BCA Section C Fire Resistance Notes (NCC 2022)

1. Introduction

• 1.1 General Principles
  • The fire resistance of Class 2 to 9 buildings is regulated through Section C of the Building Code of Australia Volume 1 (BCA).
  • Section C covers fire resisting construction (fire rating requirements for building elements), fire separation/compartmentation of buildings into ‘fire resisting cells’, and the ‘protection of openings’ in elements required to be fire resisting.
  • Section C contains Performance Requirements and prescriptive Deemed-to-Satisfy (DTS) provisions. When a design proposes an alternative to the DTS provisions, a Performance Solution may be developed under Part A2 of the BCA.
  • These notes provide an overview of the main concepts in Section C; they are educational and not a substitute for the BCA or the International Fire Engineering Guidelines.
• 1.2 Topic Objectives
  • On successful completion, you will be able to:
  • a) Understand the concept of fire resistance as related to Section C.
  • b) Apply knowledge of the practical design process used by the industry.
• 1.3 Overview
  • Section C of the BCA contains four parts:
  • a) Part C1 – Fire resistance
  • b) Part C2 – Fire resistance and stability
  • c) Part C3 – Compartmentation and separation
  • d) Part C4 – Protection of openings
  • Part C1 contains objectives, functional statements, Performance Requirements (relevant for Performance Solutions), and Verification Methods.
  • Part C2 primarily deals with fire resisting construction requirements (fire ratings), fire hazard properties, and design requirements for Fire Brigade intervention.
  • Part C3 deals with compartmentation and separation to limit fire size/spread and facilitate Fire Brigade intervention.
  • Part C4 regulates protection of openings (doors, windows, penetrations) in fire resisting construction.
• 1.4 Performance requirements
  • Compliance can be achieved via:
  • a) A Performance Solution addressing the relevant Performance Requirements, or
  • b) A Deemed-to-Satisfy Solution (DTS), or
  • c) A combination of both approaches (Part A).
  • The Performance Requirements (C1P1–C1P9) include:
  • a) C1P1 – Structural stability during fire.
  • b) C1P2 – Avoid spread of fire to exits, sole-occupancy units, public corridors, and between buildings.
  • c) C1P3 – Protect from spread of fire and smoke to allow evacuation (Class 9a health-care and Class 9c care buildings only).
  • d) C1P4 – Maintain tenable conditions during evacuation; resist spread of fire, smoke, heat, and toxic gases.
  • e) C1P5 – External concrete walls unlikely to collapse as a complete panel outward (in event of fire).
  • f) C1P6 – Avoid spread of fire from high-fire-h hazard or explosive service equipment.
  • g) C1P7 – Ensure emergency equipment can operate for the required time during a fire.
  • h) C1P8 – Fire resistance elements provided to resist spread around/openings/constructions joints and penetrations.
  • i) C1P9 – Provide access for fire brigade vehicles and personnel to the building.
• 1.5 DTS provisions
  • The DTS provisions in Section C comprise four parts: Part C1 (Fire resistance), Part C2 (Fire resistance and stability), Part C3 (Compartmentation and separation), Part C4 (Protection of openings).
  • Part C1 contains objectives, functional statements, Performance Requirements, and Verification Methods, generally used when a Performance Solution is proposed.
  • Part C2 contains the DTS provisions for fire resisting construction, non-combustibility for external walls/attachments, fire hazard properties, and fire brigade intervention requirements, depending on building characteristics (height, size, use).
  • Part C3 contains the DTS provisions for compartmentation and separation (size of compartments, separation between compartments, and additional requirements for Fire Brigade intervention).
  • Part C4 contains the DTS provisions for protection of openings (doors/windows) to reduce fire spread and facilitate Fire Brigade access/intervention.
  • DTS documents address specific scenarios (e.g., protection of openings near boundaries, penetrations) and provide acceptable methods for compliance.

