Type A, B and C Construction in the NCC: How Rise in Storeys and Class Set the Type, Effective Height, and What Each Type Changes (2025 Guide)
Table C2D2 of NCC Volume One sets a building's Type of construction from two facts: its class and its rise in storeys. This guide explains how C2D3 counts storeys on a sloping site, with basements, rooftop plant, mezzanines and tall industrial storeys, how effective height differs, the two-storey concession, and what Type A, B or C changes beyond FRLs. A section builder counts the storeys and gives the Type.
Every Class 2 to 9 building is built to one of three Types of fire-resisting construction: A, B or C. The Type sets the fire-resistance level (FRL) of almost every wall, floor and column, and decides which parts must be non-combustible. It comes from two facts: the building's class and its rise in storeys. The class is usually clear. The rise in storeys is where projects go wrong, because it is not the number of floors on the drawings.
This guide follows the National Construction Code (NCC) 2025, Volume One Part C2. It sets out Table C2D2, then how C2D3 counts storeys on a sloping site, with basements, rooftop plant, mezzanines and tall industrial storeys. It covers effective height, the concessions that change the Type and what each Type changes beyond FRLs. The section builder in section 8 does the count for your building.
In one minute
Two inputs set the Type: rise in storeys and class. Four or more storeys is Type A for every class, and one storey is Type C for every class. In between, Class 2, 3 and 9 buildings take a more fire-resisting Type than Class 5, 6, 7 and 8 (Volume One C2D2(1) and Table C2D2).
Rise in storeys is counted where the building has the most storeys above the ground. Count at every part of the external walls, above the finished ground next to that part, take the greatest number and add any storeys in the roof space (C2D3(1)).
Two kinds of storey are left out. A top storey containing only plant, lift equipment or water tanks, and a storey partly below the ground whose ceiling is not more than 1 m above the average finished ground (C2D3(2)). Tall Class 7 and 8 storeys can count twice, and large mezzanines count once (C2D3(3) and (4)).
Effective height is a different measure. It is the distance in metres from the floor of the lowest counted storey to the floor of the topmost storey (NCC glossary). Over 25 m it brings in sprinklers throughout (E1D5), an emergency lift (E3D5) and more.
The Type changes more than FRLs. It decides non-combustible external walls (C2D10), the maximum fire compartment size (Table C3D3), spandrels between windows (C3D7) and the doors to apartments (C4D12).
1. What Type A, B and C construction are
Part C2 of Volume One grades fire-resisting construction in three Types, named by letter. Type A asks the most of a building and Type C the least: C2D4 speaks of "the most fire-resisting Type", and Specification 5 asks the highest FRLs of Type A.
The minimum Type is determined from Table C2D2 (C2D2(1)). The clause names three exceptions, covered below: certain two-storey Class 2, 3 or 9c buildings (C2D6), a Class 4 part on the top storey (C2D4(2)), and open spectator stands and indoor sports stadiums (C2D8).
Once the Type is known, each building element must comply with Specification 5 (C2D2(2)). That is where the FRLs live, in one set of tables for each Type. Our FRL guide reads those tables and has a finder for each element. This guide stays with the step before: getting the Type right.
Volume One covers Class 2 to 9 buildings (A1G1). Houses, garages and sheds (Class 1 and 10) are not given a Type. Their fire separation is in the ABCB Housing Provisions, covered in our guide to fire-rated walls for houses.
2. Table C2D2: rise in storeys against class
The whole table is eight cells. Find the rise in storeys down the side and the class across the top.
| Rise in storeys | Class 2, 3 or 9 | Class 5, 6, 7 or 8 |
|---|---|---|
| 4 or more | Type A | Type A |
| 3 | Type A | Type B |
| 2 | Type B | Type C |
| 1 | Type C | Type C |
NCC 2025 Volume One Table C2D2, Type of construction required.
The first column holds apartments (Class 2), hotels and boarding houses (Class 3) and Class 9: health care (9a), assembly buildings and schools (9b) and residential care (9c). The second holds offices (Class 5), shops (Class 6), carparks and warehouses (Class 7a and 7b) and factories and laboratories (Class 8). Our building classes guide sets out each class. At three storeys an apartment building is Type A and an office building Type B.
