Fire test methods for external wall cladding systems

Clarifies what test methods can/may be used to determine fire performance of external cladding systems to demonstrate compliance with Building Code.

Fire testing requirements for an external wall cladding system

To demonstrate compliance with the Building Code for Protection from Fire Performance Clauses C3.5 and C3.7 for external vertical fire spread, the external wall cladding system includes all substantive components within the complete wall assembly. This includes sheet cladding materials, framing, rigid air barrier, any insulation, sheet materials or blanket and the internal lining. Where relevant, the direction of fire exposure to be considered is from the exterior side of the wall.

Recommendations on the different fire testing options to evaluate the fire properties of an external wall cladding system are given in the risk matrix in "External wall cladding system vertical fire spread – risk assessment approach".

Alternative test methods to those currently cited

The New Zealand Building Code Protection from Fire Acceptable Solutions and Verification Method currently cite two fire tests for assessing the fire performance of cladding systems. These are a bench scale independent component test (ISO 5660), and the intermediate scale system test NFPA 285. This guidance broadens the suite of test protocols to include the British Standard BS 8414 with the acceptance criteria provided by BR 135.

  • BS 8414-1:2015 Fire performance of external cladding systems. Test method for non-loadbearing external cladding systems applied to the masonry face of a building. Amended by BS 8414-1:2015+A1:2017 (June 2017).
  • BS 8414-2:2015 Fire performance of external cladding systems. Test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame. Amended by BS 8414-2:2015+A1:2017 (June 2017).
  • BR 135 Fire performance of external thermal insulation for walls of multi-storey buildings: (BR 135) Third edition, BRE (15 March 2013).

It is also acceptable to test cladding systems using the methods outlined in the Australian Standard AS 5113 to meet the ‘EW’ (external wall) classification. This classification standard in turn references BS 8414 as a test method.

Test components within cladding systems can also be tested using the methods outlined in EN 13501: 2007+A1:2009 to meet a Euroclass A1 or A2 classification.

For guidance on where the different test methods may be used, refer to the risk matrix in the "External wall cladding system vertical fire spread – risk assessment approach".

BR 135 Fire performance of external thermal insulation for walls of multi-storey buildings – 3rd edition 2013

BR 135: 2013 addresses the principles and design methodologies related to the fire spread performance characteristics of non-loadbearing external wall cladding systems. Although various potential design solutions have been identified and discussed in BR 135, robust design details are not presented. In this rapidly changing market generic solutions are not available where new products and novel design solutions are frequently presented. The illustrations and scenarios presented in BR 135 are based on typical examples of current practice in the UK. To help designers and end users better understand the parameters impacting on the fire-safe design and construction of external wall cladding systems, BR 135 focuses on the issues surrounding the topic of external vertical fire spread.

BR 135 Annex A provides a classification system for the test methodology outlined in BS 8414-1 Fire performance of external cladding systems – Part 1: Test method for non-loadbearing external cladding systems applied to the face of the building.

BR 135 Annex B provides a classification system for the test methodology outlined in BS 8414-2 Fire performance of external cladding systems – Part 2: Test method for non-loadbearing external cladding systems fixed to and supported by a structural steel frame.

Other construction systems such as concrete-framed or timber-framed construction are not considered in BR 135. However, the general principles in the BR 135 guide may still apply, although suitable additional risk assessments and detail design reviews would be required. The risk matrix approach provides an option for considering alternative forms of supporting wall frames.

What is specifically excluded from external wall cladding systems for compliance with C3.5 and C3.7?

For the purposes of an external wall cladding system as defined in Section 4.1 of this guidance and for demonstrating compliance with the Building Code for Protection from Fire, substantive components may exclude:

  • signage and billboards – aggregated area up to 25 m2
  • video screens up to 6 m2
  • greenwalls – the acceptance of green and living walls will be dependent on the type of system proposed, its support structure and the associated management and maintenance/irrigation procedures. Generally, plants growing on metallic support systems (such as stainless steel wires) will not present an increased fire hazard provided they are adequately maintained. Other systems that include combustible support systems should be proven via fire test evidence to support compliance. For more information on greenwalls refer to:

    ANS Living Walls receive a Fire Safety Standard on the ANS global website

    Fire Performance of Green Roofs and Walls on the GOV.UK website
  • sunscreens/sunshades/louvres up to 6 m2 or any area if non-combustible
  • any materials used as part of the external wall cladding system for the topmost floor provided the roof does not require a fire resistance rating. (Other requirements to prevent horizontal fire spread to other property may still apply e.g. limits on unprotected area and/or the ignitability of the wall cladding when located within 1 m of the relevant boundary .)
  • doorsets and window frames (these are not included with the cladding requirements)
  • sealants and tapes comprising < 5% of the wall area
  • a canopy or balcony at ground floor level of buildings that exceed 10 m in height where it can be shown or is agreed that a fire is unlikely to spread from the area to the main external wall cladding
  • minor trim and gutters, downpipes and fascias – limited amounts of materials are excluded from the requirements where it can be shown or is agreed that a fire involving the materials is unlikely to spread fire to the remaining parts of the external wall cladding or where they are remote from the main building cladding.
  • individual components on or within the wall assembly that are non-combustible but include a surface coating not more than 1 mm thick.

Note: the above exclusions are only relevant to each component when taken in isolation. Consideration needs to be given when the above items are combined as part of a whole system to determine the contribution of each component to the overall performance of the cladding system. For example, a video screen meeting the size limitations attached to a noncombustible cladding would require further consideration and might not be appropriate if attached to a combustible sunscreen or rainscreen system.

In-wall cavities

Continuous vertical channels and cavities within external wall cladding systems are known to promote upward vertical fire spread. Fire researchers have noted that when flames are confined within a vertical cavity or channel they elongate, leading to flame extension of up to five to ten times the expected unconfined flame lengths. This is true even in cavities without additional combustible materials present, but is made worse by the presence of combustible materials. This flame extension effect can support rapid, potentially unseen, fire spread within an external wall cladding system and must be limited.

The provision of cavity barriers within external wall cladding systems is important, particularly when combustible cladding, rigid air barriers and insulation products are used.

Cavity barriers based on fire-resisting construction tested to AS 1530.4 or similar and satisfying integrity and insulation ratings for at least 30 minutes are likely to provide an acceptable means of controlling flame spread within cavities. However, additional consideration is needed to ensure that cavity barriers within a facade system located at the junction of fire separations and the external wall assembly have adequate support, can remain in place for the period required, and provide the required level of fire resistance rating.

Examples of other potentially acceptable test standards that may be used for curtain wall systems include:

  • ANSI/ASTM E2307 Standard Test Method for Determining Fire Resistance of Perimeter Fire Barriers Using Intermediate-Scale, Multi-story Test Apparatus, or
  • BS EN 1364-4:2014 Fire resistance tests for non-loadbearing elements.

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: