Construction Types A, B and C: how they shape warehouse design
By Brenscot Builders | Last reviewed September 2026
Every commercial building in Australia (Class 2 to 9 under the code) is assigned a type of construction under the National Construction Code (NCC): Type A, Type B or Type C. The type sets how fire-resistant the building's walls, columns and other elements must be. For a warehouse it also sets something owners care about more: how big the building can be before it has to be divided by fire walls or protected in some other way.
This article explains how the type is determined for a warehouse, what each type allows, and why it needs to be settled at concept stage.
This article refers to NCC 2022 Volume One, which applies in Queensland until NCC 2025 commences on 1 May 2027. Clause numbers are from NCC 2022.
The short answer
Most single-storey warehouses are Type C construction, the least demanding type. Type C has the lowest fire-resistance requirements but also the smallest permitted fire compartment: 2,000 m2 of floor area and 12,000 m3 of volume for a Class 7 or 8 building. A warehouse larger than that needs fire walls, a higher type of construction, the "large isolated building" provisions or a performance solution.
First, what class is a warehouse?
The NCC classifies buildings by use:
- Class 7b: a building used for storage, or for the display of goods for wholesale sale. Most warehouses are Class 7b.
- Class 8: a building where goods are produced, assembled, altered, repaired, packed, finished or cleaned for sale. Factories and workshops are Class 8.
- Class 5: an office.
A warehouse with an office is usually a mixed-classification building: Class 7b or 8 with a Class 5 part. There is a concession where a part with a different use takes up no more than 10% of the floor area of the storey it is on. In that case the minor part can generally take the classification of the main use. The concession does not apply to laboratories or residential parts. Your building certifier makes this determination.
How the type of construction is determined
Under NCC clause C2D2 and Table C2D2, the minimum type of construction depends on the building's class and its rise in storeys.
| Rise in storeys | Class 5, 6, 7 and 8 buildings |
|---|---|
| 1 | Type C |
| 2 | Type C |
| 3 | Type B |
| 4 or more | Type A |
Type A is the most fire-resistant and Type C the least. A designer can always choose a higher type than the minimum.
How rise in storeys is counted for a warehouse
Rise in storeys is the greatest number of storeys at any part of the building's external walls above ground level, plus any storeys within the roof space. Two rules in clause C2D3 matter for warehouses:
- High 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 ground, and as two storeys in any other case. A single-storey warehouse taller than 6 m still has a rise in storeys of one.
- Mezzanines. A mezzanine counts as a storey if its floor area is more than 200 m2, or more than one third of the floor area of the room it is in, whichever is less.
These two rules can interact. If a warehouse storey more than 6 m high also contains a mezzanine large enough to count as a storey, the high storey may no longer be "the only storey above ground". Depending on how the certifier applies clause C2D3, the rise in storeys could then be counted as more than two, which would require Type B construction. The NCC and the Australian Building Codes Board's guide do not give a worked example of this case. Keeping the mezzanine within the limit avoids the question. Otherwise, have the certifier confirm the storey count before fixing the mezzanine size.
What each type allows: fire compartment size
Table C3D3 sets the maximum size of a fire compartment. A fire compartment is the whole building, or a part separated from the rest by fire-resisting construction.
| Classification | Type A | Type B | Type C |
|---|---|---|---|
| Class 6, 7, 8 (warehouses, factories, shops) | 5,000 m2 and 30,000 m3 | 3,500 m2 and 21,000 m3 | 2,000 m2 and 12,000 m3 |
| Class 5 (offices) | 8,000 m2 and 48,000 m3 | 5,500 m2 and 33,000 m3 | 3,000 m2 and 18,000 m3 |
Both limits apply. Exceeding either the floor area or the volume means the compartment is too large.
Why volume usually governs
Divide the Type C limits and you get 12,000 m3 divided by 2,000 m2, which is 6 m. If the average internal height of a Type C warehouse is more than 6 m, the volume limit is reached before the floor area limit.
Worked example: a warehouse with an average internal height of 9 m reaches 12,000 m3 at about 1,333 m2 of floor area (12,000 divided by 9). The 2,000 m2 floor area allowance is never reached. In a normal warehouse, where the compartment extends up to the roof, volume is measured to the underside of the roof sheeting. The space between the rafters and the roof counts, so use the average height to the roof sheeting, not the clear height under the rafters.
