External wall cladding system vertical fire spread - risk assessment approach

Provides a risk assessment approach to determine fire testing options for external wall cladding systems for vertical fire spread based on building height and risk group.

A simplified risk assessment approach has been developed to classify a building’s level of complexity and fire risk to help identify suitable fire test protocols to assess the cladding system for external vertical spread of fire. The parameters considered are:

  • building height
  • vulnerability of risk group
  • provision of an automatic fire sprinkler system to the requirements of NZS 4541 (as modified by the NZBC).

How to use this table – find the risk level Low, Medium or High applying to the building based on the building height and risk group. Refer to the table key to determine the fire testing options considered acceptable for the applicable risk level.

Table 1: External wall cladding system - risk matrix for fire testing protocols

Building height Sleeping use*
Risk groups SM, SI
Non-sleeping use*
Risk groups CA, WB, WS, VP 
Sprinkler
protected
Non-sprinkler
protected
Sprinkler
protected
Non-sprinkler
protected
Single level Low Low Low Low
≤ 10 m and
up to 2 levels
Low Low Low Low
> 10 m and ≤ 25 m Medium † High Medium Medium
> 25 m and ≤ 60 m High n/a Medium n/a
 > 60 m  High  n/a  High  n/a

* For building height ≤ 10m, cladding systems used for important level four buildings or multi-floor buildings incorporating staged evacuation, phased evacuation or evacuation to a place of relative safety within the building should meet the requirements for risk levels Medium or High given below.

† Where a NZ 4515 residential sprinkler system is installed then the non-sprinkler risk level in column 3 should be used instead (i.e. risk level High given below)

Where risk levels Low, Medium and High are matched to fire testing protocols P1 to P5 as follows:

Low

No requirement for building height ≤ 10 m (NZ Building Code Performance Clause C3.5).

Medium

  • P1. All cladding and rigid air barriers used in the external wall construction may be individually tested using ISO 5660-1 to meet requirements in C/AS2 to C/AS7 Paragraph 5.8. Insulation products, and filler materials (not including gaskets, sealants etc) to be limited combustibility*. Timber framing and combustible battens may be permitted in buildings with a building height of up to 25m, and must be properly encapsulated and/or protected (see P5) in buildings with a building height over 25m. All external wall cavities need to be fire stopped using cavity barriers at each floor level and at the junctions to other vertical fire separations. ACP materials must be tested without Aluminium (metal) facing as per C/AS2 to C/AS7 Appendix C7.1.5.

Any of options P2-P5 below are also acceptable.

High

  • P2. External wall cladding system may meet the performance criteria given in BR 135 for cladding systems using full scale test data from BS 8414-1:2002 or BS 8414-2: 2005; or
  • P3. External wall cladding system may pass the NPFA 285 full scale test; or
  • P4. External wall cladding system may meet ‘EW’ classification in AS 5113; or 
  • P5. All cladding, framing**, battens, insulation products**, rigid air barriers and filler materials (not including gaskets, sealants etc) used in the external wall construction may be of limited combustibility*. If vapour barriers, drainage mats, building wraps or similar are not of limited combustibility* then all external wall cavities need to be fire stopped using cavity fire barriers at each floor level.

* Limited combustibility means the product/material meets one or more of the following criteria:

  1. A1 or A2 classification in accordance with EN 13501-1:2007+A1:2009.
  2. Non-combustible or not combustible when tested to AS 1530.1 or ISO 1182.
  3. Concrete, brick/block masonry, stone, glass, ceramic tiles, aluminium and steel with or without paint or similar thin surface coatings not exceeding 1 mm thickness.

** Timber framing (or combustible insulation products within a framed wall assembly) may be used if a robust protective lining material (being of limited combustibility) is fixed to the exterior side of the framing and can be demonstrated to remain in place and protect the framing during the period of external fire exposure. 'Protect framing' can be assumed to be achieved if the protective lining material as part of a light timber frame wall exposed to the test conditions of AS 1530.4 can be shown to prevent charring of the timber frame for a period of 30 minutes. One way to determine this is to limit the temperature on the cavity side of the fire-exposed protective lining material during the test period to be no greater than 300 degrees Celsius.

Use of combustible rigid air barrier

A combustible rigid air barrier, for example plywood, may be used for any building if it has been included as part of a representative external wall subjected to a full scale fire test and meeting the criteria in P2-P4 in the risk matrix.

External walls of any height located within 1 m of a relevant boundary

To limit potential horizontal fire spread to and from a neighbouring property, the exterior cladding material shall either be of limited combustibility or be tested using ISO 5660-1 to meet the requirements in C/AS2 to C/AS7 Paragraph 5.8. The test specimen shall comprise the cladding material mounted over a representative substrate if the cladding material is less than 50 mm thick.

NOTE: This is not a vertical fire spread provision and needs to be considered in addition to the requirements of Table 1.

It is also acceptable for the exterior cladding material to be tested using ISO 5660-1 using an external irradiance of 30 kW/m2 and not ignite within the period of time given in NZBC C3.7.

Technical assessment in place of test

Cladding products and systems range in nature and complexity. There are also a range of base wall assemblies that may impact upon how the outer weather-facing part of a cladding system product will perform. Examples include:

  • Exterior Insulation Finish Systems (EIFS)
  • High Pressure Laminates (HPL)
  • external thermal insulation composite systems (ETICS)
  • rain screen cladding
  • structural insulation panel systems (SIPS)
  • Expanded Polystyrene Systems (EPS)
  • timber cladding.

Key system performance considerations that must be considered in a technical assessment are:

  • combustibility of insulation
  • combustibility of framing (e.g. timber frame)
  • composition of rigid air barrier
  • building underlay
  • uninterrupted vertical cavity
  • continuity of products.

In order for an external wall cladding system to be certified for fire safety performance, it needs to be constructed to replicate the details of the test. This includes, for example, framings, substrate, flashing details, gaskets, sealants and fixing mechanisms.

A technical assessment may be presented as part of the plans and specifications to demonstrate compliance with the performance requirements of the Building Code. Situations may arise where the proposed cladding system installation differs slightly from the absolute details of that described in a fire test report. A technical assessment must be provided by accredited testing laboratory or from a subject matter expert with knowledge and experience in fire science and fire testing.

This information is published by the Ministry of Business, Innovation and Employment’s Chief Executive. It is a general guide only and, if used, does not relieve any person of the obligation to consider any matter to which the information relates according to the circumstances of the particular case. Expert advice may be required in specific circumstances. Where this information relates to assisting people: