Interceptor Traps – Pros, Cons & Upgrades

Why they were installed

Interceptor traps acted as a water seal to stop sewer gases entering homes. They were common in Victorian and Edwardian properties, positioned at the boundary between private and public drains.

• Water trap creates a barrier against odours
• Standard practice in pre-1900s drainage design
• Often found at property boundaries
• Required by historical building regulations

Problems with interceptors today

• Frequent blockages: trap design catches wipes, fat, and debris easily
• Smells: traps can dry out or become poorly maintained
• Difficult access: rodding arms rust shut or fill with debris
• Hard to clean: jetting less effective through trap bends
• Maintenance burden: regular attention needed to prevent issues

Identifying an interceptor

• Chamber near property boundary or street
• Distinctive trap chamber with rodding arm
• Often brick-built with heavy covers
• CCTV survey confirms presence and condition

Modern upgrade options

• Remove and replace: install straight-through chamber for easier maintenance
• Add proper venting: soil stack ventilation replaces trap function
• Improve access: upgrade chambers for better rodding/jetting
• Keep records: document with CCTV before and after

Consult Building Control if making structural changes—they may want to see evidence that adequate ventilation protects against sewer gases.

When to upgrade

• Recurring blockages despite regular maintenance
• Major drainage works or property renovations
• Persistent smells near the chamber
• Insurance claims for repeated flooding
• Property sale requiring drainage improvements