A White Paper on the NZ Building Code B2 (Durability) - Opus
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A White Paper on the NZ Building
Code B2 (Durability)
Issues, Solutions and where to from here
Prepared by Raed El Sarraf, Corrosion & Asset Integrity Consultant, WSP Opus
Abstract
The New Zealand Building Code (NZBC) sets the performance standards that all structures are
required to comply with. Its main purpose is to ensure they are safe, healthy and durable for
everyone who may use them. While Clause B2 applies to all aspects of a building, from
foundations to pipework and electrical cables, this paper addresses B2 as it applies to a primary,
load-bearing structure. The guidance given in the B1 Structures clause is clear on how
engineers, and users, can both work toward its compliance (which includes a rigorous peer
review process) and demonstrate how compliance can be achieved. Unfortunately, it appears
that there are limitations with the B2 Durability clause of the NZBC, which has led to
misunderstandings on achieving and demonstrating compliance, especially regarding
Acceptable Solution’s or using the Verification Methods for some common construction
materials.
This is especially an issue when Councils are requesting Producer Statements that are signed
covering B2, but how can Engineers and Architects sign them if the means of achieving
compliance is not clear?
This white paper highlights the issues and challenges being experienced by Design Engineers
and Architects, in meeting the expectations or requirements of Building Control Authorities
(BCA). This is then followed by a proposed pathway to addressing these issues, with the aim of
demonstrating compliance with the B2 Clause of the NZBC.
Introduction
The New Zealand Building Code sets the performance standards and means of compliance for
all structures that are covered by the Building Act. While this is commonly taken as being
buildings and houses, it also includes road and rail bridges, other types of infrastructure
including lighting poles and even house fences. The main purpose of the Building Code is to
ensure buildings are safe, healthy and durable for everyone who may use them.
The guidance given in the B1 Structures clause is clear on how engineers, and users, can work
toward its compliance (which includes a rigorous peer review process). Unfortunately, it appears
that the B2 Durability clause of the NZ Building Code (current edition dated 1 January 2017) has
some limitations; especially with regards to the use of structural steel and other metals (such as
aluminium, stainless steel, etc).
There are two main requirements that all structures need to meet to ensure compliance with
this part of the Building Code, these are:
• Clause B2.2; Functional Requirement
Building materials, components and construction methods shall be sufficiently durable
to ensure that the building, without reconstruction or major renovation, satisfies the
other functional requirements of this code throughout the life of the building.
Version 1.0 Dated 4/07/18
Released: 5/07/18• Clause B2.3.1; Performance
Building elements must, with only normal maintenance, continue to satisfy the
performance requirements of this code for the lesser of the specified intended life of the
building, if stated, or…
This is then followed by guidance on the period that the different building elements should be
designed for, which is typically taken as 5, 15 or 50 years. It should be noted that bridges are
typically taken as having an intended life of 100 years.
While the above requirements are clearly stated, the guidance for using structural steel and
other metals is limited. For example:
• There are no references to the relevant structural steel, other metals and protective
coatings related durability standards within B2.
• There are no Acceptable Solutions for structural steel structures, the use of protective
coatings and/or recommended detailing.
Having said that, it is given that to satisfy the Building Code, all building elements should satisfy
with what is known as the “Verification method B2/VM1”. However, currently this is open to
interpretation and there is no guidance on how any organisations and/or practitioners become
qualified to undertake steelwork (and metals) durability design.
A Conundrum: Producer Statements and How to Demonstrate Compliance?
Upon the completion of the design of a structure, such as a structural design to the B1 Structure
Clause of the NZBC, two Producer Statements (PS) are required being:
• PS1 Design
• PS2 Design Review
These documents are required to be signed by a suitably competent and qualified person. For
example, upon the completion of a structural design, a PS1 and PS2 are signed by a Chartered
Professional Engineer (CPEng) and/or suitably qualified practitioner on the BCA’s register. These
personnel have clearly demonstrated their competencies and experience to Engineers New
Zealand, thus are deemed to be suitability qualified in their area of practice. When accepted by
the Building Consent Authority, it can issue a Building Consent. Following construction, two
further Producer Statements, PS3 Construction and PS4 Construction Review, that confirm that
the design has been has been complied with are required, before a Code Compliance
Certificate is issued.
