Final answer:
Open risers in staircases are forbidden by building codes due to safety concerns. Closed risers provide support and prevent accidents. Building codes also regulate the maximum gap size between treads for added safety.
Step-by-step explanation:
Open risers are the spaces between the treads of a staircase. Building codes in most areas forbid open risers because they pose a safety risk. Without a solid riser to prevent slipping through or getting a foot stuck, open risers can cause accidents. For example, a small child could fall through the gap or someone's foot could slip between the treads.
By requiring closed risers, building codes ensure that staircases are safe for everyone to use. The closed risers provide support and prevent potential hazards. Additionally, building codes often specify the maximum gap size between treads to further enhance safety.