What is the minimum length of perforated pipe recommended to prevent the membrane material from obstructing suction pipes in a sub-membrane depressurization system?

The minimum length of perforated pipe recommended in a sub-membrane depressurization system is important for ensuring that the suction pipes remain unobstructed and function effectively. A length of 3 feet helps to create sufficient spacing from the membrane material, allowing for unobstructed airflow and the effective removal of radon and other gases from beneath the membrane.

This length is considered adequate to mitigate the risk of membrane material, dirt, or debris interfering with the performance of the system. It ensures that the perforated pipe can effectively draw air and radon from the sub-membrane area without immediate contact with the membrane itself. This spacing helps in maintaining the intended pressure differential and maximizing radon extraction.

Longer lengths may provide added security but are generally not deemed necessary for effective performance, while shorter lengths could lead to complications in airflow and potential obstruction. Therefore, the recommendation for 3 feet strikes a balance between effectiveness and practicality in radon mitigation design.