What factor determines if a cricket is needed on a roof?

A cricket is a small, sloped section of a roof that is designed to redirect water away from a chimney or other vertical structure. The key factor in determining whether a cricket is needed is the width of the chimney. When a chimney is wider than a certain dimension, it can create a situation where water tends to pool around it, leading to potential leaks and water damage. A cricket helps to channel the water away, ensuring proper drainage run-off.

Considering the other factors, while the height of the roof, slope of the roof, and area of the roof can influence drainage and overall roof design, they do not play as critical a role in determining the need for a cricket specifically as the width of the chimney does. Each of these other factors can affect how water flows on a roof, but they are not the primary reason for implementing a cricket to manage water drainage around a chimney.