2. Types of Fire Resisting Construction

• 2.1 Overview
  • Determining fire resistance requirements (fire rating) requires first selecting the Type of Fire Resisting Construction.
  • There are three Types of Construction: Type A (most fire resistant), Type B, and Type C (least fire resistant).
  • The required Type is determined from Table C2D2 and Specification 5, subject to exemptions in C2D6, C2D4(2), and C2D8 for special cases.
  • Characteristics by Type:
  • Type A: Higher FRLs; commonly required for higher-rise or larger floor area/volume; loadbearing walls typically concrete or masonry; external walls often non-combustible; protective measures to prevent vertical spread.
  • Type B: Generally lower FRLs than Type A; external walls typically non-combustible; some elements may require FRLs depending on class and location.
  • Type C: Low-rise with little or no FRLs; external walls can have FRLs limited by distance from a fire source feature (often none beyond 3 m).
• 2.2 Determining the classification and Rise in Storeys
  • The Type of Fire Resisting Construction is based on:
  • Building classification (A6), Rise in Storeys (C2D3), and floor area/volume (C3D3).
  • Step 1: Determine the classification from Part A6 (A6G1–A6G11), e.g., Class 1–10a/b etc.
  • Step 2: Determine the Rise in Storeys from C2D3 (and refer to Schedule 1 for storey definitions).
  • Building classifications include: Class 1 (1a dwelling, 1b boarding house), Class 2 (two or more sole occupancy units), Class 3 (residential buildings other than Class 1 or 2), Class 4 (the only dwelling in a building that is Class 5–9), Class 5 (offices), Class 6 (shops), Class 7a (carparks), Class 7b (storage/display), Class 8 (process or factory), Class 9a (health-care), Class 9b (assembly), Class 9c (residential care), Class 10a (non-habitable), Class 10b (carport/awnings).
  • Rise in Storeys (C2D3) – there are concessions where a storey does not count if it is on top of a building and contains only ventilating equipment or is partly below finished ground; alternatively, a single storey may count as two storeys in certain Class 7/8 situations with average internal height > 6 m.
  • A storey definition for Rise in Storeys uses Schedule 1 of the BCA; the Rise in Storeys is not the same as the number of storeys in a building – a building may have 4 storeys but a Rise in Storeys of 3, for example.
  • Rise in Storeys considerations include: collapse onto adjoining buildings, exposure to fire in other buildings, burnout of contents to allow safe evacuation, how occupants evacuate, firefighting/intervention requirements.
• 2.2.9 Determining preliminary Type of Construction
  • After classification and Rise in Storeys are determined, apply C2D2 and Table C2D2 to determine the preliminary Type of Construction.
  • The concept of “Minimum Type of fire resisting construction” may be increased to address floor area/volume. If the floor area/volume exceeds Type C limits, escalate to Type B (and so on) with all corresponding Type B requirements.
  • The preliminary Type may be adjusted by floor area and volume limits described in Table C3D3; if exceeded, consider moving to a higher Type or splitting into fire compartments.
• 2.2 Worked examples
  • Worked Example 1 – Rise in Storeys
  • Information: two buildings; Building 1 – 3 storeys above ground; Building 2 – 2 storeys above ground and 1 below ground; both buildings have three and two storeys above ground respectively.
  • Task: determine Rise in Storeys and number of storeys in each building.
  • Answer: Building 1 has Rise in Storeys = 3; Building 2 has Rise in Storeys = 2 (the storey below ground is not counted in Rise in Storeys).
  • Worked Example 2 – Preliminary Type of Construction
  • Information: Building 1 (3-storey Class 5 office) Rise in Storeys = 3; Building 2 (3-storey Class 5 office) Rise in Storeys = 2.
  • Result: Building 1 requires Type B construction; Building 2 requires Type C construction (based on Table C2D2).
  • Worked Example 3–5 discuss large isolated buildings and related open space/sprinkler requirements; see section 2.3 for full narrative and worked-illustration references.
• 2.3 Floor area and volume limitations
  • C2D2 requires the minimum Type of fire resisting construction per Table C2D2 and Specification 5, subject to exemptions in C2D2(1).
  • Type A construction provides highest fire resistance; Type C provides the least.
  • C2D4 deals with multi-classification buildings: the required Type of construction for the entire building is the most fire-resisting Type resulting from applying Table C2D2 to the top-storey classification.
  • C3D3 prescribes maximum floor area and volume limits within a fire compartment for each Type of construction.
  • C3D3 limitations can be exempted or relaxed for certain cases:
  • Carparks with sprinkler systems (Specification 17) and open deck carparks/open spectator stands.
  • Large Isolated Buildings (C3D4/C3D5) exemptions to C3D3 where the building is large but protected (e.g., sprinklers and 6 m wide open space around the building).
  • Parts of a building that only include HVAC, lifts, water tanks, or similar top-of-building services may not count toward the floor area/volume calculations for a fire compartment.
  • Atriums: portions counted/not counted in volume depending on bounding floors and openings.
  • If a building exceeds C3D3 limits, multiple compartments can be created to maintain preliminary Type; the DTS provisions for fire separation (C3D8, C3D2) may apply to treat parts as separate compartments.
  • Large Isolated Buildings (C3D4/C3D5) - criteria include open space and sprinklers; examples include shopping centres and warehouses. See Worked Example 4 and Worked Example 5.
  • Worked Example 3–5 illustrate how to determine whether a building can be treated as a Large Isolated Building and the implications for sprinkler coverage and vehicular access around the perimeter.

