Which factor has the least effect on the deflection of a dimension lumber floor system?

The deflection of a dimension lumber floor system is primarily influenced by factors such as the joist grade, species, and spacing. Joist grade reflects the quality and strength of the lumber, significantly affecting its ability to bear loads without excessive sagging. Similarly, joist species plays a crucial role because different wood species have varying strengths and stiffness properties, impacting their performance under load. Joist spacing also directly affects deflection, as closer spacings distribute the load more effectively and reduce deflection compared to wider spacings.

In contrast, the width of the joist has a comparatively minimal impact on deflection. While wider joists can increase the surface area and may provide some slight improvements in load distribution, the predominant factors affecting deflection are the mechanical properties (grade and species) and how the joists are arranged (spacing). Therefore, the joist width does not influence deflection to the same extent as the other factors, making it the least impactful in this context.