The office inside a warehouse: how it changes the building

By Brenscot Builders | Last reviewed September 2026

Almost every warehouse has an office. It is usually treated as a small piece of fitout at the front of a large shed, and priced as though it were a fraction of the job.

It is not, and the reason is that the office can change the classification of part of the building. Once it does, a different set of NCC requirements applies to it, and the most expensive of those is energy efficiency.

This article refers to NCC 2022 Volume One, which applies in Queensland until NCC 2025 commences on 1 May 2027.

The short answer

A warehouse is Class 7b or Class 8. An office is Class 5. Where the office is less than 10% of the floor area of the storey it sits on, the NCC allows the classification of the rest of the storey to apply to the whole storey, and the office is simply part of the warehouse. Cross that threshold and you have a multi-classified building: fire separation between the classifications comes into play, and, far more significantly, a conditioned office creates a building envelope where an unconditioned shed had none, which brings NCC Section J requirements that did not previously apply.

The 10% rule

The NCC provides that where a part of a building has been designed, constructed or adapted for a different purpose and is less than 10% of the floor area of the storey it is situated on, the classification of the other part of the storey may apply to the whole storey.

Two details decide whether you get the benefit.

It is 10% of the storey, not of the building. In a single-storey warehouse the storey is the whole floor, so the comparison is office area against total floor area. A 400 m2 office in a 5,000 m2 shed is 8% and can be treated as part of the Class 7b or 8. The same 400 m2 office in a 3,000 m2 shed is 13%, and the office becomes Class 5 in its own right.

Some uses are excluded from the concession. It does not apply where the minor use is a laboratory, a Class 9b early childhood centre, or a Class 2, 3 or 4 part.

Where a building has more than one classification, the more stringent requirements apply to each part.

That 10% line is worth knowing at concept stage, because the difference between 9% and 11% of floor area is a design decision, and the consequences on the other side of it are not trivial.

What actually changes when the office is Class 5

Less than people expect in some areas, and more in one.

Access changes very little. The NCC's access provisions in Part D4 group Class 5, 6, 7b, 8 and 9a together for the purposes of general building access, so the office being Class 5 does not by itself change the access obligation. Access has to be provided to areas normally used by the occupants either way. This is a common misconception.

Sanitary facilities are worked out differently. The required numbers come from tables in Part F4 that differ by classification, so a Class 5 office and a Class 7b or 8 warehouse are calculated on different bases. More on this below.

Fire separation comes into play. Where different classifications sit in the same storey, the NCC addresses separating them, and the usual answer is a fire wall between the classifications, or applying the more stringent requirements to the whole. That is a real cost, and it is a cost that disappears entirely if the 10% concession applies. This is the strongest practical argument for keeping the office under the line where you reasonably can.

Energy efficiency changes the most. This deserves its own section.

Section J: the office creates an envelope where none existed

This is the point that catches even experienced people, and it is worth being precise about.

NCC Section J applies to Class 2 to 9 buildings generally. There is no blanket exemption for a warehouse. But the building fabric requirements in Part J4 apply to building elements that form part of the envelope, and the envelope is defined as separating a conditioned space or habitable room from the exterior or from a non-conditioned space.

In an unconditioned shed, the shed's own roof and walls are not an envelope, because there is no conditioned space behind them. Part J4's insulation and glazing requirements do not bite on them.

Put an air-conditioned office inside, and the office's own construction becomes the envelope. That includes the office roof or ceiling, its external walls and glazing, and the internal walls between the office and the unconditioned warehouse. Those internal walls are separating a conditioned space from a non-conditioned space, which is exactly what the definition captures.

So the insulation obligation arrives not on the big shed but on the small box inside it, including on walls that a layperson would call internal. Alongside that, the air conditioning provisions in Part J6 apply to the office's system, and the artificial lighting and power provisions in Part J7 apply across the building.

See insulation, condensation and Section J.

The practical consequence is a budget one. An office fitout priced as partitions, ceiling, carpet and a split system, without allowing for the envelope performance the Code requires, is under-priced. Getting this into the estimate at concept stage rather than at construction certificate stage is worth doing.

Sanitary facilities: the trap is the split

For a Class 7b or 8 building, the required numbers of closet pans, urinals and washbasins come from a table based on the number of employees. Where the actual number cannot be more accurately determined, the NCC directs you to calculate the population by the method used for egress.

The provision people get wrong is this one: unless the premises are used predominantly by one sex, sanitary facilities must be provided on the basis of equal numbers of males and females.

Warehouse designers routinely assume a predominantly male workforce and size the facilities accordingly. Unless you can actually establish that the premises are used predominantly by one sex, the Code requires you to assume a 50/50 split, and the female provision runs on a tighter ratio than the male provision at the lower end. A unisex accessible facility may be counted once for each sex, which helps.

If the office is separately classified as Class 5, its facilities are worked out on the Class 5 table rather than the warehouse one.

Mezzanine offices

Putting the office on a mezzanine is a common way to keep floor area in the warehouse, and it interacts with the rise in storeys rules.

Under clause C2D3, a mezzanine is regarded as a storey in the part of the building where it is situated 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.

The "whichever is the lesser" is the part that bites. In a 450 m2 room the governing limit is 150 m2, not 200 m2. Trip it and the rise in storeys increases, which can change the required type of construction under Table C2D2, and with it the fire resistance levels for the whole building. See construction Types A, B and C.

There is no NCC clause dealing specifically with egress from a mezzanine. The general provisions in Part D2 apply: the number of exits required, travel distances, and the treatment of a stairway that is not a required exit.

The consequences are larger than they look in a warehouse over 6 m average internal height, and access to a staffed mezzanine is governed by a separate test again. Both are set out in the 200 m2 mezzanine rule and warehouse access.

Designing the office well

Compliance aside, the office is the part of the building people actually experience, and in an industrial building it is usually the part that gets least design attention.

Things worth deciding early rather than late:

Frequently asked questions

Is the office in a warehouse classified separately?

It depends on size. Where the office is less than 10% of the floor area of the storey it is on, the NCC allows the warehouse classification to apply to the whole storey. Above that, the office is Class 5 and the building is multi-classified.

Does the 10 per cent rule apply to the building or the storey?

The storey. In a single-storey warehouse that is the whole floor area, so the comparison is office area against total building floor area.

Does Section J apply to a warehouse?

Section J applies to Class 2 to 9 buildings, and there is no blanket warehouse exemption. But the building fabric requirements apply to the envelope, which separates conditioned space from unconditioned space or the exterior. An unconditioned shed has no envelope. Adding a conditioned office creates one, including the walls between the office and the warehouse.

How many toilets does a warehouse need?

The numbers come from an NCC table based on employee numbers, calculated by the egress population method where actual numbers are not known. Unless the premises are used predominantly by one sex, facilities must be provided assuming equal numbers of males and females.

Can I put the office on a mezzanine?

Yes, but the mezzanine counts as a storey if its area exceeds 200 m2 or one third of the floor area of the room, whichever is the lesser. That can change the rise in storeys and therefore the required type of construction.

Sources

General information only

This article is general information, current as at September 2026. It is not building certification or energy efficiency advice. Classification, fire separation and Section J compliance for a particular building must be confirmed by your building certifier and the relevant consultants.

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