3. Part C2 Fire Resistance and Stability

• 3.1 Fire resistance levels and fire source features
  • FRLs rely on fire resisting construction (fire rating) and fire source exposure concepts, including fire hazard properties of materials (internal linings, non-combustibility requirements).
  • FRLs are expressed as a sequence of three numbers: structural adequacy / integrity / insulation.
• 3.2 Defining Fire resistance levels and a fire source feature
  • FRL format: The FRL is expressed as a triple in the order: structural adequacy / integrity / insulation: e.g., $FRL = 90/60/30$; a dash (–) means no requirement for that criterion. Example: $90/–/–$ means FRL only required for structural adequacy.
  • Structural adequacy relates to maintaining stability and loadbearing capacity (AS 1530.4).
  • Integrity relates to resisting passage of flames/hot gases (AS 1530.4).
  • Insulation relates to keeping the external surface temperature under specified limits (AS 1530.4).
  • FRL examples and interpretation:
  • A doorway to a residential sole-occupancy unit (Class 2) of Type C construction must be self-closing, tight-fitting, solid-core not less than 35 mm; whereas Type A requires self-closing –/60/30 door.
  • A floor on the 2nd floor in a Class 5 building of Type A construction must achieve $FRL = 120/120/120$; a Type C floor on the 2nd floor does not require an FRL.
  • External walls: FRL for external walls depends on building classification, Type of Construction, and exposure to a fire source feature.
  • Fire source feature: defined as the far boundary of road/river/lake, or a side/rear boundary of the allotment, or an external wall of another building on the same allotment not Class 10. Exposure is measured by horizontal distance to the feature.
  • Measurement of exposure: exposure is calculated along any horizontal straight line between the external wall and the fire source feature (or its vertical projection), with some exceptions if intervening walls have FRL not less than 30/–/– or are non-transparent.
  • Differences between Volume 1 and Volume 2: exposure measurement methods differ; general concept is the same but measurement standards vary.
  • Additional notes on exposure: if distances apply differently for separate parts of an element, the part with the least distance governs the FRL for that element; or apply part-by-part FRLs where appropriate.
• 3.2.6 FRLs – practical notes
  • FRLs can be derived via exact calculations in Specification 1 or via tested reports (e.g., AS 1530.4) that demonstrate a particular FRL.
  • External wall FRLs are determined by classification, Type of Construction, and exposure to fire source features.
• 3.3 Type A, B and C Construction
  • Specification 5 structure:
  • S5C2–S5C10: General requirements for all Types.
  • S5C11: Type A fire resisting construction (FRLs for building elements).
  • S5C21: Type B fire resisting construction (FRLs for building elements).
  • S5C24: Type C fire resisting construction (FRLs for building elements).
  • Worked Examples (from Specification 5):
  • Worked Example 6 – FRL for floor (Type A): ground floor FRL = $90/90/90$; floor laid directly on the ground may not need FRL per S5C12.
  • Worked Example 7 – FRL for floor between Class 2 and Class 6 (Type A): floor for Class 2 = $90/90/90$; separating floor FRL = $180/180/180$ (C3D10).
  • Worked Example 8 – FRL for floor (Type B): two-storey Class 9b assembly building; no FRL required for the first-floor (per S5C21a–g), separating construction must be fire resisting per S5C21(1, f).
  • Worked Example 9 – FRL for external wall (Type B): loadbearing external wall FRL = $120/30/30$; non-loadbearing portion has no FRL.
  • Worked Example 10 – FRL for external wall (Type C): with external walls near boundaries; refer to S5C24 for FRLs.
  • 3.3.4–3.3.5 worked examples illustrate how FRLs are allocated to floors and walls based on Type and separation requirements.
• 3.4 Fire Hazard Properties and Non-combustibility requirements
  • In addition to FRLs, Section C2 includes fire hazard properties and non-combustibility requirements for linings and external wall components (internal linings, fire hazard limits).
  • C2D11 and Specification 7 specify DTS for linings and materials and their limitations to limit fire growth and smoke.
  • C2D10 and C2D14 cover non-combustibility requirements for external walls and attachments; generally, all elements in external walls must be non-combustible, with exceptions for minor components (caulking, sealants, termite management, etc.).
• 3.5 Other considerations
  • Practical and overarching considerations:
  • Parts providing necessary support to achieve an FRL for structural adequacy must have FRLs not less than the supported part; where there is support, the supporting part must have an FRL not less than the supported part or greater in respect to structural adequacy (S5C3).
  • Some concessions exist (e.g., roofing providing lateral support under certain conditions).
• 3.5 Worked examples
  • Worked Example 11 – Lateral support to a fire resisting wall (Type C construction): roof frame provides lateral support; S5C3 concession allows roof to not achieve FRL for structural adequacy if providing lateral support.
  • Worked Example 12 – Lateral support to a fire resisting wall: steel columns/frames provide lateral support; concessions apply to external walls for structural adequacy but not to overall FRL for the wall.

