What happened

An extension's foul drainage ran beneath the new ground-floor slab. The drainage was tested before the slab was poured, but the rodding access at one bend was omitted from the design.

How it was discovered

A minor blockage two years post-completion. The cleanout was inside the slab.

The consequences

Floor opened, access chamber retrofitted, floor reinstated. The fix was workable but expensive.

What homeowners can learn

Drainage layouts must include access for future maintenance, not just current compliance. Push for this at design stage.