NCC Building Classes Explained: Class 1 to 10, Every Sub-Class, Mixed Use and the 10% Rule (2025 Guide)

Every requirement in the National Construction Code (NCC) starts from one question: what class is the building? The class decides which volume of the Code applies, the Type of fire-resisting construction, the exits, the sprinklers, the toilets and the access. Get it wrong and every later answer is read from the wrong row.

This guide sets out the ten classes and their sub-classes as NCC 2025 Part A6 defines them, the tests that separate near neighbours, and how a building with several uses is classified. Every rule carries its clause. The finder in section 11 applies the definitions to your building.

In one minute

• Use decides the class. A building, or a part of one, is classified by the purpose it is designed, constructed or adapted for, and each part is classified on its own (A6G1(1), (2)).

• Nothing but a private garage may sit above or below a Class 1 house (Limitation to A6G2). Stack two dwellings, or put a shared carpark under a row of townhouses, and the dwellings are Class 2 (A6G3).

• The small-number tests are exact. A guest house is Class 1b up to 12 people and 300 m² of floor area (A6G2(2)(b)); past either limit it is Class 3. A building holds only one Class 4 dwelling (A6G5).

• A minor use of less than 10% of a storey may take the storey's class (A6G1, Exemption (1)), except a laboratory, an early childhood centre or a Class 2, 3 or 4 part (Limitation to A6G1).

• Volume One covers Classes 2 to 9; Volume Two covers Class 1, 10a, 10c and certain 10b structures (A1G1, A1G2). Part A6 is printed the same in both.

1. How a building is classified

A building or part of a building is classified by the purpose for which it is designed, constructed or adapted to be used (A6G1(1)). Each part is classified according to its purpose and must meet the requirements for that class (A6G1(2)). A part can carry more than one classification, and must then comply with the requirements of each (A6G12).

Two rules settle the spaces that serve the rest of the building:

• Plant rooms. A room containing a mechanical, thermal or electrical facility that serves the building takes the classification of the major part or principal use of the building or fire compartment it is in (A6G1(3)). An electricity network substation is excluded (A6G1, Exemption (2)).

• Rooftop terraces and the like. An occupiable outdoor area takes the classification of the part it is associated with, unless another is more suitable (A6G1(4)).

Where the classification is unclear, the appropriate authority decides, looking at what the building most closely resembles, its likely fire load and the risks to its users (A6G1 explanatory information).

2. The classes at a glance

Part A6 has ten classes, four of them divided into sub-classes. The groups below are a reading aid; the classes are the Code's.

Class	What it is	Clause
1a	A single dwelling: a detached house, or one of a group of two or more attached dwellings, each a building, separated by a fire-resisting wall (row house, terrace, town house, villa unit)	A6G2(2)(a)
1b	A boarding house, guest house, hostel or the like for not more than 12 people with not more than 300 m² of floor area; or four or more single dwellings on one allotment used for short-term holiday accommodation	A6G2(2)(b)
2	A building containing two or more sole-occupancy units, each a separate dwelling	A6G3
3	A residential building giving long-term or transient accommodation to a number of unrelated people: boarding houses, hostels and backpackers, the residential part of a hotel, motel, school or detention centre, staff quarters of a health-care building, accommodation for the aged, children or people with disability, and residential care buildings	A6G4
4	A dwelling in a Class 5, 6, 7, 8 or 9 building, if it is the only dwelling in the building	A6G5
5	An office building used for professional or commercial purposes	A6G6
6	A shop or other building for the sale of goods by retail or the supply of services direct to the public: cafes and restaurants, the dining room, shop or kiosk of a hotel or motel, hairdressers, public laundries, undertakers, supermarkets, showrooms, service stations	A6G7
7a	A carpark	A6G8(2)(a)
7b	A building used for storage, or for the display of goods or produce for sale by wholesale	A6G8(2)(b)
8	A laboratory, or a building where goods or produce for sale are produced, assembled, altered, repaired, packed, finished or cleaned	A6G9
9a	A health-care building, including its laboratories, and including a health-care building used as a residential care building	A6G10(2)(a)
9b	An assembly building, including a trade workshop or laboratory in a primary or secondary school	A6G10(2)(b)
9c	A residential care building	A6G10(2)(c)
10a	A non-habitable building: a private garage, carport, shed or the like	A6G11(2)(a)
10b	A non-habitable structure: a fence, mast, antenna, retaining or free-standing wall, swimming pool or the like	A6G11(2)(b)
10c	A private bushfire shelter	A6G11(2)(c)

Every class and sub-class of NCC 2025 Part A6, paraphrased from the clauses cited. Part A6 is printed the same in Volumes One and Two.

