Final answer:
The width of yards adjacent to exterior openings in buildings two stories or less above the grade plane is determined by the building code regulations.
Step-by-step explanation:
In building codes, the width of yards adjacent to exterior openings that provide natural light or ventilation is specified to ensure safety and proper functioning of the building. For buildings that are two stories or less above the grade plane, the minimum yard width is determined by the building code regulations. The specific width requirement may vary depending on the location and jurisdiction, but it is typically defined in terms of feet.