Sanitary Piping Best Practices 2

Our last post was on understanding sanitary piping covered tracks. This week we will discuss branch discharge pipes and their role in the plumbing system.

Branch Discharge Pipes

Plumbing appliances such as toilets, showers and sinks connect to the primary drainage pipes through branch discharge pipes. These pipes are simply smaller drainage pipes feeding into a larger pipe similar to tributary streams flowing into a river. The small pipes branch out from the larger and carry the discharge from appliances; hence the name.

Thus, after the water from your appliance has passed the trap, the piping it flows through is known as the branch discharge pipe. The larger pipe is known as the discharge stack and it is possible for waste fluid to travel through multiple layers of branch pipes before reaching the final discharge stack.

Stub Stacks

Stub stacks are a variation of discharge stacks that are far shorted, often unvented (discharge stacks must always be vented) and are used to connect a group of close appliances on the ground floor of a building.

Soil Stacks

Soil stacks are just any pipes that transport waste water from the upstairs plumbing system of a building to lower floors.

Installing Branch Discharge Pipes

  • First, you must choose a branch pipe that is at least the same diameter as the appliance trap. If more than one appliance is connected to the branch pipe and there is no ventilation, the diameter must meet additional specifications as listed below.
    • For up to eight wc’s, the minimum size of the branch discharge pipe must be 100 mm.
    • For up to five urinal bowls or up to four washbasins the minimum size of the pipe is 50 mm.
    • For up to size urinal stalls the minimum size of the pipe is 50 mm.
  • It is important when installing pipes to ensure that all bends are as large as possible, with a minimum centre line radius of 75 mm. You can calculate the centre line radius by measuring two key lengths:
    • The distance between the two end points of the bend. Call this measurement A.
    • The distance from the centre of the bend to the line from each end point of the bend (ie. the other measurement line). Call this measurement B.
    • The radius is equal to: (B² + A²)/2A
  • The angle between branch discharge pipe junctions should either be 45 degrees or have a minimum sweep of at least 25 mm radius. A sweep is a short curved pipe section.
  • For the junction of a branch discharge pipe to a stack (such as the discharge stack or a stub stack),  the connection should either be at 45 degrees or with a sweep pipe section of at least 50 mm radius.
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