Fireshield’s Guide to Surface Finishes

Interior surface finishes play a vital role in preventing the rapid spread of fire in buildings, helping ensure occupant safety and compliance with fire codes.

In New Zealand, the Building Code sets specific requirements around using fire-resistant surface finishes in certain high-risk areas based on a rating system called Group Numbers.

This guide will explain what constitutes a surface finish, the Group Number rating scale, where these fire-rated finishes are mandated, and how Fireshield can assist in identifying code-compliant systems to protect people and property.

What is a Surface Finish?

A surface finish is the exposed, visible layer applied to building elements like walls and ceilings. This includes decorative coatings, laminates, veneers, or the exposed base material itself if left uncovered.

Group surface ratings are applied to these visible surfaces to slow the spread of flame across the finish material. In basic terms, it gives building occupants additional time to safely exit before a fire spreads. The higher the group surface rating, the longer the delay before reaching critical conditions like flashover.

Surface finishes with appropriate group ratings are primarily used in public gathering spaces and exit paths - anywhere occupants will be congregating or trying to evacuate.

This includes restaurants, hospitality spaces, hotel lobbies, corridors, and stairwells.

To regulate this fire risk, the New Zealand Building Code requires the use of surface finishes with specific fire resistance ratings, called Group Numbers, in certain areas of buildings.

Understanding Group Number Fire Ratings

Group Numbers rate how combustible a surface finish is and its resistance to the spread of flames during a fire. The rating system goes from 1 to 4:

Group 1S (best possible rating) – Does not flashover within 20 minutes and has a low smoke growth rate indicated by the 'S' suffix.
Group 1 – Does not achieve flashover within 20mins but has a higher smoke growth rate than G1S.
Group 2 – Burns to flashover in 10-20 minutes
Group 3 – Burns to flashover in 2-10 minutes
Group 4 (highest combustibility) – Flashover in under 2 minutes

Note: "Flashover" is when a fire becomes so intense that all exposed combustible surfaces spontaneously ignite. The higher the group number rating, the longer it takes before this critical point is reached, providing more evacuation time.

Where Are Group Numbers Required?

The Building Code mandates minimum Group Number ratings for different areas of buildings based on factors like:

Occupant density and escape routes (i.e. exit ways, public spaces)
Building importance level
If the area is sprinklered

As a general guideline:

Group 1 or 2 finishes are required in higher-risk, higher-occupancy spaces like restaurants, theatres, and lobbies as well as exit paths and stairwells.

Group 3 is more commonly permitted in lower-risk residential units.

But the code provides full details - over-specification is allowed but under-specifying fire resistance can lead to failed inspections.

Choose Fireshield

Fireshield frequently sees designs underestimate the fire rating requirements, only realising the need for code-compliant finishes late in the build process. This can lead to costly rework and delays.

Some surfaces may be exempt from requiring a Group Surface rating, at Fireshield, we have leading Fire engineers and Architectural Designers in-house and are available to provide advice and documentation for all projects. However, if you are unsure reach out to us.

We develop, test, and manufacture our own products, as well as supply products from other leading manufacturers around the globe and sell them locally. Aside from recoating if the surface becomes damaged, our coatings require no maintenance to provide lasting fire protection for the life of the building. The coating becomes an integrated part of the substrate material.

With our expertise and previous design backgrounds, we can identify issues, engineer solutions early on, and keep your project running smoothly.

Get in touch with us to discuss how we can work together on your next project.