3. Counting the rise in storeys
The glossary defines rise in storeys as the greatest number of storeys calculated in accordance with C2D3. So the count starts with what a storey is, then follows C2D3.
What a storey is. A storey is a space between one floor level and the floor level next above or, at the top, the ceiling or roof above (NCC glossary). The definition excludes a space that contains only:
a lift shaft, stairway or meter room
a bathroom, shower room, laundry, water closet or other sanitary compartment
accommodation for not more than 3 vehicles
a combination of these.
A mezzanine is not a storey under the definition either, though C2D3(4) brings large ones back into the count. So a ground level that holds only a three-car garage and the entry stair is not a storey. Nor is a rooftop enclosure that holds only the stair and the lift shaft.
The basic count. The rise in storeys is the sum of the greatest number of storeys at any part of the external walls, and any storeys within the roof space (C2D3(1)). The storeys are counted above the finished ground next to that part of the wall. Where part of an external wall is on the boundary of the allotment, that part is counted above the natural ground level at the relevant part of the boundary instead (C2D3(1)(b)). The glossary defines finished ground level as the ground level adjacent to footing systems at the completion of construction and landscaping.
On a sloping site the parts of the wall give different numbers. A building with three storeys above the street and four at the rear has a rise in storeys of four, because the count is taken where it is greatest. A storey in the roof space, such as an attic level of apartments, is added on top.
Plant at the top. A storey is not counted if it is situated at the top of the building and contains only heating, ventilating or lift equipment, water tanks, or similar service units or equipment (C2D3(2)(a)). The word "only" carries the rule. A rooftop plant room with a communal gym beside it is a storey that counts.
The 1 m test for lower levels. A storey is not counted if it is situated partly below the finished ground and the underside of its ceiling is not more than 1 m above the average finished level of the ground at the external wall (C2D3(2)(b)). Where the external wall is more than 12 m long, the average is taken for the 12 m part where the ground is lowest. So on a sloping site a long lower level is judged on the 12 m where it is most exposed.
A basement wholly below the finished ground never enters the count. It is not above the ground at any part of the external walls, so C2D3(1) does not reach it.
Tall industrial storeys. In a Class 7 or 8 building, a storey with an average internal height of more than 6 m counts as one storey if it is the only storey above the ground, and as 2 storeys in any other case (C2D3(3)). A single-storey warehouse 10 m high stays at a rise of one. Put a level of offices over a 7 m factory floor and, reading C2D3(3) for the Class 8 storey of the building, the rise is three: two for the factory floor and one for the offices. Where the building has more than one class, confirm that reading with the certifier.
Mezzanines. The glossary defines a mezzanine as an intermediate floor within a room that is not separated from that room by walls; a solid balustrade does not count as a wall. A mezzanine is regarded as a storey in the part of the building where it sits if its floor area is more than 200 m² or more than one-third of the floor area of the room, whichever is the lesser (C2D3(4)(a)). Two or more mezzanines at or near the same level are treated as a storey if their combined area passes the same test (C2D3(4)(b)).
The one-third limit bites in small rooms. A 120 m² mezzanine in a 300 m² shop exceeds one-third of the room (100 m²), so it counts. The same mezzanine in a 2,000 m² warehouse is under both limits and does not.
4. Effective height is a different measure
The glossary defines effective height as the vertical distance between the floor of the lowest storey included in the calculation of rise in storeys and the floor of the topmost storey. A topmost storey containing only heating, ventilating, lift or other equipment, water tanks or similar service units is excluded. Four things follow from that wording:
It is a distance in metres, not a count of storeys.
It starts at the lowest storey that counts in the rise in storeys. On a sloping site that may be a lower ground level opening to the low side. Basements left out of the count are left out of the effective height too.
It ends at the floor of the topmost storey, not at its ceiling, the roof or the parapet.
A plant-only top storey is ignored, so the measure stops at the floor of the storey below it.
