Group Numbers are required for surface finishes in certain areas of some buildings.
Group numbers, also known as fire ratings, are a numerical representation using a scale rating of a reaction to fire of a surface finish. The group number represents the rate at which a fire spreads across the surface.
Group Numbers are sometimes referred to as a fire resistance rating.
In the construction industry a surface finish is defined in the NZBC Handbook as the combination of a surface coating and the substrate material for visible building elements. It could be a decorative or protective coating that has been applied, a surface laminate, veneer, another material, or the uncoated building element itself.
Our timber veneer and wall panelling products all fall within the definition of a surface finish when used as a wall or ceiling panel.
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What is Clause 3 or C3?
Clause C requires design and construction for a low probability of injury or illness to people not in close proximity to a fire source.
It ensures there is fire protection for upper floors and building occupants from external vertical fire spread and protecting property nearby. It includes requirements for all buildings against fire spread to other property vertically or horizontally across a relevant boundary.
Clause 3 is also in place to help facilitate firefighting and rescue operations.
Verification Method
Tests or calculation methods that prescribe how to comply with the Building Code.
The Verification Method C/VM2, Framework for Fire Safety Design, provides a means of compliance with the New Zealand Building Code Clause C3 Protection from Fire. It is issued under section 22 of the Building Act 2004 as a Verification Method. This Verification Method is one way that can be used to show compliance with the New Zealand Building Code Clause C3 Protection from Fire. This Verification Method has been in effect since 5 November 2020.
Acceptable Solution
Simple step-by-step instructions that show one way of complying with the Building Code.
Alternative Solution
Is a building solution that differs, partially or completely, from the other options offered in the Acceptable Solution or Verification Method but achieves compliance with the performance requirements of the Building Code.
A design that complies with an Acceptable Solution or Verification Method must be accepted by a Building Consent Authority (BCA) as complying with the Building Code.
For many building projects, especially complex ones, the generic requirements of the Acceptable Solutions and Verification Methods documents often do not fit. These types of projects will need to follow an alternative solution for fire safety design.
Any Alternative Solutions will require detailed supporting documentation and will need to go through a building consent process with a BCA.
Group Numbers for VidaSpace Products are supported by Verification Methods and Acceptable Solutions.
Fire rating Group Numbers are a scaled rating system between 1 and 4. these numbers represent the measured time to ‘flashover’. The fire test procedure for establishing the Group Number is based on either:
The Group Number 1-4 (least to most combustible) provides a hierarchy for the risk of the spread of flame across the surface finish based on the measured or predicted ‘time to flashover’ in the ISO 9705 test.
The “S” suffix on Groups 1 and 2 indicates a lower smoke growth rate, so can be used in buildings or areas not protected by a sprinkler system.
Australia and Europe use the same general hierarchy of risk for surface flame spread for finishes. While differences exist in the small-scale or intermediate-scale fire test methods, the resulting classifications are considered to be sufficiently similar to the Group Number requirements. Meaning the results can be used directly for the purpose of compliance with Clause C3.4 of the NZBC.
Based on use and occupancy, risk group, and building importance level, different areas within buildings will require different Group Numbers. Over-specification is acceptable. Below is some of the possible applications for our products, as well as the permitted group number(s).
Wall/ceiling materials in sleeping areas where care or detention is provided:
Wall/ceiling materials in exit ways:
Wall/ceiling materials in all occupied spaces in Importance Level 4 buildings:
Ceiling materials in crowd and sleeping areas. Excludes where care and detention is provided and household units:
Wall materials in crowd and sleeping areas. Excludes where care and detention is provided and household units:
Wall/ceiling materials in occupied spaces in all other locations in buildings including household units:
New Zealand uses the following tests to determine the group numbers for building materials:
ISO 9705:1993 ‘Fire tests – The full-scale room test for surface products’.
This test method is used for establishing the Group Numbers for building materials.
In Australia, the Group Numbers are derived from AS ISO 9705:2003 which is an identical reproduction of ISO 9705:1993.
In Europe, the reaction to fire, of construction products and materials is classified using the criteria and test methods described in EN 13501-1:2007+A1:2009. The classification levels are A1, A2, B, C, D, E and F, from least to most combustible.
ISO 5660-1:2015 ‘Reaction-to-fire tests. – Heat release, smoke production and mass loss rate – Part 1: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement). The heat release rate results from this test are used to predict the likely time to flashover in the full-scale ISO 9705 room test.
Some products, especially those from Australia, may have been tested to AS/NZS 3837. This is the same test as ISO 5660 but with different end-of-test criteria, which means for some materials this may affect the assessment of a Group Number.
In Europe, the reaction to fire, of construction products and materials is classified using the criteria and test methods described in EN 13501-1:2007+A1:2009. The classification levels are A1, A2, B, C, D, E and F, from least to most combustible.
The Single Burning Item (SBI) as described in EN 13501-1:2007+A1:2009 is a test method for determining the reaction to fire behaviour of building products when exposed to the thermal attack by a propane burner. The results of this test, using a Fire Growth Rate (FIGRA ratio) have been correlated for MBIE to the ISO 9705 Group Numbers and the requirements of NZBC Clause 3.4(a) in the same manner as the ISO 5660 cone calorimeter test.
The co-relation of wall and ceiling surface finishes derived from Australian or European classifications to New Zealand fire ratings can, without the need for further testing, be taken as described in the following table.
Ever spent a lot of time making a wall finish selection for your design only to have to change it because it doesn’t meet NZBC fire rating requirements for the space?
To achieve a higher fire rating than Group 3 for timber, the products will need to be treated or lined with fire-retardant materials such as an intumescent coating. There are few solutions available with some being more cost-effective. With the choice of clear or pigmented fire protection coatings for wood products to help achieve a Group Number of 1-S. This effectively means that the timber product can be used in any area of a building’s interior.
What is intumescent coating?
Intumescent coating is a layer of protective substance that works by chemical reaction generated by heat, resulting in swelling and formation of an insulating layer on the surface, with or without the release of water. This type of coating provides a cost-effective as well as a practical solution for fire protection and corrosion protection of structures made of alloys and steel [and wood], and can also be used in a decorative capacity.
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Please note that this advice is prepared as a guide only. Always seek professional advice from a registered Fire Engineer and refer to the Building Code for detailed requirements.
Contact us at hello@vidaspace.co.nz 0r 0800 119 388 if you have any questions about fire ratings that we haven’t covered.
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