This is standard practice, with an accepted and clear pathway for engineers and architects to
demonstrate their competency (e.g. CPEng), and a way to demonstrate compliance through
the B1 Structure Clause.
However, what is the pathway to demonstrating both competency for durability design, and
compliance with B2 Durability?
Version 1.0 Dated 4/07/18
Released: 5/07/18At the time of writing, it is understood that discussions are being held between different
organisations about why practitioners are not signing off Producer Statements for durability,
and how to demonstrate compliance with the NZBC. This discussion is between the Auckland
Council, Christchurch City Council, and Ministry of Business Innovation and Enterprise (MBIE)
with Engineers New Zealand and the Association of Consulting Engineers NZ (ACENZ); where
the Councils are requesting evidence of compliance for B2 Durability by completion of
producer statements1.
Since 30 June 2017, instead of issuing a PS1, it has been recommended by Engineers New
Zealand and ACENZ for engineers to issue a letter with a given format, where it clearly states:
We are not able to provide a Producer Statement for durability because compliance needs to
be shown on a material-by-material basis using a variety of compliance methods, and not all
materials used have a clear compliance path.
It then concludes with listing the relevant document for the given material. Timber is
referenced back to an Acceptable Solution given in NZBC B2/AS1, concrete to NZS 3101, and
steel corrosion protection to AS/NZS 2312.
What this confirms is that a clearer pathway is required, not only from demonstrating
compliance with the B2 Durability Clause, but also for practitioners to demonstrate their
competency to be able to sign off producer statements.
Proposed Pathway and Solution
To address both the current limitations and the highlighted issues, the following proposed
pathway is given:
Review of the B2 Durability Clause
To address the lack of guidance regarding the corrosion protection of structural steel, the
review of the B2 Durability Clause should, as a minimum, include reference to:
• AS/NZS 2312 (all parts): which cover the requirements of the selection, specification,
application and inspection of different types of protective coatings.
• AS/NZS 5131: which provides additional guidance regarding the application and
inspection of protective coatings during fabrication; including guidance regarding
Architecturally Exposed Structural Steelwork (AESS). This document is now cited by MBIE
and will come into force from 3 July 2018.
• SNZ TS 3404: This technical specification provides the latest guidance for the corrosion
protection of structural steel in the NZ environment, for both atmospheric and non-
atmospheric environments. This document was published in February 2018.
Fortunately, both NZ Heavy Engineering Research Association (HERA) and Steel Construction
NZ (SCNZ) are currently in discussion with MBIE on the inclusion of the above Standards as
Acceptable Solutions into the B2 Durability Clause. It is envisioned that the latest version will be
issued later this year.
In addition to the above, it is recommended that a durability guide, detailing issues and
solutions for different materials (not just structural steel) is developed. These may also be
included as Acceptable Solutions in the B2 Durability Clause or published as a supplementary
document to the NZBC.
1
https://www.engineeringnz.org/news-insights/producer-statements/
Version 1.0 Dated 4/07/18
Released: 5/07/18Other documents that should be referenced under the Verification Method are:
• HERA Report R4-97 New Zealand Weathering Steel Guide for Bridges
• HERA Report R4-133 New Zealand Steelwork Corrosion and Coatings Guide
Finally, guidance with suitable references related to durable design in other metals, such as
stainless steel is also required.
Demonstrating Competency to sign off PS1 and PS2
We understand that currently there are only 2 chartered professional engineers with their
practice area related to the corrosion protection of structural steel. To address the current
limited number of chartered engineers in this field in New Zealand, who can sign producer
statements (PS1 and/or PS2), Section 8.2 of the New Zealand Transport Agency Protective
Coatings for Steel Bridges currently states:
Chartered Professional Engineers who sign a Producer Statement (PS2) confirming the
requirements of the B2 (Durability) Clause of the Building Code has been met, should also
confirm that the specifying and detailing requirements have been met.
