Holes through a joist should be limited to the center third of the joist. If cut incorrectly, what happens?

Holes through a joist should be limited to the center third of the joist. If cut incorrectly, what happens?

• A. They weaken the building's entire structure
• B. They strengthen the structure
• C. They have no effect
• D. They improve insulation

Answer: (A)

Holes in a joist affect its bending strength. A joist carries loads by bending, with the outer fibers (top and bottom edges) experiencing the greatest tensile and compressive stresses. By keeping holes in the center third, you avoid removing material from those high-stress outer fibers, preserving most of the joist’s strength while still letting you pass utilities. If a hole is cut outside that center zone (too close to the top or bottom edges, or too large), you remove material from the parts of the section that carry the most stress. That weakens the joist’s ability to carry loads, leading to sagging, cracking, or even failure of the floor system. Holes do not strengthen the structure, nor do they improve insulation or have no effect.

Holes in a joist affect its bending strength. A joist carries loads by bending, with the outer fibers (top and bottom edges) experiencing the greatest tensile and compressive stresses. By keeping holes in the center third, you avoid removing material from those high-stress outer fibers, preserving most of the joist’s strength while still letting you pass utilities.

If a hole is cut outside that center zone (too close to the top or bottom edges, or too large), you remove material from the parts of the section that carry the most stress. That weakens the joist’s ability to carry loads, leading to sagging, cracking, or even failure of the floor system. Holes do not strengthen the structure, nor do they improve insulation or have no effect.