For floor joists, which of the following must be approved and engineered?

The requirement for floor joist icing to be approved and engineered stems from the need to ensure the structural integrity of the floor system in relation to various environmental conditions, particularly in wet or humid climates where ice may form. Proper engineering takes into account the potential for ice build-up which can add additional loads and stresses to the floor joists.

By requiring that floor joist icing is designed and approved, it ensures that the joists can withstand any added weight and potential damage caused by ice accumulation, thus maintaining safety and functionality. Engineering judgments consider factors like load paths, materials, and environmental influences.

The other factors like size, material, and spacing are indeed critical to the overall construction and must comply with certain codes and standards, but they do not specifically pertain to the unique challenges posed by icing. Rather, they are typically standardized or based on established guidelines, whereas the effects of icing may vary based on location and specific site conditions, necessitating a tailored engineering approach.