The 200 m2 mezzanine rule, and what access is required if you exceed it

By Brenscot Builders | Last reviewed September 2026

Ask anyone who builds warehouses why the office is kept to 200 m2 and you will get the right answer for slightly the wrong reason. The 200 m2 figure is real and it is in the Code, but it is not an office rule, it is a mezzanine rule, it has a second limb that bites first on most buildings, and the consequences of crossing it are much larger in a tall warehouse than in a short one.

This article sets out what the rule actually says, what happens when a building goes past it, and what access has to be provided either way — because access is governed by a different test entirely, and that is where most people get caught.

The short answer

A mezzanine is counted as a storey when its floor area is more than 200 m2 or more than one third of the floor area of the room it sits in, whichever is the lesser. In most warehouses the one-third test binds well below 200 m2. Crossing the threshold increases the rise in storeys, and in a warehouse with an average internal height over 6 m that can push the building from a rise of one to a rise of three, which changes the required type of construction from Type C to Type B. That is the real reason the office is kept small.

Access is separate. In a Class 5, 6, 7b, 8 or 9a building, access must be provided to and within all areas normally used by the occupants. A staffed mezzanine office is such an area whether or not it counts as a storey.

What the rule actually says

Clause C2D3(4) of NCC 2022 Volume One, for the purposes of calculating the rise in storeys:

a mezzanine is regarded as a storey in that part of the building in which it is situated if its floor area is more than 200 m2 or more than ⅓ of the floor area of the room, whichever is the lesser

And the second limb, which people forget:

two or more mezzanines are regarded as a storey in that part of the building in which they are situated if they are at or near the same level and have an aggregate floor area more than 200 m2 or more than ⅓ of the floor area of the room, whichever is the lesser

Three things follow from that wording.

"Whichever is the lesser" means the one-third test usually governs. In a warehouse with a 600 m2 clear-span area, one third is 200 m2 and the two tests coincide. Below that, the one-third test is the binding one. In a 900 m2 room, one third is 300 m2, so the 200 m2 cap governs. Work out both numbers for your actual building rather than assuming 200 m2 is the answer.

It is one third of the room, not of the building. The relevant denominator is the floor area of the room the mezzanine sits in. In a building divided into tenancies or separated by walls, the room may be considerably smaller than the building.

Two mezzanines at or near the same level aggregate. Putting a 150 m2 office mezzanine at one end and a 120 m2 storage mezzanine at the other does not avoid the rule. They are added together.

Why crossing it matters: the tall-warehouse cliff

This is the part that makes the difference on a modern industrial building, and it comes from reading two clauses together.

Clause C2D3(3) says that in a Class 7 or 8 building, a storey with an average internal height of more than 6 m is counted as one storey if it is the only storey above the ground, or two storeys in any other case.

Most contemporary warehouses have an average internal height over 6 m. So long as the warehouse floor is the only storey above ground, it counts as one storey, and Table C2D2 gives a Class 5, 6, 7 or 8 building with a rise in storeys of one a minimum of Type C construction, the least onerous.

Introduce a mezzanine that exceeds the C2D3(4) threshold and it is regarded as a storey. The warehouse floor is then no longer the only storey above the ground, so under C2D3(3) it counts as two. Add the mezzanine and the rise in storeys becomes three. Table C2D2 requires Type B construction at a rise of three for a Class 5, 6, 7 or 8 building.

That is the cliff. Not one step, but two at once, and it lands on a different type of construction with materially higher fire resistance levels for the structure and the external walls. See Type A, B and C construction.

By contrast, in a warehouse under 6 m average internal height, an oversized mezzanine takes the rise in storeys from one to two — and Table C2D2 still gives Type C at a rise of two for these classes. Same rule, much smaller consequence. This is why the 200 m2 habit is strongest among people who build tall warehouses, and why it matters less on low-clearance buildings.

Because this consequence turns on how the two clauses interact for your specific building, confirm the rise in storeys with your building certifier before the structure is designed, not after.

The advantages of keeping it under

Staying below the threshold is not about avoiding paperwork. The gains are concrete:

• Type C construction instead of Type B, in a tall warehouse. Lower fire resistance levels on the primary structure and external walls, which flows into steel sizing, protection and cost.
• A simpler fire engineering position. Fewer interacting requirements and fewer places where a performance solution becomes the only way through.
• A shorter, more predictable certification path. The building is assessed against the requirements most single-storey industrial buildings are assessed against, which is well-trodden ground for certifiers.
• Flexibility later. A mezzanine sized comfortably under the threshold leaves room for a future occupier to add a modest amount without triggering a reassessment of the whole building.

The cost of staying under is that the office is smaller. For most industrial occupiers that is not a real constraint — the office is a small part of the operation and the warehouse floor is the asset. Where a business genuinely needs a large office, the honest answer is usually to design it as a two-storey office structure from the start, assessed properly, rather than to stretch a mezzanine to its limit.

Access: a different test, and the one people miss

Nothing above is about accessibility. Access is governed by Part D4, and the test is not floor area.

In a Class 5, 6, 7b, 8 or 9a building, access must be provided to and within all areas normally used by the occupants. A mezzanine office where staff work is an area normally used by occupants. So is a staffed mezzanine amenities area or meeting room.

The exemptions in D4D5 are narrow. Only three things are not required to be accessible: an area where access would be inappropriate because of the particular purpose for which the area is used; an area that would pose a health or safety risk for people with a disability; and a path of travel providing access only to one of those areas. There is no general exemption for upper levels, for small buildings, or for industrial buildings.