3. Class 1: houses, townhouses and small guest houses

A Class 1 building is a dwelling (A6G2(1)). Class 1a is one or more buildings which together form a single dwelling: a detached house, or one of a group of two or more attached dwellings, each being a building, separated by a fire-resisting wall, such as a row house, terrace house, town house or villa unit (A6G2(2)(a)). The explanatory information adds that a habitable outbuilding such as a sleepout is part of the dwelling, and that the number of storeys makes no difference.

The test that decides most borderline cases is the Limitation to A6G2: a Class 1 building cannot be located above or below another dwelling or another class of building, other than a private garage. A house may sit over its garage. It may not sit over a shop, a shared carpark or another dwelling.

Attached Class 1a dwellings are divided by a separating wall. It has an FRL of not less than 60/60/60, or is masonry at least 90 mm thick, and runs from the footings or slab to the underside of a non-combustible roof covering, or 450 mm above a combustible one (Housing Provisions 9.3.1).

Class 1b has two limbs (A6G2(2)(b)):

• A boarding house, guest house, hostel or the like that would ordinarily accommodate not more than 12 people and has a total area of all floors not more than 300 m², measured over the enclosing walls. Both limits must be met.

• Four or more single dwellings on one allotment used for short-term holiday accommodation, with no floor area limit (A6G2 explanatory information).

A Class 1b building is built under Volume Two like a house, with more smoke alarms: in every bedroom, every corridor or hallway serving a bedroom, and each other storey (Housing Provisions 9.5.3), plus lighting activated by the alarm to assist evacuation (9.5.5). Its access requirements are in Volume One D4D2(2): for holiday dwellings, 1 accessible in 4 to 10 and 2 in 11 to 40 (Table D4D2a).

4. Classes 2, 3 and 4: apartments, shared stays and the single dwelling

Class 2 is a building containing two or more sole-occupancy units, each a separate dwelling (A6G3). A sole-occupancy unit is a part of a building occupied by one owner, tenant or other occupier to the exclusion of any other (definition).

The line between Class 1a and Class 2 is drawn by what is above and below each dwelling, not by the number of storeys. The explanatory information to A6G2 and A6G3 makes it explicit:

• A residential sole-occupancy unit located over another is always Class 2 or Class 3, never Class 1.

• Single-storey attached dwellings with any common space below them are Class 2, whether or not that space is a storey.

• Class 2 dwellings can be attached to a building of another class.

Class 3 is a residential building providing long-term or transient accommodation for a number of unrelated persons (A6G4(1)): boarding houses and backpackers, the residential part of a hotel, school or detention centre, accommodation for the aged or people with disability, and the other uses listed in A6G4(2). The length of stay is unimportant (A6G4 explanatory information).

Class 4 is a dwelling in a Class 5, 6, 7, 8 or 9 building, if it is the only dwelling in the building (A6G5). A caretaker's flat and a flat over a shop are the common cases. The explanatory information spells out the consequences:

• A Class 4 part cannot be in a Class 1, 2 or 3 building, so a manager's flat in a motel is Class 1, 2 or 3 (A6G4 and A6G5 explanatory information).

• A building holds only one Class 4 dwelling. Two or more dwellings are Class 1, 2 or possibly 3.

• Renting the flat out does not change its class. Converting the shop below into a second flat makes both flats Class 2, or possibly Class 3.

5. Classes 5 to 8: offices, shops, carparks, warehouses and factories

Class 5 is an office building used for professional or commercial purposes (A6G6).

Class 6 is a shop or other building for the sale of goods by retail or the supply of services direct to the public (A6G7(1)). It includes cafes and restaurants; a hotel or motel's dining room, shop or kiosk, and any bar area that is not an assembly building; hairdressers, public laundries and undertakers; and supermarkets, showrooms and service stations (A6G7(2)). New South Wales adds a small live music or arts venue, and South Australia a small arts venue, in their own versions of A6G7.