This is the single most useful calculation to do at concept stage, and it is why building height should never be fixed without checking it.
What each type requires: fire resistance
The fire-resistance requirements are in NCC Specification 5, expressed as a fire resistance level (FRL): three numbers giving the minutes of structural adequacy, integrity and insulation an element must achieve in a standard fire test. For a single-storey Type C warehouse (Class 7b or 8), the key points are:
| Element | Requirement |
|---|---|
| External wall less than 1.5 m from a fire-source feature | FRL 90/90/90 |
| External wall 1.5 m to less than 3 m from a fire-source feature | FRL 60/60/60 |
| External wall 3 m or more from a fire-source feature | No FRL required |
| Roof | No FRL required |
| Fire walls | FRL 90/90/90 |
A fire-source feature is a side or rear boundary, the far boundary of an adjoining road (or river or lake), or the external wall of another building on the same site, other than a minor Class 10 structure such as a shed.
In Type A and B construction the requirements are much higher. Fire walls in Class 7b and 8 buildings must achieve FRL 240/240/240, external walls must be non-combustible (clause C2D10), and loadbearing elements need FRLs of up to 240 minutes depending on their distance from the boundary. Steel columns and other loadbearing elements may need fire protection that a Type C building avoids. That is why moving to a higher type to gain compartment size is rarely a simple trade.
Your options when the building exceeds the Type C limits
- Divide the building with fire walls so that each compartment is within 2,000 m2 and 12,000 m3. This is the natural solution for multi-unit buildings, where the walls sit on the unit boundaries. See fire walls and fire compartments.
- Adopt Type B or Type A construction to use the larger limits, accepting the higher fire-resistance requirements.
- Use the large isolated building provisions in clause C3D4. A Class 7 or 8 building of up to 18,000 m2 and 108,000 m3, with no more than two storeys, can be a single compartment if it has open space at least 18 m wide around it, kept clear of buildings and storage and including fire truck access. Alternatively it can be sprinklered throughout with perimeter vehicle access. Larger buildings need sprinklers and perimeter access. Smoke hazard management requirements also apply.
- Use a performance solution prepared by a fire engineer. This is assessed by the certifier and referred to Queensland Fire and Rescue for advice.
Each option has cost, site area and programme consequences, which is why the decision belongs at concept stage.
What this means for your project
- Fix the building height only after checking the volume calculation
- Decide early whether the building is one compartment or several
- Keep mezzanines within the storey-count limits unless there is a reason not to
- Choose the wall system with boundary distances in mind. See wall systems compared
- Remember that awnings can add to floor area and volume. See awnings and fire compartment volume
Frequently asked questions
What type of construction is a typical warehouse?
A single-storey Class 7b or Class 8 warehouse is Type C under NCC Table C2D2, unless the designer chooses a higher type.
What is the maximum size of a Type C warehouse?
A single fire compartment is limited to 2,000 m2 of floor area and 12,000 m3 of volume. A larger building is possible using fire walls, a higher type of construction, the large isolated building provisions or a performance solution.
Does a mezzanine count as a storey?
It does if its floor area is more than 200 m2 or more than one third of the floor area of the room, whichever is less.
What is the difference between Type A and Type C construction?
Type A requires the highest fire resistance and allows the largest fire compartments. Type C requires the least fire resistance and allows the smallest. Type B sits between them.
Does NCC 2025 change any of this?
NCC 2025 commences in Queensland on 1 May 2027. Until then NCC 2022 applies. Check with your certifier which edition applies to your project, because it generally depends on when the building application is made.
Sources
- National Construction Code 2022, Volume One, Australian Building Codes Board, ncc.abcb.gov.au: Part A6 (classification); clause C2D2 and Table C2D2; clause C2D3; clause C2D10; clause C3D3 and Table C3D3; clause C3D4; Specification 5; Schedule 1 definitions
- ABCB, Understanding the NCC: Building classifications
- Queensland Government, Building and Plumbing Newsflash 638 (NCC 2025 commencement in Queensland)
General information only
This article is general information based on NCC 2022 Volume One, current as at September 2026. It is not design or certification advice. Classification, type of construction and compartment size for your building must be confirmed by your building certifier and, where relevant, a fire engineer.
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