Soil or Waste Stacks

A soil or waste stack (normally just called a stack) is a drainage pipe that passes through at least one story(floor to ceiling) as a drain pipe, this also includes any horizontal offsets. Every soil or waste stack will terminate in a stack vent that leads to outside air or a vent header. Stacks will typically receive waste from multiple fixtures connected to it, which may be located on a single floor or multiple stories.

Rules for soil or waste stacks

A soil or waste stack is a key component in most plumbing systems and as such they have specific rules applied to them so the system will function properly. Such as: (may be different for your area)

• Every stack must have a cleanout located near the base to facilitate cleaning;
• May not reduce in size in the direction of flow;
• The farthest stack serving a water closet must continue to fresh air at not less than 3″ to assist in venting the public/private system;
• Horizontal offsets in a stack longer than 1.5m are to be sized as a branch or a building drain, which ever is larger.
• Stacks are sized by the number of drainage fixture units it receives as well as from each story, but may have overriding factors that increase it’s size.