Fire testing of cladding.
Fire testing protocols: individual components versus cladding systems
Historically, fire testing protocols used for Building Code compliance in New Zealand have been based on either bench scale testing of individual materials or components using AS/NZS 3837 (or more recently ISO 5660) or the larger scale NFPA 285 facade test.
Bench scale fire tests have typically been used in New Zealand for cladding in a way that treats fire spread over the external wall as a surface flame spread phenomena (similar to interior linings). However, it is apparent that in many cases it is the entire system performance that must be considered and not only that of the outermost cladding material.
Large scale fire tests are a way of assessing how an external wall cladding system performs when exposed to flames projecting from an opening in the external wall. Fire performance in these tests can be sensitive to a small change in the system details. External wall cladding systems are complex and can include a multitude of combustible components. It is difficult to determine how each of those individual components contributes to the overall system performance to limit fire spread.
It may therefore not always be possible to confidently evaluate the overall system performance for facades containing combustible components solely based on small scale fire testing of only the individual components.
Purpose of this guidance
This document has been prepared to provide guidance:
- On how the fire test criteria should be applied to external wall cladding systems.
- To support the industry stakeholders in determining NZBC compliance for external wall cladding systems.
Scope of this guidance
This guidance is intended to:
- make it clear what constitutes an external wall cladding system for testing external vertical fire spread and assessing performance against the New Zealand Building Code requirements
- describe the suite of fire testing protocols that could be applied to demonstrate compliance with the Building Code
- scope the parameters that need to be considered when addressing external vertical fire spread.
The guidance does not intend to provide a fire-engineered design solution for individual construction details but covers broad principles requiring consideration in their development.