How to Calculate Stair Area

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For many legal purposes, stair area is included in the overall floor area of the building.
For many legal purposes, stair area is included in the overall floor area of the building. (Image: Digital Vision./Digital Vision/Getty Images)

When designing a new building, or seeking planning permission it is often necessary to specify the total floor area of the building. Additionally, real estate agents are required to ascertain the square footage of properties they offer for sale. In all these situations, stairs are included as "living space" and the area they occupy must be measured. Apart from determining the relevant legal definition of stair area, the process is straightforward.

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Ascertain whether the stair area measurement relates to the floor from which the stairs descend or the floor from which the stairs ascend. If the stair area is measured as part of the floor area from which they descend, the total area cannot exceed that of the gap in the floor. Thus, for example, if the stairs descend from the first floor via a hole measuring 50 square feet, but they cover 80 square feet on the ground floor, the stair area that counts towards the first floor is only 50 square feet.

Measure the length and width of either the hole through which the stairs descend or the area covered by the bottom of the stairs. Multiply the length by the width to ascertain the square footage of rectangular areas. For a spiral staircase use the formula area = pi x radius squared, where pi is usually given as 3.1415.

Treat stairs that have an "L" shape as two rectangles and calculate the length and width of each. Combine the areas to ascertain the total stair area.

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