Roof drains have strainer extending not less than _______ inches above the surface of the roof immediately adjacent to the roof drain.

The requirement for roof drains to have a strainer extending not less than 4 inches above the surface of the roof immediately adjacent to the roof drain is based on the need for effective water drainage and to prevent debris from clogging the drainage system. Having the strainer elevated adequately helps ensure that water can flow freely into the drain and avoids the potential for overflow or pooling of water on the roof, which can lead to structural damage or leaks.

In addition, the specified height helps prevent larger debris and items from entering the drainage system, which could cause blockages. This height is a standard practice within plumbing codes to ensure the reliability of the drainage system and maintain the safety and integrity of the roofing structure. Therefore, the choice of 4 inches is aligned with established plumbing standards and best practices in building design.