Class 7a is a carpark: a building used for parking motor vehicles that is neither a private garage nor used for servicing vehicles other than washing, cleaning or polishing (A6G8(2)(a); definition). Class 7b is a building used for storage, or for the display of goods or produce for sale by wholesale (A6G8(2)(b)).

Some parking is not a carpark at all. In Volume One a private garage includes any single storey of a building of another class containing not more than 3 vehicle spaces, if there is only one such storey in the building (definition). That storey is Class 10a. A space holding only accommodation for not more than 3 vehicles is also not a storey (definition of storey).

Class 8 is a laboratory, or a building in which goods or produce for sale are produced, assembled, altered, repaired, packed, finished or cleaned (A6G9). A laboratory in a health-care building is part of the Class 9a, and a trade workshop or laboratory in a primary or secondary school is Class 9b (A6G10(2)).

6. Class 9: health care, assembly and residential care

Class 9a is a health-care building (A6G10(2)(a)), and the definition turns on evacuation: its occupants or patients undergoing medical treatment generally need physical assistance to evacuate. It includes a hospital; a nursing home or similar facility for sick or disabled persons needing full-time care; and a clinic, day surgery or procedure unit where the predominant treatment leaves patients non-ambulatory and needing supervised care for some time afterwards (definition).

Class 9b is an assembly building (A6G10(2)(b)). That is a building where people assemble for civic, theatrical, social, political or religious purposes; for education in a school, early childhood centre or preschool; for entertainment, recreation or sport, including a nightclub, a hotel or motel bar with live entertainment or a dance floor, a cinema or a stadium; or for transit, such as a station, airport or ferry terminal (definition). New South Wales and South Australia print their own versions of this definition.

Class 9c is a residential care building (A6G10(2)(c)): a place of residence where 10% or more of the residents need physical assistance with their daily activities and to evacuate, including an aged care building but not a hospital (definition). The same definition also reaches Class 3 and 9a buildings (A6G4(2)(g), A6G10(2)(a)). The explanatory information says Class 9c allows any mix of care needs, and lets the mix change without a new approval. Victoria prints its own definition of a residential care building.

7. Class 10: non-habitable buildings and structures

A Class 10 building or structure is non-habitable (A6G11(1)). Class 10a is a private garage, carport, shed or the like. Class 10b is a fence, mast, antenna, retaining or free-standing wall, swimming pool or the like. Class 10c is a private bushfire shelter (A6G11(2)).

The habitable line is firm. A sleepout, or a detached entertainment room on the same allotment as a house, is part of the Class 1 building and cannot be Class 10. A small toolshed used for hobbies or home repairs is Class 10a (A6G11 explanatory information).

Where a Class 10a building sits between or beside a house and a boundary that is not to a road or public space, or another building on the allotment, the house is protected by a method in Housing Provisions 9.2.5 to 9.2.7 (9.2.4). An open carport can be exempt under 9.2.8 if, among other conditions, two or more sides and at least a third of its perimeter are open and its roof covering is polycarbonate or non-combustible. A private garage above or below a house counts as part of the Class 1 building for its smoke alarms (Volume Two H3D6(2)). The Class 10a guide works through the methods, and the fire-rated walls guide covers house walls near a boundary.

A private bushfire shelter is associated with, but not attached to or part of, a Class 1a dwelling (definition). Volume Two covers it (A1G2). It must meet Performance Requirement H7P6, which has no Deemed-to-Satisfy Provisions (Volume Two H7D1(3)).

8. Mixed use, parts and the 10% rule

Each part of a mixed-use building is classified by its own purpose (A6G1(2)). The Code then deals with the parts in three ways.

Type of construction. A building of multiple classifications takes the most fire-resisting Type from Table C2D2, read as if the top storey's classification applied to every storey (Volume One C2D4(1)). A Class 4 part on the top storey is set aside, and the next storey down or the adjacent part is used instead (C2D4(2)). The Type A, B and C guide covers the rise in storeys that feeds the table.

Separation. Parts side by side in a storey take the higher FRL for each element or are separated by a fire wall (C3D9). Parts one above another are separated by the floor. In Type A it takes the FRL for the lower storey's class. In Type B or C, a floor under a Class 2, 3 or 4 part needs a ceiling with 60 minutes' resistance to the incipient spread of fire, an FRL of 30/30/30, or a fire-protective covering if it is combustible or metal (C3D10). The FRLs are explained in our FRL guide.