4. Part C3 (Compartmentation and separation)

• 4.1 Compartmentation and separation
  • The aim is to limit fire size and spread and facilitate Fire Brigade intervention.
  • C3D3 regulates the size of fire compartments; C3D4/C3D5 provide concessions from large isolated building requirements.
  • Some buildings (e.g., sprinkler-protected carparks, open deck carparks, open spectator stands) may be exempt from certain DTS provisions in Table C3D3.
  • Class 2, 3, or 4 buildings are typically not referenced in Table C3D3 due to the extent of required fire separation; they are treated as multiple compartments within a single building with internal separations (C4D12).
• 4.2 Vertical separation of openings in external walls (C3D7)
  • Applies to Type A construction (except open deck carparks, open spectator stands, or sprinkler-protected buildings).
  • Aims to prevent fire spread between storeys via external wall openings.
  • C3D6 contains special requirements for early childhood centres (ECC) within mixed-use or multi-storey buildings, including requiring multiple compartments per storey and FRL requirements for ECC-related separations.
  • C3D7 specifics:
  • If any part of a window/opening in an external wall is above another opening in the storey below with a vertical projection close to the lower opening (e.g., within 450 mm horizontally), then separation is required by spandrel provisions or curtain wall/panel walls with FRLs and non-combustible materials, including specific dimensions (e.g., spandrel height at least 900 mm, extends 600 mm above upper surface, FRL at least 60/60/60, non-combustible).
  • C3D7 exclusions: open-deck carparks, open spectator stands, sprinkler systems throughout, openings within the same stairway, or openings where the floor between storeys does not require an FRL for integrity/insulation.
  • Figure references illustrate spandrel separation concepts (Figure 4 in guide).
• 4.3 Separation by fire walls (C3D8–C3D10)
  • C3D8 provides separation of fire compartments and a mechanism to treat a fire-walled portion of a building as a separate building for the purposes of DTS under Sections C, D and E if conditions are met (wall extends through all storeys, to underside of roof, and certain roof conditions).
  • C3D9 requires higher FRLs in the same storey when combining different classifications; separation by a fire wall with the higher FRL can be used.
  • C3D10 requires separation of classifications across different storeys, with FRLs or protective floor/ceiling systems to ensure proper separation when different classifications exist above/below.
  • Fire walls and separation around services (C3D13 & C3D14) specify separation for emergency equipment and other critical services.
  • Practical examples illustrate how to achieve separation across storeys and classifications using fire walls and associated FRLs.
  • A typical example (Figure 6) demonstrates compliance with C3D10 for separating different classes across storeys.

