Fire Safety Requirements for Class 2 Buildings: BCA Section C Compliance in NSW

By Franz Phan, Registered Design Practitioner (giantA Pty Ltd) — 15+ years specialising in Class 2 multi-unit residential design and Building Code compliance across NSW.

Class 2 buildings — apartments, units and residential flat buildings — represent the most tightly regulated residential construction type under the National Construction Code (NCC). Because occupants sleep above and below unrelated neighbours, the Building Code of Australia (BCA) Section C imposes stringent fire-resistance, compartmentation and egress requirements that far exceed those for single detached dwellings.

For developers and builders in NSW, failure to meet these requirements at design stage is the single most expensive correction you can make. A mid-rise apartment project in Parramatta we reviewed in early 2025 required $340,000 in retrospective fire-separation upgrades because the initial designer had treated it as a Class 1a attached dwelling. That experience is why I am writing this guide.

What Is a Class 2 Building Under the BCA?

A Class 2 building is defined in Section A of the BCA as a building containing two or more sole-occupancy units where people reside above and below each other. This includes apartment blocks, residential flat buildings, and attached dwellings over a common basement or car park. A single-storey attached dwelling on slab is Class 1a; the moment it stacks over a shared carpark, it becomes Class 2 — and the fire-safety rules change entirely.

From 1 July 2024, all Class 2 buildings in NSW fall under the Design and Building Practitioners Act 2021 (DBP Act). This means every fire-resistance design, every fire-separation detail and every structural fire-protection calculation must be prepared or reviewed by a registered design practitioner or registered architect, then lodged as a Design Compliance Declaration (DCD) before construction can commence.

Source: BCA Section A6; NSW Government — Building classes and roles of professionals under the DBP scheme.

Type of Construction: Why Class 2 Buildings Must Be Type A, B or C

BCA Section C2D2 sets the minimum type of construction required based on the building's class and rise in storeys. For Class 2 buildings, the thresholds are:

Source: BCA Section C2D2 (NCC 2022).

Type A construction is the most fire-resistant. It requires that all loadbearing elements achieve a specific Fire Resistance Level (FRL), expressed as three numbers: structural adequacy / integrity / insulation. For example, an FRL of 90/90/90 means the element must maintain structural loadbearing capacity for 90 minutes, resist flame passage for 90 minutes, and limit temperature rise for 90 minutes.

In practice, a four-storey apartment building in Sydney's inner west must be Type A. That means the concrete slab between floors must achieve at least FRL 120/120/120 if it is loadbearing and separating sole-occupancy units. The walls between units must achieve FRL 90/90/90. The stairwell enclosure must achieve FRL 120/120/120. These are not optional upgrades — they are mandatory Deemed-to-Satisfy provisions under Specification 5 of the BCA.

Fire Resistance Levels (FRL): The Numbers That Matter

Specification 5 of the BCA provides the exact FRL tables for Type A, B and C construction. For Class 2 buildings, the most commonly referenced FRLs are:

Source: BCA Specification 5 (NCC 2022), Tables S5C11a–S5C11g.

The distance to a fire-source feature — typically the nearest boundary or another building on the same site — is critical. A loadbearing external wall less than 1.5 metres from a boundary must achieve FRL 180/180/180 in Type A construction. At 3 metres, the same wall may achieve FRL 120/120/120. At 6 metres or more, it may drop to FRL 90/90/90. These distances are measured from the external face of the wall to the boundary, not from column centres. Getting this wrong at DA stage forces a redesign of the floor plate or a costly upgrade to the wall system.

Sprinklers, Detection and Egress: The Active Fire Systems

Beyond passive fire resistance, Class 2 buildings require active fire protection systems under BCA Section E. The critical triggers are:

Sprinkler systems (E1D4): Class 2 buildings of four or more storeys must have a sprinkler system complying with Specification 17 installed throughout. There is no exemption for small floor plates or boutique developments. A three-storey building may avoid sprinklers if it meets Type B construction, but the moment you add a fourth level, the sprinkler requirement triggers automatically.

Smoke detection: Smoke alarms must be installed in every sole-occupancy unit and in common corridors, in accordance with AS 3786. For new Class 2 buildings, interconnected photoelectric smoke alarms are mandatory under NSW legislation.