The 10% rule. Where a part of a storey is designed, constructed or adapted for a different purpose and is less than 10% of the floor area of that storey, the classification of the rest of the storey may apply to the whole storey (A6G1, Exemption (1)). The Limitation to A6G1 bars three minor uses from it: a laboratory, a Class 9b early childhood centre, and a Class 2, 3 or 4 part. The explanatory information cites a laboratory's fire hazard, the fire safety requirements of early childhood centres, and the fire and sound separation residents need.

It also gives the Code's own example. A single-storey factory with an office of 8% of its floor area may be Class 8 throughout; at 12% the office is Class 5. The rule changes the label, not the people: the occupant numbers in Table D2D18 and the Section J profiles are still read for the actual use of the minor area. The D2D18 guide explains the count.

9. What your class decides

These are the main places where the class changes the answer elsewhere in the Code.

What it decides	Where	How the class changes it
Which volume applies	A1G1, A1G2	Volume One: all Class 2 to 9 buildings, and access for Class 1b and 10a buildings and Class 10b pools. Volume Two: Class 1 and 10a buildings, Class 10c shelters and certain Class 10b structures
Type of construction	Volume One C2D2, C2D4	Two columns: Class 2, 3, 9 and Class 5, 6, 7, 8. At a rise of 3 storeys the first is Type A and the second Type B; at 2 storeys, Type B and Type C
Exits	D2D3	Class 2 to 8: 2 exits from each storey once the effective height is over 25 m, and from a Class 2 or 3 building built to C2D6. Class 9: also above a rise in storeys of 6, and from any storey with a patient care area, 9c sleeping areas or an early childhood centre, each storey of a school with a rise of 2 or more, and any storey for more than 50 persons
Sprinklers	E1D6 to E1D11	Class 2 and 3: throughout at a rise in storeys of 4 or more up to 25 m effective height. Class 9c, and a Class 3 or 9a residential care building: throughout. Class 6: compartments over 3 500 m² or 21 000 m³. Class 7a: over 40 vehicles. Early childhood centres: the whole building, with two exceptions
Access for people with a disability	D4D2	A rule per class: common areas for Class 2; a number of accessible units for Class 3 and 9c; all areas normally used for Class 5, 6, 7b, 8 and 9a; levels with accessible parking for Class 7a
Sanitary facilities	F4D2, F4D4	Class 2 and 4: within each unit. Class 3 and 9c residents: the ratios in F4D2. Otherwise Class 3 and 5 to 9: Tables F4D4a to F4D4l by use (see the sanitary facilities guide)
Sound insulation	F7D2; Volume Two H4D8	Part F7 applies to Class 2, 3 and 9c buildings. For Class 1, Volume Two H4D8 points to Housing Provisions Part 10.7
Energy efficiency	J2D2; Volume Two H6D2	Class 3 and 5 to 9: Parts J4 to J8 and parts of J9. A Class 4 part: Part J3. Class 1: Volume Two Part H6. Class 2 is dealt with by a note at the start of Part J1 (see the Section J guide)
Livable housing	G7D2; Volume Two H8D2	Each sole-occupancy unit of a Class 2 building, except Part 1 of the Standard, and every Class 1a dwelling (see the livable housing checklist)

Where NCC 2025 changes its requirements by class, summarised from the clauses cited. Each row has conditions and exceptions that the clause itself sets out.

10. Grey areas the Code settles

• Guest house or hotel. A guest house is Class 1b up to 12 people and 300 m², and Class 3 past either. The residential part of a hotel or motel is Class 3, and its dining room Class 6 (A6G2(2)(b), A6G4(2), A6G7(2)(b)).

• A shop with a flat above. One flat is a Class 4 part (A6G5). A second flat anywhere in the building makes both Class 2, or possibly Class 3 (A6G5 explanatory information).

• A home office. A study is a habitable room of the dwelling (definition of habitable room). Where part of a storey of a house is designed or adapted as an office for a business, the 10% exemption decides whether the whole storey stays Class 1 (A6G1, Exemption (1)). A larger office is its own class, so settle it with the building surveyor or certifier early.

