On panelized roofs, how far apart are joists hung off the purlins?

On panelized roofs, how far apart are joists hung off the purlins?

• A. 4 feet
• B. 2 feet
• C. 1 foot
• D. 3 feet

Answer: (B)

On panelized roofs, the joists are hung from the purlins at regular intervals to provide solid, evenly spaced bearing under the roof panels. The standard spacing is two feet because panelized systems typically use panels about 2 feet wide. Spacing the joists every 2 feet gives each panel edge direct support, keeps loads transferring cleanly to the purlins, and minimizes deflection. If the spacing were much larger, like four feet, the panels could sag or flex between supports. If it were much smaller, like one foot, it would add cost without adding meaningful benefit. Three feet would also misalign with the panel widths, leading to uneven support along panel edges.

On panelized roofs, the joists are hung from the purlins at regular intervals to provide solid, evenly spaced bearing under the roof panels. The standard spacing is two feet because panelized systems typically use panels about 2 feet wide. Spacing the joists every 2 feet gives each panel edge direct support, keeps loads transferring cleanly to the purlins, and minimizes deflection.

If the spacing were much larger, like four feet, the panels could sag or flex between supports. If it were much smaller, like one foot, it would add cost without adding meaningful benefit. Three feet would also misalign with the panel widths, leading to uneven support along panel edges.