5. Part C4 (Protection of openings)

• 5.1 Protection of openings
  • Part C4 deals with protection of openings in fire resisting elements and is read in conjunction with C3 to maintain compartmentation.
  • C4D2 defines openings that count as openings in building elements required to have an FRL (doorways, windows/infill panels, fixed or openable glazed areas not having the FRL).
  • Openings between columns/beams at external edges or perimeters may be treated as external wall openings.
• 5.2 Protection of external wall openings
  • C4D3 requires protection for external-wall openings that must have an FRL and are within specified distances to fire source features:
  • i) within 3 m of a side or rear boundary; or
  • ii) within 6 m of the far boundary of a road/river/lake, if not at ground level; or
  • iii) within 6 m of another building on the allotment not Class 10.
  • C4D3 also requires that an opening required to be protected must not occupy more than 1/3 of the area of the external wall in the storey unless it is in a Class 9b building used as an open spectator stand.
  • Exemptions exist for certain circumstances (e.g., some openings in masonry walls, vehicle ramps in car parks).
• 5.2.4 Acceptable methods of protection (C4D5)
  • Doorways: self-closing or automatic closing doors, with wall-wetting sprinklers as appropriate; or fire doors with FRL not less than –/60/30 (self-closing or automatic closing).
  • Windows: wall-wetting sprinklers, or fire windows with FRL –/60/– or automatic fire shutters.
  • Other openings: wall-wetting sprinklers, or construction with FRL not less than –/60/–.
  • Figure: typical example of wall-wetting sprinkler protection for window openings.
• 5.3 Protection of internal openings
  • Protection of openings in floors and walls that must achieve an FRL is addressed by C4D12–C4D14 and Spec 13.
  • Common examples include:
  • Doorways in fire isolated exits, fire walls, and bounding construction in Class 2/3/4 parts.
  • Openings in floors for services (e.g., service risers, pipes, wiring).
  • Openings in walls for services (e.g., ducts, pipes, mechanical ductwork).
  • Typical protections include:
  • Fire doors in certain configurations (e.g., doors in fire isolated stairs) – self-closing doors with appropriate FRLs.
  • Provisions for doors open to corridors depending on construction type (Type A vs. Type B/C).
  • Fire collars around PVC pipes penetrating fire resisting walls/floors; intumescent material to seal around penetrations.
  • Fire dampers for duct penetrations and proper joint sealing with fire stopping materials.
  • Common problems include gaps around doors, non-tested door hardware, missing seals or improper tagging (tagging indicates FRL on the door/frame).
  • Installation notes reference AS1905.2015 for fire doors.
• 6 Conclusion
  • The fire resistance of Class 2–9 buildings is regulated through Section C (Parts C1–C4):
  • C1 – Fire resistance (FRLs and Performance Requirements)
  • C2 – Fire resistance and stability
  • C3 – Compartmentation and separation
  • C4 – Protection of openings
  • The DTS provisions (Parts C1–C4) provide the prescriptive pathways to compliance, while Performance Solutions provide an alternate pathway when appropriate.
  • The nine Performance Requirements (C1P1–C1P9) guide the required outcomes for fire safety and the design process.
  • Key components to consider in practice include FRLs, exposure to fire source features, compartment sizes, location of openings, protection of openings, and ensuring Fire Brigade access/intervention capabilities.

6. References

• Australian Building Codes Board (ABCB). (2022). The National Construction Code: Building Code of Australia 2022, Volume One. Canberra, Australia.
• Australian Building Codes Board (ABCB). (2019). The National Construction Code: Guide to Volume One. Canberra, Australia.
• Notes reference multiple sections and figures from the BCA Guide and NCC (as cited in the transcript).