The number of stairwells is a statistic taken horizontally at any floor or level of a structure, and indicates the number of distinct areas within the plan, separate from each other, where stairways are housed and the levels are open to each other (even if certain levels are not accessible through the stairways).

If two stairways are interwoven and share the same space in a general floorplan, they are considered one stairwell. However, two stairwells can abut each other if they are completely distinct, and can be divided by a vertical plane.

Stairwells do not include stairs which rise only partway between different floor levels, or which connect different levels of uneven floors.

This field can be applied to individual floor levels according to the above definition. If it is applied to larger constructions such as buildings or complexes, then the cumulated number should treat each stairwell singly as high and as low as it can be construed as continuing. This means that a stairwell which rises from the basement to the top floor is treated as one stairwell, and furthermore if it rises disconuously or shifts its location within the plan it should still be treated singly. The cumulative number therefore expresses the maximum number of stairwells in an entity at any one floor level.