Egress paths (Section D): Every sole-occupancy unit must have access to at least two exits if the building exceeds a rise in storeys threshold, or if the travel distance to a single exit exceeds 20 metres. Stairways must be fire-isolated — meaning they are enclosed in construction with the FRL prescribed for the building type — and must discharge directly to open air or a fire-isolated passageway.

In a 2024 project we designed in Ashfield — a 12-unit, four-storey apartment building over a single basement carpark — the egress analysis took three weeks. The stairwell location dictated by BCA Section D influenced the entire floor-plate geometry. Moving the stairwell two metres east would have reduced the corner apartment's bedroom width below the minimum BCA requirement. These are the real-world trade-offs that developers need to understand before they commit to a site layout.

Compartmentation: Keeping Fire Inside the Unit

BCA Section C3 requires that Class 2 buildings be divided into fire compartments to limit the spread of fire. A fire compartment is defined as the part of a building bounded by fire-resisting walls and floors that will prevent fire spread for a specified time.

For Class 2 buildings, the primary compartmentation is the sole-occupancy unit itself. The walls and floors between units must achieve the FRL prescribed in Specification 5, effectively making each apartment its own fire compartment. Common areas — corridors, foyers, stairwells — form separate compartments and must be separated from the units by fire-resisting construction.

One of the most common compliance failures we see in DCD reviews is the penetration of services through fire-rated walls and floors without appropriate fire stopping. A plumbing pipe passing from one unit to another through an FRL 90/90/90 wall must be fire-stopped with a system tested to AS 4072.1 and AS 1530.4. The same applies to electrical conduits, HVAC ductwork and data cabling. At giantA, we require a fire-stopping schedule on every Class 2 project before we will sign the DCD.

Acoustic and Separation Overlap: When Fire and Sound Meet

There is a practical overlap between fire-resistance and acoustic separation in Class 2 buildings. BCA Section F7 requires that walls between sole-occupancy units achieve an airborne sound insulation rating of Rw + Ctr ≥ 50, and that separating floors achieve both airborne (Rw + Ctr ≥ 50) and impact (LnT,w ≤ 55) ratings.

Many wall systems that satisfy the FRL 90/90/90 requirement — such as double-stud plasterboard walls with insulation — also satisfy the acoustic requirement. However, lightweight systems that rely on fire-rated plasterboard alone may not achieve the mass needed for Rw 50. We encountered this exact issue on a 2023 project in Bankstown where the specified lightweight steel-stud wall achieved FRL 90/90/90 but only reached Rw 42 in laboratory testing. The solution was to upgrade to a heavier stud section and add acoustic batts — a $12 per square metre increase that, across 24 units, added $8,600 to the build cost but avoided a Design Compliance Declaration rejection.

Source: BCA Section F7 (NCC 2022); AS/NZS ISO 717.1; AS/NZS ISO 717.2.

Real-World Project Examples

Example 1: 8-unit apartment, Merrylands (2024)

A developer approached us after receiving a DA condition requiring confirmation of Type B construction compliance for a three-storey walk-up. The original designer had assumed Type C construction applied because the building was only three storeys. BCA C2D2 makes clear that three storeys for Class 2 triggers Type A, not Type B or C. We revised the structural fire-protection schedule, upgraded the floor system to achieve FRL 120/120/120, and resubmitted the DCD. The DA was approved six weeks later. Total additional cost: $45,000. Cost if discovered during construction: an estimated $180,000 in demolition and rework.

Example 2: 20-unit mixed-use, Parramatta (2025)

This four-storey building combined ground-floor retail (Class 6) with residential apartments (Class 2) above. The BCA treats mixed-use buildings as multi-classified, meaning each class must meet its own Section C requirements, and the separation between classes must achieve the higher FRL. The floor between retail and residential required FRL 120/120/120 with no penetrations except fire-stopped services. We designed a 200 mm post-tensioned concrete slab with intumescent coating to the steel edge beams. The DCD was accepted on first review by the certifier. Project timeline: 14 weeks from DA lodgement to construction certificate.

