When is a storey not counted in the Rise in Storeys under C1.2 (b)?
The calculation of the Rise in Storeys (RIS) typically determines the Type of Construction required (notwithstanding the provisions of NCC Clause C2.2)
The calculation in the RIS triggers an array of NCC Deemed-to-Satisfy requirements such as when sprinklers are required for a Class 2/3 building, when NCC Clause D1.18 becomes applicable for an early learning childcare centre and it is also used to calculated Effective Height of a building.
When calculating the RIS, there can be a lot of moving parts, the application of which has widespread connotations on how the building may need to be constructed.
Let’s look at when a storey is not counted in the RIS, as per the provisions of NCC Clause C1.2(b);
A storey is not counted if—
(i) 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; or
(ii) it is situated partly below the finished ground and the underside of the ceiling is not more than 1 m above the average finished level of the ground at the external wall, or if the external wall is more than 12 m long, the average for the 12 m part where the ground is lowest.
However, should a common corridor and/or an enclosed lift lobby be included at the uppermost level along with the above-mentioned exempted items, it is then considered a Storey for the purposes for calculating the RIS.
The above-mentioned scenario commonly occurs when a lift is provided to a shared roof terrace area in a multi-residential building or if your local bar fancies a bit of a beer garden/open area at the upper most level.
In this scenario an enclosed lift lobby is usually proposed in order to weatherproof the lift shaft and prevent the ingress of water; usually a good idea to prevent the electrical lift motor from getting a bit too soggy. At times we see strata committees lodging DAs for a lift lobby because they have had to replace the lift motor in the past; unknowing that the very reason for the poor design in the first place was to reduce the effective height in order to avoid the requirement of installing an expensive essential fire service.
In this instance, the provision of an enclosed lobby at this part in turn generally leads to an increase in the RIS and an increase in the Effective Height.
Moving on, the provisions of C1.2(b)(ii) permit the exclusion of a Storey from the calculation in the RIS in the scenario that:
C1.2(b)(ii) Part One;
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- The storey is situated partly below finished ground and the underside of the ceiling is not more than 1 m above the average finished level of the ground at the external wall.
A Storey is counted in the RIS when the underside of the ceiling of the Storey is greater than 1m above the average ground level at the external wall at that part.
For example, if the Storey is partly below ground, with an external wall of 6m long. We firstly take the average finished ground level at the external wall, then we measure the height to the underside of the ceiling; if it is greater than 1m, then the Storey is counted in the Rise in Storeys.
This is generally the case for below ground carpark entry at which the opening, directly to the lower ground level, is situated at the external wall.
More often than not, openings to a below ground carpark do not gain an exemption not to be counted in the RIS.
There is a common misconception that a below ground carpark with an external wall of less than 12m is not counted in the RIS.
This is not the case, when we read the words within C1.2(b)(ii), note the use of ‘or’, which implies that we only default to the 12m rule when the external wall at this part is greater than 12m in length.
So what is the 12m rule and how do we apply it?
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- A Storey is counted in the RIS if the external wall is more than 12 m long, and the ceiling height (average for the 12 m part where the ground is lowest) is less than 1 m above the average finished level of the ground.
So, a partly below ground Storey with an external wall of greater than 12m in length is counted in the RIS when the average height to the underside of the ceiling (measured at the 12m section of the external at which the ground level is at its lowest) is greater than 1m above the average height of the finished ground level at the external face of the external wall.
As always, we are available to assist with any question you may have.
Please call 02 9281 8555 or email info@credwell.com.au