In practice that means a staffed mezzanine will generally need a compliant passenger lift or a ramp complying with AS 1428.1, and it needs to be resolved at design stage. A lift shaft is not something to discover after the slab is poured, and a compliant ramp to a mezzanine consumes a surprising amount of warehouse floor.

Where a mezzanine genuinely is used only for storage — no workstations, no staff amenities, reached by a ladder or a stair for occasional access — the position is different, and the "inappropriate because of the particular purpose" exemption may be the basis for it. That is a judgement for the certifier on the specific design. Do not assume it; get it in writing before you rely on it.

The other Part D4 requirements apply regardless of the mezzanine. Accessible carparking is required at one space per 100 spaces or part thereof for a Class 5, 7b or 8 building, and the access provisions reference AS 1428.1:2021 under NCC 2022 Amendment 2. See parking, access and amenities.

What else changes if the mezzanine becomes a storey

Beyond the type of construction and access:

• Egress. The mezzanine becomes a storey with its own requirements for exits, travel distances and stair construction under Part D2 and Part D3. On a large mezzanine this can mean a second stair in a location that suits the Code rather than the layout.
• Fire services. Coverage requirements for hose reels and extinguishers, plus exit signage and emergency lighting, apply to the new storey. See fire services.
• Sanitary facilities. Amenities provision is assessed on the building's occupancy, calculated on the basis of equal numbers of males and females unless the premises are used predominantly by one sex.
• Energy efficiency. A conditioned mezzanine office creates a building envelope, including the walls and floor separating it from the unconditioned warehouse. See insulation, condensation and Section J.

And the separate 10 per cent rule

The 200 m2 mezzanine rule is often confused with a different threshold that applies to classification. Under A6G1, where a part of a building designed for a different purpose is less than 10% of the floor area of the storey it is situated on, the classification of the other part of that storey may apply to the whole storey. That concession does not apply where the minor use is a laboratory, a Class 9b early childhood centre, or a Class 2, 3 or 4 part.

Two different tests, two different denominators, two different consequences. The mezzanine rule affects rise in storeys and therefore fire resistance. The 10% rule affects classification. A building can pass one and fail the other. See the office inside a warehouse and building classifications explained.

There is usually a planning limb as well. Local planning schemes commonly treat office floor area as ancillary to the industrial use, and an office beyond what is genuinely ancillary can change how the use is assessed. Have the planner check that alongside the Code position.

Frequently asked questions

Why is a warehouse office usually limited to 200 m2?

Because of NCC clause C2D3(4): a mezzanine counts as a storey once its floor area exceeds 200 m2 or one third of the floor area of the room it sits in, whichever is the lesser. Counting as a storey increases the rise in storeys, which in a warehouse over 6 m average internal height can push the building to a rise of three and require Type B construction instead of Type C.

Is the limit 200 m2 or one third?

Whichever is the lesser, for the specific building. In a room of 600 m2 the two are the same. Below 600 m2 the one-third test governs; above it, the 200 m2 cap does.

Can I build two smaller mezzanines to stay under?

No. Two or more mezzanines at or near the same level are assessed on their aggregate floor area against the same threshold.

Does a ground-floor office count towards the 200 m2?

No. C2D3(4) is about mezzanines and the rise in storeys. A ground-floor office is caught by the separate 10% of the storey classification concession in A6G1, not by this rule.

Do I need a lift to my mezzanine office?

If the mezzanine is an area normally used by the occupants of a Class 5, 6, 7b, 8 or 9a building, access must be provided to and within it, which generally means a compliant passenger lift or an AS 1428.1 ramp. The exemptions in D4D5 are narrow and are a matter for the building certifier on the specific design.

What if the mezzanine is only used for storage?

That is the case where the "access would be inappropriate because of the particular purpose" exemption may apply. It is a certifier's judgement on the actual design and intended use, so obtain it in writing rather than assuming it.

Can I add a mezzanine to an existing warehouse?

Often, but it is building work requiring approval, and it may change the rise in storeys, the type of construction, the egress provisions and the access obligations for the building as a whole. Have a certifier and a structural engineer assess it before committing, including whether the existing slab and frame can carry it.

Sources

• National Construction Code 2022 Volume One, C2D2 and Table C2D2: type of construction required by rise in storeys and class of building
• National Construction Code 2022 Volume One, C2D3: calculation of rise in storeys, including C2D3(3) for Class 7 and 8 storeys over 6 m average internal height and C2D3(4) for mezzanines
• National Construction Code 2022 Volume One, A6G1: determining a building classification, including the 10% of a storey exemption and its limitations
• National Construction Code 2022 Volume One, D4D2: general building access requirements, including access to and within all areas normally used by the occupants in Class 5, 6, 7b, 8 and 9a buildings
• National Construction Code 2022 Volume One, D4D5: exemptions from accessibility
• National Construction Code 2022 Volume One, D4D6: accessible carparking
• National Construction Code 2022 Volume One, Part D2 and Part D3 (egress), Part F4 (sanitary facilities), Section J (energy efficiency)
• AS 1428.1:2021 Design for access and mobility, as referenced by NCC 2022 Amendment 2

General information only

This article is general information, current as at September 2026, and summarises the Code rather than reproducing it. How the rise in storeys, type of construction and access provisions apply depends on the specific building, its height, its classification and its intended use. Confirm all of it with a registered building certifier before design is finalised.

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