It was deemed that to demonstrate competency, a qualified coating specifier should have, the
following qualifications:
• NACE Protective Coating Specialist; or,
• Australasian Corrosion Association (ACA) Technician or Technologist with successful
completion of the ACA’s Coating Selection and Specification Course and/or certified to
NACE Coating Inspection Program (CIP) Level 2.
Based on the above, it is recommended that a similar qualification requirement is considered
by Engineering New Zealand when a competency pathway is developed. Of course, this needs
to be associated with relevant tertiary and specialist training qualifications and industry
experience. Due to the diversity of pathways possible (either from an engineering or scientific
background), it is suggested that they be identified as Chartered Professional Durability
Practitioners.
Signing off PS3 and PS4
PS3 is related to completion of the building work, which in this case is mainly related to the
correct application and installation of the corrosion protection systems on steelwork. While PS4
is related to the construction monitoring of the building work, in this case verifying that the
specified systems were installed, usually by ensuring that the relevant quality assurance process
was followed.
For issuing of a PS3, the following minimum requirements are recommended:
• Coating applicators to work within an effective quality assurance system and employ
trained and experienced blaster/painters and supervisor/inspectors, and have well
maintained plant and facilities. Depending on the structures complexity (such as a bridge
or AESS steel) and site corrosivity (such as ≥C3(Medium)), to be aligned with the
requirements of AS/NZS 5131 and SNZ TS 3404, the painting applicator should be
accredited under the Australian Painting Contractor Certification Program (PCCP). This is
currently a requirement for NZTA bridge painting.
• Only coatings approved by an independent body such as the Australian Painting
Approval Scheme (APAS), the North East Protective Coating Committee (NEPCOAT) or
Norsk Sokkels Konkuranseposisjon (NORSOK) shall be used on critical structures in severe
environments (≥C3(Medium) to ISO 9223).
Version 1.0 Dated 4/07/18
Released: 5/07/18For issuing of a PS4, the following minimum requirements are recommended:
• The use of an inspector certified by the NACE Coating Inspector Program or a Protective
Coatings Inspector with a current Competence Certificate issued by the Certification
Board for Inspection Personnel NZ (CBIP). It is important that the inspector’s
independence from the physical works and coatings contractor is maintained. Again, this
will not be required for all projects, for example painting a home garage/shed a qualified
coating inspector is not required; however, when painting a stadium, it should be.
Once the inspectors report is issued, a chartered design engineer and/or a chartered
durability practitioner can then issue a PS4.
Other Materials
While the above pathway recommendations and reviewing of the NZBC are mainly related to
structural steel, a similar review and pathway may be required for other construction materials.
For example, most of the durability design requirements for concrete are clearly given in NZS
3101. However, for situations that are beyond those given in that Standard, a specific durability
design will be required. This should be undertaken by a competent concrete specialist;
however, we understand that there is not yet a pathway for such personnel to demonstrate
their competency in this specialist field.
A review of how material specialists can demonstrate their competency is recommended.
Potential Timeline
As discussed earlier, the revised B2 Durability Clause is expected to be released by the end of
2018. However, the other recommendations given above are expected to take longer
depending on the time required to develop the competency pathways, and contractors and
suppliers achieving the required accreditations and qualifications (such as PCCP and APAS).
It is envisioned that the development of the competency pathway with Engineering NZ, may
take up to a year. After which, the current experienced materials specialists and engineers
should attain the Chartered Professional Durability Practitioner status.
For new entrants to this field, it is expected to take them at least 5 years (post tertiary
qualification) before they can demonstrate competency. This is a similar timeframe to current
CPEng requirements for other engineering fields.
As for contractors and suppliers, this depends on the status of their current Quality Assurance
and Control systems. Their required accreditations may be achieved within a number of
months to a year.
