Every flight of stairs with four or more risers must have __________.

Step 1: Define the Problem

Identify the requirement for flights of stairs with four or more risers.

Step 2: Break Down the Problem

Determine what safety or building code feature is typically required for stairs with this number of risers.

Step 3: Apply Relevant Concepts

Consult building codes or safety standards that apply to stair construction.

Step 4: Analysis, Verify and Summarize

Analyze common building codes, such as the International Building Code (IBC), which often require handrails for stairs with four or more risers.

Final Answer

Every flight of stairs with four or more risers must have handrails.