Are required when:
- Connections to sewer mains are greater than or equal to 300mm.
- Properties connected to a sewer main directly affected by a pumping or rising main, must include a boundary trap and a minimum of 100mm in-duct vent.
- Within historical boundary trap areas.
- Where it is a trade waste requirement to discharge to sewer via a boundary trap.
- Where a hydraulic assessment review has directed the installation of a boundary trap.