Understanding Building Classifications and Their Impact on FRLs in Queensland

Why mixed-use buildings demand careful passive fire planning

In Queensland, building classification is not simply a planning label — it directly determines required Fire Resistance Levels (FRLs), fire separation, compartmentation, and passive fire protection obligations under the National Construction Code (NCC).

As developments increasingly combine residential, retail and assembly uses within the same structure — such as apartments above shops and gyms — compliance complexity increases significantly. When multiple classifications exist within one building, the interaction between them can substantially alter required FRLs and construction types.

This article explores how Class 2, Class 6 and Class 9b classifications interact under the NCC, with a Queensland-focused case study examining a residential building undergoing renovation to introduce retail tenancies and a gym.

Building Classifications Under the NCC (Queensland Context)

Queensland adopts the National Construction Code (NCC), which categorises buildings based on their use. The most common classifications for mixed-use residential developments include:

• Class 2 – Sole-occupancy units (SOU) each being a separate dwelling (e.g., apartments)

• Class 6 – Shops, cafes, restaurants, showrooms and similar retail/commercial spaces

• Class 9b - Recreational, sports and fitness facilities (gyms, yoga studios, etc),

Each classification carries different risk profiles and occupant characteristics, which directly influence required fire protection measures.

Importantly, where multiple classifications exist within one building, the NCC treats the building as having multiple classifications. Fire separation and FRLs must then be determined based on:

• The specific classes involved

• The building’s effective height and rise in storeys

• Type of construction (Type A, B or C)

• The required fire separation between different classifications

What is an FRL and Why Does It Matter?

A Fire Resistance Level (FRL) is expressed as three numbers (e.g., 120/120/120), representing the duration in minutes that a building element maintains:

1. Structural adequacy

2. Integrity

3. Insulation

FRLs apply to elements such as:

• Fire walls

• Floor slabs

• Columns and beams

• Fire-rated partitions

• Service penetrations

When classifications change or multiple classes exist in one building, the required FRL between compartments often increases.

The Challenge of Multiple Classifications in One Building

Mixed-use buildings are common across Queensland, particularly in urban centres such as Brisbane, the Gold Coast and regional hubs like Cairns and Townsville.

However, combining classifications introduces several compliance considerations:

1. Fire Separation Between Different Classes

The NCC requires fire-resisting construction between:

• Class 6 (retail) and Class 2 (residential)

• Class 9b (gym) and Class 2

• Class 6 and Class 9b

• Each classification and fire-isolated exits

Depending on rise in storeys and construction type, separation between these classes commonly requires 120/120/120 FRL construction for floors and walls.

This means that:

• Floor slabs between retail and apartments must be fire-rated.

• Walls between a gym and residential units must achieve compliant FRLs.

• Fire doors must be installed where required openings exist.

2. Impact on Type of Construction

Construction type (Type A, B or C under NCC Volume One) is influenced by:

• Building height

• Rise in storeys

• Building classification

The introduction of a Class 9b component may trigger a higher construction type requirement than a purely residential Class 2 building.

For example:

• A low-rise Class 2 building may have previously complied under Type C construction.

• Introducing Class 6 and Class 9b tenancies can trigger Type B or Type A construction requirements.

• Structural elements may therefore require higher FRLs than originally designed.

The most restrictive classification often governs the required fire-resisting construction of the storey in which it is located.

3. Services and Penetrations

Retail and gym fitouts typically introduce:

• Commercial kitchen exhaust systems

• Mechanical ventilation upgrades

• Additional hydraulic services

• Increased electrical infrastructure

• Penetrations for amenities and air conditioning

Each penetration through a fire-resisting element must maintain the required FRL in accordance with NCC Specification C and AS 4072.1.

Common compliance failures in mixed-use renovations include:

• Unsealed penetrations

• Non-tested fire collars

• Fire-rated walls not extending to slab soffit

• Lack of documentation for installed systems

Case Study: Class 2 Building Converted to Mixed Class 2, 6 and 9b (Queensland)

Scenario

An existing three-storey Class 2 apartment building in Queensland undergoes renovation involving:

• Conversion of the ground floor into two Class 6 tenancies (café and retail shop)

• Conversion of one Level 1 apartment into a small commercial gym (Class 9b)

The building now contains:

• Class 2 – Residential apartments

• Class 6 – Retail/café

• Class 9b – Gym

This significantly alters fire compliance obligations.