• Carport or garage. Both are Class 10a (A6G11(2)(a)). The difference is in fire separation: an open carport can be exempt under Housing Provisions 9.2.8, and the note to that clause says a side closed by a vehicle access door is not an open side.

• A house over someone else's garage. A Class 1a dwelling may sit over a private garage (Limitation to A6G2). Where the garage serves another dwelling, the walls between need an FRL of 60/60/60 from the garage side, or 90 mm of masonry, up to a separating floor (Housing Provisions 9.4.1, 9.4.2).

11. Find the class of your building

Choose what the building is for, then answer the follow-up the definitions turn on: where the dwellings sit, how many people a guest house takes, how big the office in a factory is, or whether there is a flat in the building. The headline gives the class and the verdict the clause. The cards show the volume, the Table C2D2 pattern and the first things the class triggers.

12. Worked examples

Three townhouses over a shared basement carpark. The dwellings stand side by side with fire-resisting walls between them, over a basement all three share. With common space below, they are Class 2, not Class 1a (A6G3 explanatory information; Limitation to A6G2). Six car spaces is not a private garage, so the basement is a Class 7a carpark (definitions; A6G8(2)(a)), and the whole building is designed under Volume One.

A shop with one flat, then two. A two-storey shop with a flat above is Class 6 with a Class 4 part (A6G5). Table C2D2 is read as Class 6 (C2D4(2)): a rise of 2 gives Type C, and the floor under the flat follows C3D10. Convert the shop into a second flat and the building is Class 2: Type B, or Type C under C2D6 if each unit has access to at least two exits or its own direct access to a road or open space.

A guest house growing. Six bedrooms for 12 guests in 280 m² is Class 1b (A6G2(2)(b)(i)). Add a seventh room so it ordinarily takes 14, or extend it to 320 m², and it is Class 3 (A6G4(2)(a)). It moves to Volume One, with Part F7 sound insulation (F7D2) and one accessible room for up to 10 sole-occupancy units (Table D4D2b).

The office in a factory. In a single-storey factory of 2 000 m², a 160 m² office is 8% of the storey, and the whole storey may be Class 8 (A6G1, Exemption (1)). A 240 m² office, 12%, is a Class 5 part. A 200 m² office is exactly 10%: the clause says less than 10%, which it is not, but the explanatory information says 10% or less, so settle that case with the building surveyor or certifier. Either way the office occupants are counted at the office rate in Table D2D18.

Childcare in an office building. An early childhood centre taking 5% of a storey is still a Class 9b part, because the 10% rule never absorbs it (Limitation to A6G1). Its storey needs 2 exits (D2D3(4)), and sprinklers are required throughout the whole building, office floors included (E1D11(2)). The exception for a centre wholly within a storey with direct egress to a road or open space may apply on the ground floor; on level 3 it would not.

13. Common mistakes

• Townhouses over a shared space called Class 1a. A common carpark, store or lobby under the dwellings makes them Class 2, even when the space is not a storey (A6G3 explanatory information).

• A caretaker's flat called Class 4 in the wrong building. Class 4 exists only in a Class 5 to 9 building with no other dwelling (A6G5). In an apartment building or a motel the flat is Class 1, 2 or 3.

• The 10% rule used where it is barred. A laboratory, an early childhood centre and a Class 2, 3 or 4 part keep their own class however small they are (Limitation to A6G1). At exactly 10% the clause (less than 10%) and its explanatory information (10% or less) differ, so settle that case with the building surveyor or certifier.

• A sleepout called a shed. A habitable outbuilding is part of the Class 1 building (A6G11 explanatory information).

• A hotel bar with a dance floor called Class 6. A hotel or motel bar with live entertainment or a dance floor is an assembly building, Class 9b. Only a bar area that is not an assembly building is Class 6 (definition; A6G7(2)(b)).

14. Where to read the source

Part A6 (A6G1 to A6G12) is printed the same in NCC 2025 Volumes One and Two. Each volume's scope is in A1G1 and A1G2, and the definitions Part A6 relies on are in each volume's definitions schedule. The clauses the class feeds are named against each row of the table in section 9. All are free to read on the NCC website, with the explanatory information quoted here.

Inside AEC Assistant the Code text is searchable by clause. Ask whether a shop with two flats above it has a Class 4 part and the answer comes back with the clause it was read from. This article is general guidance. The building surveyor or certifier for your project determines compliance.