What is typically not a factor in determining the flow capacity of sewers?

The flow capacity of sewers is primarily influenced by factors that directly affect the movement of wastewater through the system. Among the options provided, the size of the connected buildings is typically not a direct factor in determining the flow capacity of sewers. Instead, it relates more to how much wastewater those buildings produce, which is not the same as the sewer's ability to handle that flow.

Pipe grade, material, and diameter are all critical elements that directly impact how efficiently and effectively wastewater travels through the sewer system. The grade of the pipe affects the flow velocity, which can influence the overall capacity. The material of the pipe can determine how smooth the interior surfaces are, affecting friction and flow resistance. Finally, the diameter of the pipe is a primary determinant in the volume of flow that can be carried at any given time.

In summary, while the size of connected buildings may influence the overall demand or contribution to flow, it does not determine the physical characteristics or capacity of the sewer system itself. Therefore, it is not considered a determining factor in the technical assessment of sewage flow capacity.