Cross-flow

Where small diameter branch waste pipes connect to a stack, they must be arranged to eliminate the risk of cross-flow.

'H' = 200mm irrespective of stack order.

To prevent cross flow from a large diameter branch to a smaller waste connection, the waste connection should be made at right angles or at least 200mm below the restricted zone.

A five boss branch may be used in some situations in preference to the collar boss but its use is dependant on the position of sanitary appliances in relation to the stack.

The Marley collar boss was specifically designed to overcome installation problems imposed by the 200mm restricted zone. It allows multiple low level bath or shower waste pipes to be connected to the stack above floor level.

Note: If you are installing a new soil stack or drainage system, or significantly altering an existing system, you will need to inform the Building Control Department at your local Council. You will need to demonstrate that the work carried out conforms to Building Regulations: England & Wales or Scotland