In summary, while a revised version NZBC B2 Durability Clause is expected by the end of year; it
should be accepted by the relevant organisations that there will be an interim period before a
comprehensive compliance system is put in place. Cooperation, and patience, between the
different parties is required, and the sooner this work is started the better.
How will this work in practice?
While the above proposal outlines a compliance and competency pathway that may be used
for all types of structures, in practice it is not expected that a chartered durability practitioner
will be required to sign off a PS1/PS2 in all cases.
It is envisioned that for common structures (such as low to medium-rise buildings), typical
durability related matters will be addressed via the relevant material standard and B2
(Durability Clause) Acceptable Solutions. As such, design engineers who demonstrated
compliance with NZ Building Code in this manner, are not expected to require a chartered
durability practitioner to sign off PS1/PS2.
Version 1.0 Dated 4/07/18
Released: 5/07/18It is envisioned that this sign off will only be required, for situations that are beyond those given
in the material standard(s) and Acceptable Solutions, especially when using the Verification
Method.
Conclusion
It has been recognised by the engineering fraternity that that there is a lack of guidance on
demonstrating design compliance with the NZ Building Code B2 Durability Clause. This not
only relates to the B2 Durability Clause itself but also for practitioners to demonstrate their
competency and a pathway to becoming a Chartered Professional Durability Practitioner in
their chosen materials related practice area is required.
This paper outlines the issues and proposes a number of solution to address this matter. This
includes the following recommendations:
• Review NZ Building Code B2 Durability Clause and incorporate suitable standards and
references for the corrosion protection of structural steel. This is currently underway.
• Outline the minimum qualifications required for the practitioners to undertake the
durability design and peer review for the corrosion protection of structural steel; from
which design Producer Statements (PS1 and PS2) may be issued.
• Outlines the minimum requirements for coating applicators, coating inspectors and the
coating itself, from which construction Producer Statements (PS3 and PS4) may be
issued.
• A review of the pathways to achieving a Chartered Professional Durability Practitioner
qualification for material specialists and engineers, not just for structural steel but other
materials such as stainless steel and specialist concrete.
• While the revised B2 Durability Clause is expected by the end of 2018, further work is
required to develop and implement the recommended solutions and pathway.
Cooperation between the different parties is required to ensure the timely
implementation of a comprehensive compliance system.
References
• AS/NZS 2312; Guide to the protection of structural steel against atmospheric corrosion by
the use of protective coatings. Standards New Zealand. Wellington NZ. 2002/2018.
• AS/NZS 5131:2016; Structural steelwork – Fabrication and erection. Standards New
Zealand. Wellington NZ.
• El Sarraf, R and Clifton, G.C.; New Zealand Steelwork Corrosion and Coatings Guide. HERA
Report R4-133. HERA. Manukau, New Zealand. 2011
• Engineers New Zealand/ACENC Producer Statement Letter;
https://www.engineeringnz.org/news-insights/producer-statements/
• ISO 9223:2012; Corrosion of metals and alloys- Corrosivity of atmospheres- Classification,
determination and estimation. Geneva, Switzerland.
• Mandeno, W. and El Sarraf, R; Protective Coatings for Steel Bridges. New Zealand
Transport Agency. Wellington, New Zealand. April 2017.
• NZ Building Code B1 Structures; MBIE, Wellington, New Zealand. 3 April 2018.
• NZ Building Code B2 Durability; MBIE, Wellington, New Zealand. 1 January 2017.
• NZS 3101:2006; Concrete structures Standard. Standards New Zealand. Wellington NZ.
• SNZ TS 3404:2018; Durability requirements for steel structures and components.
Standards New Zealand. Wellington NZ.
• Zaki, R, and Clifton, G.C; New Zealand Weathering Steel Guide for Bridges. HERA Report
R4-97. HERA, Manukau, New Zealand. 2005
Version 1.0 Dated 4/07/18
Released: 5/07/18You can also read
