What should always be used at the connection to roof drains?

Using an expansion joint at the connection to roof drains is essential due to the nature of the materials and the environmental conditions involved. Roof drains are often subjected to thermal expansion and contraction as temperatures fluctuate throughout the day and seasons. These movements can create stress on the piping system. An expansion joint accommodates such movements, preventing stress-related damage to the piping, such as cracking or disjointing. This ensures a more stable and durable connection, thereby enhancing the reliability of the drainage system.

Flexible pipes and unions may provide some level of adaptability or ease of maintenance, but they do not specifically address the need for accommodating thermal movement in the same way an expansion joint does. Support brackets are necessary for securing pipes but do not offer any benefits related to thermal expansion, which makes them less suitable for this specific connection.