CoWs and collaboration

By - , Build 182

In Build 180, we covered the basics of certificates of work (CoWs). Here, we go into more detail about how to include multiple contributors in your documentation.


DESIGN CAN BE a collaborative process, especially on more challenging projects. Sometimes, a piece of speciality design will be included in your overall design. Whether you have a complex foundation designed by a civil engineer or have included prefabricated timber trusses, if another designer has designed restricted building work (RBW), it will need to be included in CoW documentation.

Who can issue a CoW?

Professionals who are licensed or registered to be able to design RBW can provide a CoW for that work. This includes:

  • licensed building practitioners with a design licence
  • registered architects
  • chartered professional engineers.

Under current regulation, chartered professional engineers (under the Chartered Professional Engineers of New Zealand Act 2002) and registered architects (under the Registered Architects Act 2005) are automatically treated as LBPs licensed in the design class area of practice 3. Registered architects and chartered professional engineers have their own registration bodies that manage their registration and oversee their professional conduct.

Collaborative design

Where two or more LBPs or other suitably registered professionals carry out or supervise the design work for a building consent application involving RBW, there may be a choice about who provides the CoW.

If a particular design is both carried out and supervised by LBPs licensed in design, the CoW could be provided by either the LBP that carried out the design work or the one that supervised it.

However, if two designers work on different aspects of the plans and specifications that are RBW, each designer would be expected to provide a CoW for their respective parts. For example, one may have designed the foundation and the other designed elements of the superstructure.

You are taking responsibility

Producing and signing a CoW means a designer is providing a statutory undertaking certifying that the design documents are compliant with the Building Code.

You can provide a CoW that covers other LBP designers’ work, but it is important to be aware that, in this situation, the one who signs the CoW is taking responsibility via that certification statement. You may be signing off someone else’s work saying that it complies with the Building Code, so you need to do your due diligence on that work.

Including producer statements

A producer statement is a document prepared by a chartered professional engineer confirming their professional opinion. This opinion is based on stated reasonable grounds that aspects of design of a building achieve compliance with the Building Code or that elements of construction have been completed in accordance with the approved building consent.

The producer statement contains the name of the engineer and their firm. It signals to the building consent authority that certain design and monitoring work has been done – or overseen/supervised – by a practitioner who is competent to perform the defined work. However, a producer statement is not a product warranty or guarantee of compliance. It is a professional opinion based on sound engineering judgement.

An LBP may reference a producer statement in a CoW when an engineered element has been used in a design. An example of this could be when factory-designed and built trusses are incorporated in a design. The LBP would specify the truss and ensure it was fit for purpose in the overall design. However, the detailed design was carried out by the truss producer, so the producer statement could be referred to in the CoW for that section of the design.

Where a producer statement has been used to support the demonstration of Building Code compliance, it should be cited in the reference column of the CoW, along with other relevant specifications and reports – a geotechnical engineering report.

Further guidance

For further advice, see Guidance on the use of certificates of work, producer statements, and design features reports. This document was developed for the Canterbury rebuild but the principles apply for design RBW anywhere in New Zealand.

More information about producer statements can be found on the engineering New Zealand website



1. Who can design RBW?
a. Design LBPs.
b. Registered architects.
c. Chartered professional engineers.
d. All of the above.

2. If a chartered professional engineer designed some of the RBW on a project, it can be documented by:
a. Referencing a producer statement from the engineer in your CoW if the engineered element is used in your design.
b. A separate CoW provided by the CPEng.
c. It does not need to be documented which CPEng completed the design of the RBW.
d. a and/or b may be appropriate, depending on the situation.

3. You are using prefabricated trusses in your design. The trusses were designed in the factory. How do you include this restricted design work in a CoW?
a. By referencing a producer statement from the truss manufacturer in your CoW and showing how you have incorporated the trusses in your design.
b. The factory must produce a CoW for every site project where their trusses are used.
c. You don’t need to reference the trusses at all in your CoW.

Answers: 1. d,  2. d,  3. a

Download the PDF

More articles about these topics

Articles are correct at the time of publication but may have since become outdated.