Final answer:
The openings at guards on the sides of stair treads should not exceed 4 inches in diameter to prevent small children from slipping through, adhering to current building codes for safety.
Step-by-step explanation:
The question concerns construction safety, specifically relating to the design of stair guards. The opening at guards on the sides of stair treads should not allow the passage of a sphere that is 4 inches in diameter. This is a building code requirement meant to prevent small children from slipping through the guards on a staircase. The rule of thumb for design spacing in stair guards has evolved over time. While older guidelines suggested using 5 diameters side-to-side and 7-8 diameters deep, newer guidelines recommend as much as 8 diameters side-to-side and 15 diameters deep to ensure safety and prevent accidents. It is crucial for those involved in stair design and construction to comply with current building codes to ensure the safety of all users.