How This Affects FRLs and Passive Fire

1. Ground Floor (Class 6) to Residential Above (Class 2)

The floor slab separating the Class 6 tenancies from the apartments above must provide compliant fire separation.

In a typical three-storey configuration, this commonly requires:

• 120/120/120 FRL floor construction

• Fire protection to supporting beams and columns

• Fire-stopping of all penetrations

If the original slab was designed only for residential separation, upgrades may be required.

2. Class 9b Gym Within Residential Level

Converting an apartment into a gym changes the risk profile significantly:

• Increased occupant load

• Patrons unfamiliar with exits

• Electrical equipment load

• Open-plan internal layout

The gym must be fire separated from:

• Adjacent Class 2 sole-occupancy units

• Public corridors

• Fire-isolated exits

Walls originally designed as inter-tenancy separation between Class 2 units may not achieve the FRL required between Class 2 and Class 9b areas.

This can trigger:

• Upgrading wall systems

• Installing fire-rated doorsets

• Sealing existing penetrations

• Extending partitions to slab soffit

3. Dual Fire Separation at Level 1

The Level 1 slab now performs two separation functions:

• Separating Class 6 (below) from Class 9b (gym)

• Separating Class 9b (gym) from Class 2 apartments above

This increases the importance of:

• Structural FRL compliance

• Service penetration integrity

• Shaft and riser fire protection

4. Impact on Fire-Isolated Exits

Class 9b areas have stricter egress considerations due to higher occupant density.

This can affect:

• Required fire rating of corridors

• Protection of stairways

• Door hardware and fire door compliance

• Exit separation distances

Passive fire elements enclosing exits must maintain compliant FRLs across all classifications.

Queensland Regulatory Implications

Under the Building Act 1975 (Qld) and Building Regulation 2021 (Qld), changing the use of part of a building constitutes a change of classification.

This renovation would require:

• Building approval

• Assessment of construction type

• Verification of required FRLs

• Inspection and certification of passive fire systems

• Updated fire safety documentation

In many cases, fire engineering input is required where multiple classifications interact.

Key Risks in Mixed-Class Renovations

When Class 2, Class 6 and Class 9b uses combine, common risks include:

• Assuming existing construction is sufficient

• Failing to reassess construction type

• Overlooking service penetrations created during fitout

• Inadequate fire-stopping documentation

• Underestimating the impact of a Class 9b use

What appears to be a simple fitout can fundamentally alter the building’s fire compliance framework.

Conclusion

Building classification directly influences FRLs and passive fire requirements in Queensland. When multiple classifications — particularly Class 2, Class 6 and Class 9b — exist within one building, fire separation requirements become more stringent and complex.

Introducing retail and gym uses into a residential building is not merely a tenancy change — it reshapes the building’s risk profile under the NCC. Construction type, required FRLs, service penetrations and exit protection must all be reassessed.

For developers, body corporates and strata managers, understanding these interactions early can prevent costly rectification works and ensure compliance with Queensland’s building legislation — while maintaining occupant safety as the highest priority.

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References

Australian Building Codes Board. (2022). National Construction Code 2022, Volume One – Building Code of Australia (Class 2 to Class 9 buildings). Australian Government. https://ncc.abcb.gov.au

Australian Building Codes Board. (2022). National Construction Code 2022, Volume One – Specification C: Fire resistance and stability. Australian Government. https://ncc.abcb.gov.au

Australian Building Codes Board. (2022). National Construction Code 2022, Volume One – Section C: Fire resistance. Australian Government. https://ncc.abcb.gov.au

Queensland Government. (1975). Building Act 1975 (Qld). https://www.legislation.qld.gov.au

Queensland Government. (2021). Building Regulation 2021 (Qld). https://www.legislation.qld.gov.au

Queensland Fire and Emergency Services. (n.d.). Fire safety in buildings. Queensland Government. https://www.qfes.qld.gov.au

Standards Australia. (2018). AS 4072.1–2005 (R2016): Components for the protection of openings in fire-resistant separating elements—Part 1: Service penetrations and control joints. Standards Australia.

Standards Australia. (2014). AS 1530.4–2014: Methods for fire tests on building materials, components and structures—Part 4: Fire-resistance tests for elements of construction. Standards Australia.