Principal | Building Codes
Principal | Building Codes
One of the more common questions we encounter during design reviews is deceptively simple:
“Is this space actually an atrium?”
The answer matters.
If a space is considered an atrium under NCC 2022 Volume One, Part G3 may apply, potentially triggering additional fire safety measures that can have a significant impact on the design, construction and operation of a building.
The challenge is that not every vertical void, courtyard, or open volume is automatically an atrium.
The NCC defines an atrium as a space within a building that connects two or more storeys and is enclosed at the top by a floor or roof.
Importantly, the NCC goes on to state that a space is considered enclosed if the area of the enclosing floor or roof is greater than 50% of the area of the space, measured in plan.
This is where many projects run into difficulty.
Too often, the assessment becomes focused on sections, elevations or visual impressions of enclosure. The NCC is actually asking a much simpler question:
Does the enclosing element cover more than 50% of the space when measured in plan?
If the answer is yes, the space may be considered enclosed at the top.
If the answer is no, it may not meet the definition of an atrium.
Before applying the 50% test, it is important to determine whether the space is actually located within the building.
An external courtyard open to the sky is generally less likely to be considered an atrium. Conversely, an internal void surrounded by conditioned spaces is far more likely to satisfy this aspect of the definition.
In practice, considerations such as weatherproofing, building enclosure and how the space functions often assist in determining whether the space forms part of the building or remains genuinely external.
Even if the space considered not within the building, if there is a number of storeys and external walkways associated with the space, the space would not be deemed an atrium, however we may need to consider the external void as a special hazard under E1D17 and E2D21.
Example of a space which would not be deemed an atrium but could be flagged as a hazard under E1D17 and E2D21.
The assessment should be undertaken in the plan if the space is deemed as being contained within the building.
This means measuring:
The following formula can then be applied:
Enclosed Percentage = Enclosing Area ÷ Space Area × 100
The result must be greater than 50%.
Exactly 50% does not satisfy the definition.
Where the shape of the void changes between stores, each level should be assessed independently.
While every project requires its own assessment, common examples include:
The key consideration is whether the element genuinely functions as an enclosure to the space when measured in plan.
Areas to consider in calculation
The classification of a space as an atrium can have significant implications for:
Getting the answer wrong can result in unnecessary fire engineering, redesigning, and additional project costs. Equally, dismissing a space as “not an atrium” can create compliance challenges later in the approval process.
When assessing whether a space is an atrium, there are two critical questions:
Is the space within the building?
Is it enclosed at the top by more than 50% when measured in plan?
While the calculation itself is relatively straightforward, the interpretation of the space and the extent of enclosure often require careful consideration.
Like many aspects of the NCC, the answer is rarely found by looking at a single drawing in isolation. It comes from understanding how the space functions, how it is enclosed and how the definition applies to the building as a whole.
Sometimes the difference between a void and an atrium is only a few square meters. The consequences, however, can be much larger.
Ellie is the powerhouse behind DC Partnership’s financial, operational and people performance. With over a decade of experience in consultancies, startups and corporate environments, she’s a master at combining big-picture strategy with hands-on problem-solving. Since joining DC Partnership in 2021, Ellie has streamlined operations, expanded the company’s footprint and kept everything running smoother than ever. A champion of diversity, inclusion and female leadership, Ellie is all about creating a workplace where everyone feels valued—and where no challenge is too big to tackle.
