How Many Inspection Chambers Do I Need?
Quick Answer
One at every direction change, junction, and every 45m on straight runs
Typical domestic drainage: 2–4 inspection chambers for a standard extension or new build
When You Need an Inspection Chamber
Building Regulations Approved Document H requires an inspection chamber at:
- Every change of direction (bends greater than 45°)
- Every junction where pipes meet
- Every change of gradient
- Maximum 45m apart on straight runs (22m if no rodding access)
- At the head of each drain run
- Where the drain changes size
Chamber Sizes
- Mini access chamber (150mm): For shallow, single-pipe access points
- Small inspection chamber (315mm): Up to 600mm deep, 110mm pipe
- Standard inspection chamber (450mm): Up to 1.2m deep
- Large manhole (900mm+): Over 1.2m deep, requires step irons
Typical Domestic Example
A single-storey rear extension with separate foul and surface water drainage:
- Chamber at the extension downpipe (surface water)
- Chamber at the kitchen/utility waste connection (foul)
- Chamber where new drain meets existing drain
Total: 3 inspection chambers
Last updated: April 2026