Rise in storeys sets the Type. Effective height switches on a separate set of provisions. These are the thresholds most projects meet:
| Effective height | What it brings in | Clause |
|---|---|---|
| More than 12 m | Stairway, floor level and sole-occupancy unit signs (also required with more than 3 below-ground storeys) | D3D31(1) |
| Lifts serving a storey above 12 m | Fire service controls; and, where no emergency lift is required, a stretcher facility in at least one passenger lift | E3D9(1), E3D3(1) |
| Not more than 25 m | Sprinklers throughout a Class 2 or 3 building with a rise in storeys of 4 or more, other than a residential care building | E1D6 |
| More than 25 m | Sprinklers throughout the whole building, with two narrow exceptions | E1D5 |
| More than 25 m | At least 2 exits from each storey (in Class 9, also at a rise in storeys of more than 6) | D2D3(2), (4) |
| More than 25 m | An emergency lift, a fire control centre and an emergency warning and intercom system | E3D5, E1D15, E4D9 |
| A storey above 25 m | Pressurisation, or open access ramps or balconies, for the fire-isolated stairways serving it | E2D4(2) |
Thresholds in NCC 2025 Volume One that turn on effective height. Each clause has conditions of its own; read it before relying on the summary.
5. More than one class, Class 4 parts and mixed Types
Buildings of multiple classification. Where a building holds more than one class, the Type is the most fire-resisting Type that Table C2D2 gives when the classification of the top storey is applied to all storeys (C2D4(1)). Where the top storey itself holds more than one class, read the table for each and take the most fire-resisting result.
The rule reads the top of the building, not the bottom. A three-storey building with a shop on the ground floor and two storeys of apartments above is read as Class 2 throughout. Rise in storeys three, Class 2 column: Type A. A three-storey building of shops alone would be Type B.
Class 4 parts. A caretaker's or manager's dwelling inside a commercial building is a Class 4 part. When it sits on the top storey, C2D4(2) looks past it. If it occupies the whole top storey, the class of the next highest storey is used. If it occupies part of the top storey, the class of the adjacent part is used. Once the Type is set, the Class 4 part takes the same FRLs and the same separating construction as a Class 2 part in that Type (C2D7).
Mixed Types. A building may be of mixed Types of construction where it is separated in accordance with C3D8 and the Type of each part is determined under C2D2 or C2D4 (C2D5). Under C3D8(2), a part separated by a fire wall may be treated as a separate building for Sections C, D and E. The fire wall must carry the greater of the adjoining parts' FRLs, extend through all storeys common to both parts and reach the underside of the roof covering. That is how a single-storey warehouse in Type C can adjoin a three-storey office block in Type B.
6. Concessions and variations that change the Type
Two-storey Class 2, 3 and 9c buildings. A building with a rise in storeys of 2 may be Type C rather than the Type B the table gives (C2D6) if either:
it is a Class 2 or 3 building, or a mixture of the two, and each sole-occupancy unit has access to at least 2 exits or its own direct access to a road or open space; or
it is a Class 9c building protected throughout with a sprinkler system complying with Specification 17 (other than an FPAA101D or FPAA101H system) and within the Table C3D3 maximum compartment size for Type C.
The first limb fits townhouse-style apartments where every unit has its own front door to the street. D2D3(2) also lists a Class 2 or 3 building subject to C2D6 among the buildings that need at least 2 exits, so check the exit layout together with the concession.
Open spectator stands and indoor sports stadiums. One may be Type C, and need not comply with the rest of Part C2, if it has not more than one tier of seating, is of non-combustible construction and has only changing rooms, sanitary facilities or the like below the seating (C2D8).
South Australia. The South Australian variation to C2D2 adds two requirements. A Class 2 building must not be built within 3 m of a Class 10b brush fence, and a brush fence must not be built within 3 m of a Class 2 building, unless any part of the building within 3 m of the fence complies with SA C3D16 (SA C2D2(3) and (4)).
7. What each Type changes beyond FRLs
The FRL tables are the obvious consequence. Our FRL guide covers them. The Type also switches these on:
Non-combustible construction, Type A and B. In a building required to be of Type A or B construction, these elements and their components must be non-combustible (C2D10(1)):
external walls and common walls, including the facade covering, framing and insulation
the flooring and floor framing of lift pits
non-loadbearing internal walls that are required to be fire-resisting.
Non-loadbearing service shafts follow in C2D10(2), and C2D10(4) to (6) list the exempt items and the materials deemed non-combustible, plasterboard and fibre-cement sheeting among them. External bonded laminated cladding panels must also have every layer mechanically supported or restrained (C2D15). None of this applies to a building of Type C, which is one reason the 1 m test and the two-storey concession matter on small projects.
