Allowable Building Area per Story (IBC Chapter 5)
The first feasibility number on a commercial project: how many square feet per floor the building may be, Aa = At + NS x If, where the frontage increase If = [F/P - 0.25] x W/30 rewards perimeter on open space and floors at zero below a quarter of the perimeter. The tabular areas come from Table 506.2 in the correct sprinkler column, and adding a sprinkler system can triple the area for a single-story building - the first lever a developer reaches for when the area is tight. A feasibility aid, not a code-official determination.
Formula and source
w_eff = min(open_width_ft, 30); frontage_if = (F/P) < 0.25 ? 0 : (F/P - 0.25) x (w_eff / 30); allowable = tabular_area + ns_area x frontage_if; pass = actual_area <= allowable.
IBC 2021 §506.2 (Aa = At + NS x If), §506.3.1, §506.3.2 (If = [F/P - 0.25] x W/30), and §506.3.3 (W capped at 30 ft), by name; Table 506.2 supplies the tabular areas.
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