade bar is used to make ductile mesh. The bar is Round and not deformed, as working the bar to make it deformed would reduce its ductility, i.e. make it brittle.

The suffix DE, is added to signify Double Edge

Thus, SE82DE is Square Seismic welded mesh, made with 8mm wire, with a 200mm aperture, and a Double Edge. It is made from Round (i.e. smooth) Grade 500E bar.

United Steel Compliant Ductile Mesh – NZ Made with NZ wire

Testing, compliance and labelling are a big part of giving consumers in NZ confidence that supplied mesh meets the required standards.


 All ductile reinforcing mesh manufactured by United Steel is made using bar/wire manufactured by Pacific Steel in Auckland, including the 500E bar used in our seismic mesh.  The 500E bar used in the mesh has bar markings, as shown in the following picture and on the Pacific Steel Website 


Our mesh manufacturing processes sit within our ISO9001 certified quality management system.  As shown here, this system & associated processes, ensures you are supplied mesh you can TRUST.  It does this by:

The Australasian Certification Authority for Reinforcing and Structural Steels (ACRS) evaluates the product quality and manufacturing processes of steel manufacturers, as it relates to the relevant standards. As such, steel purchasers can have confidence in the quality of steel from ACRS accredited manufacturers.


The structural integrity of the slab once in place, will in part be influenced by the sheet lapping.  Lapping requirements are defined in:

  • The MBIE B1 accepted solution & verification method document

  • NZS3101, which describes design practices for concrete structures

United Steel has used NZS3101 as the basis for its mesh lapping calculations & recommendations.  United Steel has on its website a list of all its available Ductile mesh and key specifications.  By selecting a mesh type (e.g. SE62) you can click through to a webpage with lapping diagrams for that type of mesh.  United Steel Mesh and lapping specifications are also available for download in our reinforcing handbook

To order reinforcing and mesh you can trust please email chch.sales@unitedsteel.co.nz or call 0800 800 649.  Please also contact us with any mesh enquires. 

For more information about how we can bring added value to your project, contact our specialists on 0800 800 649

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