Approved Document H5 (separate systems)

Approved Document H5 provides guidance on the separation of foul water and surface water drainage on new buildings and developments. The document supports the wider planning preference across England and Wales for separate systems rather than combined drains, which can overload during heavy rainfall and contribute to combined sewer overflows. The guidance applies to new builds, large extensions and certain refurbishment works under Building Regulations 2010, and is enforced by Local Authority Building Control. In Greater London, the London Plan and Thames Water consenting practices further reinforce the preference for separation where practical. Practical implications for homeowners include the need to identify the existing drainage arrangement before commissioning new work, and to route new run-off to a separate surface water drain, soakaway or SuDS feature where possible. The formal reference is Approved Document H, Volume 5: Separate systems of drainage.