‘Rise in Storeys’ – Definition of ‘Storeys’ and How to Calculate

rise-in-storeys

‘Rise in Storeys’ – Definition of ‘Storeys’ and How to Calculate

As architects and engineers, we get asked a lot of questions relating to the application of National Construction Code (NCC) through the design phase of (pharmaceutical) facilities. A common question relates to the calculation of ‘rise in storeys’. Before answering that question, it’s important to understand what is meant with the term ‘rise in storeys’ and the definition of a ‘storey’ in NCC.

What is a ‘storey’ in NCC?

Within Schedule 3 (Definitions section) the NCC states that;

Storey means a space within a building which is situated between one floor level and the floor level next above, or if there is no floor above, the ceiling or roof above, but not—

(a) a space that contains only—

(i) a lift shaft, stairway or meter room; or
(ii) a bathroom, shower room, laundry, water closet, or other sanitary compartment; or
(iii) accommodation intended for not more than 3 vehicles; or
(iv) a combination of the above; or

(b) a mezzanine.

So, in other words (or pictures) a storey can be defined in three distinct ways:

1. A storey extends from one floor level to the next floor level above, or, if it is the top storey, to the ceiling or roof above.

Figure 1: Building section
Figure 1: Building section

2. There are exceptions for some areas (such as a space containing only stairway or sanitary compartment, etc.), as they are considered to have a low level of occupancy and fire load.

Figure 2: Storeys in a building
Figure 2: Storeys in a building

3. The definition emphasizes the difference in meaning between ‘storey’ and ‘mezzanine’. Described as ‘an intermediate floor within a room’ in NCC, a ‘mezzanine’ must be within another room i.e. as a part of it. If the mezzanine is enclosed, it is regarded as a storey.

Figure 3: Enclosed floor
Figure 3: Enclosed floor

What does ‘rise in storeys’ mean?

The National Construction Code (NCC) defines the ‘rise in storeys’ as copied below:

“… the sum of the greatest number of storeys at any part of the external walls of the building and any storeys within the roof space –

i. above the finished ground next to that part; or
ii. if part of the external wall is on the boundary of the allotment, above the natural ground level at the relevant part of the boundary. “

So basically, it looks something like this:

Figure 4: Building section
Figure 4: Building section

The total number of storeys of a building often varies at different parts of external walls, so in this case we take the greatest rise and the entire building will be regarded as having a rise in storeys of that number:

Figure 5: Sum of the greatest number of storeys
Figure 5: Sum of the greatest number of storeys

Basement levels, located entirely below the ground level, are excluded when calculating rise in storeys.

Figure 6: Basement floors
Figure 6: Basement floors

What if the storey is only partly below the finished ground?

In this case, whether a storey is counted or not depends on the height between the underside of ceiling and the average finished level of ground at the external wall. If that height is more than 1m, the storey is counted, otherwise it is not.

Storeys partly below the finished ground-v2
Figure 7: Storeys partly below the finished ground

Of course the ground level may be variable, so for large buildings (having external wall longer than 12m) the average height is worked out by considering only the 12m part of the wall from the side where the ground is lowest.

Figure 8: Building on sloping site
Figure 8: Building on sloping site

As the average height of the shaded area is greater than 1m, this storey is included in the calculation of rise in storeys.

What about technical areas on the top storey?

Technical areas on the topmost storey of buildings, which accommodate only service units or equipment (such as heating, ventilating, lift equipment, water tanks, etc.) are considered to have a low level of occupancy and fire load. Therefore, they are not included when calculating the rise in storeys.

Figure 9: Technical areas on the topmost storey
Figure 9: Technical areas on the topmost storey

Class 7 or 8 buildings

Pharmaceutical manufacturing facilities are generally of class 7 and also 8 buildings. It is not unusual for these types of buildings to have higher ceilings than usual, due to the equipment and associated service provisions (tall process equipment availability, high capacity storage, etc.). If the average internal height of a single storey is more than 6m, it is counted as a single storey.

Class 7 or 8 buildings
Figure 10: Class 7 or 8 buildings

However, if there are multiple storeys, with one storey having an internal height more than 6m, then that storey is in fact counted as two.

Is Mezzanine counted?

For the purposes of calculating the rise in storeys of a building, mezzanines can be counted as a storey under some conditions.
A mezzanine is included in the calculation when the area is more than 200 m2 or more than 1/3 of the floor area of the room.

Figure 11: Mezzanine regarded as a storey

Figure 11: Mezzanine regarded as a storey
Figure 11: Mezzanine regarded as a storey

Similarly, two or more mezzanines (at or near the same level) are counted as a storey, when their aggregate floor area is more than 200 m2 or more than 1/3 of the floor area of the room.

Want more?

Designing in accordance with all of the relevant codes and standards can be somewhat complex, and should be designed and certified by licensed practitioners so please contact PharmOut if we can be of help. (See PharmOut’s services for Pharmaceutical Manufacturers for more detail.)

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