Fire compartment size, Class 5 to 9. Table C3D3 caps the floor area and volume of each fire compartment by Type (C3D3(1)). A plant-only part at the top of the building is not counted in the area or volume (C3D3(2)).
| Classification | Type A | Type B | Type C |
|---|---|---|---|
| Class 5, 9b or 9c | 8,000 m² and 48,000 m³ | 5,500 m² and 33,000 m³ | 3,000 m² and 18,000 m³ |
| Class 6, 7, 8 or 9a (except patient care areas) | 5,000 m² and 30,000 m³ | 3,500 m² and 21,000 m³ | 2,000 m² and 12,000 m³ |
Maximum floor area and volume of a fire compartment or atrium, from NCC 2025 Volume One Table C3D3. Patient care areas in Class 9a are covered by C3D6; large isolated buildings by C3D4.
Spandrels, Type A. In a building of Type A construction, openings in an external wall must be separated where a window or other opening is above an opening in the storey next below and its vertical projection falls no further than 450 mm outside the lower opening, measured horizontally (C3D7(1)). The separation is a non-combustible spandrel at least 900 mm high and 600 mm above the floor, or a slab projecting at least 1100 mm and extending at least 450 mm beyond the openings, either with an FRL of 60/60/60. A building sprinklered throughout to Specification 17 (other than with an FPAA101D or FPAA101H system) is exempt, among others (C3D7(2)).
Doors to apartments. In a Class 2 or 3 building, a protected doorway from a sole-occupancy unit is at least a self-closing –/60/30 fire door in Type A. In Type B or C it is a self-closing, tight-fitting solid core door at least 35 mm thick (C4D12(4)).
Travel by open stairs. In a Class 2, 3 or 4 building, the distance from the door of a unit to the point of egress to a road or open space, by way of a required stairway or ramp that is not fire-isolated, is at most 30 m in Type C and 60 m in any other case (D2D14(2)).
One more rule turns on the rise in storeys itself rather than the Type. In a building with a rise in storeys of not more than 2, concrete external walls that could collapse as complete panels, such as tilt-up and precast panels, must comply with Specification 8 (C2D12).
8. Count the storeys and find the Type
Choose the class, then build the section: storeys above the ground, basements, a partly buried lower level, rooftop plant, a mezzanine, and for Class 7 or 8 a storey over 6 m high. The drawing shades and numbers the storeys that count, and the headline gives the Type. The cards show how each level was treated, the effective height and what the Type brings with it, each with its clause.
9. Worked examples
| Building | How the storeys count | Rise | Type |
|---|---|---|---|
| Office (Class 5) on a slope: two storeys above the street, a lower level opening to the rear, one basement, rooftop plant | The lower level's ceiling is 1.5 m above the average ground over the lowest 12 m, so it counts (C2D3(2)(b)). 1 + 2 = 3. The basement and plant do not count | 3 | B. With the ceiling at 1.0 m the rise is 2 and the Type C |
| Shop-top housing: ground-floor shop (Class 6), two storeys of apartments (Class 2) | Three storeys. The top storey is Class 2, so the Class 2 column applies to every storey (C2D4(1)) | 3 | A |
| Two-storey walk-up apartments, every unit with its own door to the street | Two storeys. Table C2D2 gives Type B, and C2D6(1)(a) allows Type C | 2 | C |
| Warehouse (Class 7b), one storey 9 m high, a 150 m² office mezzanine in a 2,000 m² room | The tall storey is the only storey above the ground: one (C2D3(3)). The mezzanine is under the lesser of 200 m² and 667 m², so it does not count (C2D3(4)) | 1 | C |
| Factory (Class 8) with a 7 m production floor and a storey of offices (Class 5) above | Reading C2D3(3) for the Class 8 floor, it counts as 2 because it is not the only storey above the ground. 2 + 1 = 3. The top storey is Class 5. Confirm the reading for a building of more than one class with the certifier | 3 | B |
| Apartments (Class 2), nine storeys over two basements, rooftop plant, 3.1 m floor to floor | Nine storeys count. Effective height is 8 × 3.1 = 24.8 m, so E1D6 requires sprinklers throughout | 9 | A |
Each row can be reproduced in the section builder above.