Example 3: Boutique 6-unit conversion, Newtown (2023)

A heritage warehouse conversion into six strata apartments. The existing timber structure could not achieve the required FRL for Type A construction. We pursued a Performance Solution under BCA Section A5, using fire engineering modelling to demonstrate that the building's limited rise (two storeys), enhanced sprinkler coverage and early-warning smoke detection provided an equivalent level of safety to the Deemed-to-Satisfy provisions. The Performance Solution added $22,000 in consultant fees but preserved the original timber character that made the project marketable. All six units sold off-the-plan within four weeks.

FAQ: Fire Safety for Class 2 Buildings

Does every Class 2 building need sprinklers?

No. Sprinklers are only mandatory for Class 2 buildings of four or more storeys under BCA E1D4. A two-storey Class 2 building of Type B construction does not require sprinklers under the Deemed-to-Satisfy provisions, though many developers install them voluntarily for insurance and marketability benefits.

What is the difference between Type A and Type B construction for apartments?

Type A construction requires higher FRL ratings for all structural and separating elements — typically FRL 90/90/90 or 120/120/120. Type B construction allows lower ratings, such as FRL 60/60/60 for internal walls, and is only permitted for Class 2 buildings up to two storeys. A three-storey Class 2 building must be Type A.

Who can sign the Design Compliance Declaration for fire-resistance design?

Under the DBP Act 2021, fire-resistance design for Class 2 buildings must be prepared or reviewed by a Registered Design Practitioner (RDP) or Registered Architect. The RDP must hold the appropriate category of registration — for fire engineering, this is typically "Fire Safety" or "Structural" depending on the element. The DCD is lodged through the NSW Planning Portal before construction begins.

Can I use a Performance Solution instead of Deemed-to-Satisfy for fire safety?

Yes, under BCA Section A5. A Performance Solution uses fire engineering analysis to demonstrate that the proposed design achieves an equivalent or greater level of safety than the Deemed-to-Satisfy provisions. This requires a qualified fire engineer and typically adds $15,000–$40,000 in consultant fees. It is commonly used for heritage conversions, atypical geometries or cost-driven value engineering.

What fire-stopping standards apply to service penetrations?

All service penetrations through fire-rated walls and floors must be fire-stopped in accordance with AS 4072.1 (Components for the protection of openings in fire-resistant separating elements) and tested to AS 1530.4 (Methods for fire tests on building materials, components and structures). The fire-stopping system must achieve the same FRL as the element it penetrates.

How does the DBP Act affect fire-resistance documentation?

From 1 July 2024, every Class 2 building in NSW requires a Design Compliance Declaration (DCD) lodged on the NSW Planning Portal before a Construction Certificate can be issued. The DCD must include fire-resistance schedules, construction details and evidence that registered practitioners have reviewed the design. Incomplete or incorrect fire-resistance documentation is the most common reason for DCD rejection.

Do fire doors need to be self-closing?

Yes. Under BCA Section C, fire doors in Class 2 buildings must be self-closing and achieve the FRL required for the wall in which they are installed. In Type A construction, this is typically a self-closing door with an FRL of at least –/60/30. Fire doors must not be propped open and must be inspected annually under AS 1851.

What is the most common fire-safety compliance failure in Class 2 DA submissions?

Misclassification of the building type — treating a Class 2 building as Class 1a to avoid Type A construction requirements. The second most common failure is inadequate fire-stopping schedules for service penetrations. The third is insufficient egress analysis, particularly in buildings with non-rectangular floor plates where travel distances are difficult to measure.

Conclusion

Fire safety compliance for Class 2 buildings is not a post-design checklist. It is a fundamental constraint on the building's geometry, structure, services and cost. Getting it right at the concept stage — with a Registered Design Practitioner who understands BCA Section C in detail — saves developers months of delays and hundreds of thousands of dollars in retrospective upgrades.

At giantA, we prepare fire-resistance schedules, compartmentation plans and DCD documentation as standard deliverables for every Class 2 project. If you are planning an apartment development in NSW and need certainty on your fire-safety compliance pathway, contact us for a Design Compliance readiness review.

Contact: Franz Phan, Registered Design Practitioner
Email: he@gianta.com.au
Phone: 0451 681 088
Website: gianta.com.au