For dissimilar fixtures to be duel vented, what must be true?

In order for dissimilar fixtures to be duel vented, they must be at the same elevation. This requirement ensures that the flow of wastewater from each fixture does not interfere with the proper venting and air pressure balance needed for drainage. When fixtures are at the same elevation, it helps to create a consistent flow path that allows for effective venting, which in turn helps prevent traps from being siphoned and ensures that the drainage system functions correctly.

Choosing fixtures of the same type or requiring them to be connected by a single pipe is not necessary for duel venting. Additionally, having fixtures located in separate rooms would not affect their ability to be duel vented. Thus, the elevation is a critical factor since it directly impacts the hydraulic conditions within the drainage system and is key to the proper venting of dissimilar fixtures.