How many rows of bridging should be installed for a joist over 16' long?

For a joist that spans over 16 feet, building codes and best practices in carpentry typically recommend the installation of two rows of bridging. Bridging helps to stabilize the joists and prevent them from twisting or warping under load. This is particularly crucial for longer spans, as increased distances between supports can lead to greater movement and potential structural issues.

The two rows of bridging are usually placed at intervals that effectively distribute the weight and enhance the overall strength of the joist system. This approach helps ensure that the flooring above maintains its integrity and minimizes the risk of bounce or deflection.

While other answers suggest varying amounts of bridging, it is essential to adhere to sound engineering principles, which dictate that two rows are sufficient and appropriate for the conditions specified. Additionally, additional rows may not be necessary and could lead to unnecessary labor and material costs without providing significant benefits in this scenario.