The first row is the case that catches people. From the street the office reads as two storeys and Type C. The rear elevation adds a storey, and the 1 m test keeps it in the count, so the building is Type B, with non-combustible external walls. Settle the test at concept stage, against the finished ground levels on the landscape plan.
10. Common mistakes
Counting from the street. The count is taken at every part of the external walls and the greatest is used (C2D3(1)). On a sloping site the low side usually decides it.
Calling every lower level a basement. A partly buried level drops out only when its ceiling is not more than 1 m above the average finished ground, over the 12 m of wall where the ground is lowest if the wall is longer (C2D3(2)(b)). A ceiling 1.1 m above that average counts.
Treating a rooftop room as plant. Only a top storey containing nothing but plant, lift equipment, water tanks or similar is left out (C2D3(2)(a)). A rooftop gym, communal room or enclosed terrace counts.
Measuring effective height to the roof. It runs from the floor of the lowest counted storey to the floor of the topmost storey (NCC glossary). Measuring to the parapet, or from a basement, overstates it and can push a design past 25 m on paper.
Using the rise in storeys for stairs. D2D4 decides when a stair must be fire-isolated by the number of consecutive storeys it connects. In a Class 2 building that is more than 3, subject to the allowance for one extra storey in D2D4(1)(b). Basements are storeys, so a stair from two basement levels to three storeys of apartments connects five, even though the rise in storeys is three.
11. Where to read the source
NCC 2025 Volume One is free to read on the NCC website. The parts used here are A1G1, Part C2 (C2D2 to C2D8, C2D10, C2D12 and C2D15) with Table C2D2, C3D3 and Table C3D3, C3D7, C3D8, C4D12, D2D3, D2D4, D2D14, D3D31, E1D5, E1D6, E1D15, E2D4, E3D3, E3D5, E3D9 and E4D9. Read them with Specification 5 and the glossary entries for storey, rise in storeys, effective height, mezzanine and finished ground level. The South Australian variation is printed with C2D2.
Inside AEC Assistant the Code text is searchable by clause. Ask whether the lower ground floor of your building counts in its rise in storeys 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.
Questions this guide answers
What is Type A, B and C construction?
They are the three Types of fire-resisting construction in NCC Volume One, Type A the most fire-resisting and Type C the least. Table C2D2 sets the minimum Type from the building's class and its rise in storeys, and each Type has its own FRL tables in Specification 5.
How do you calculate rise in storeys?
Under NCC Volume One C2D3, count the storeys above the finished ground at each part of the external walls, take the greatest number, and add any storeys within the roof space. A top storey containing only plant, lift equipment or water tanks is not counted, and nor is a storey partly below the ground whose ceiling is not more than 1 m above the average finished ground.
Does a basement count in rise in storeys?
A basement wholly below the finished ground does not count, because it is not above the ground at any part of the external walls. A level partly below the ground is left out only if the underside of its ceiling is not more than 1 m above the average finished ground at the external wall, taken over the 12 m where the ground is lowest when the wall is longer than 12 m (C2D3(2)(b)).
What is the difference between effective height and rise in storeys?
Rise in storeys is a count of storeys, and it sets the Type of construction. Effective height is a distance in metres from the floor of the lowest storey counted in the rise in storeys to the floor of the topmost storey, leaving out a top storey of plant only. Over 25 m of effective height, for example, sprinklers are required throughout the building (E1D5).
Can a two-storey apartment building be Type C construction?
Yes. Table C2D2 makes a two-storey Class 2 or 3 building Type B, but C2D6 allows Type C if each sole-occupancy unit has access to at least 2 exits or its own direct access to a road or open space. A two-storey Class 9c building may also be Type C if it is sprinklered throughout to Specification 17 (other than with an FPAA101D or FPAA101H system) and within the Type C compartment size of Table C3D3.
Does a mezzanine count as a storey?
A mezzanine counts as a storey in the part of the building where it sits when its floor area is more than 200 m² or more than one-third of the floor area of the room, whichever is the lesser (C2D3(4)). Two or more mezzanines at or near the same level are added together for the test.
