BRE365 is a guidance document published by the Building Research Establishment (BRE) in the UK, titled "Soakaway Design". It provides methodologies for assessing soil infiltration rates and designing soakaways — structures used to manage surface water runoff by allowing it to drain into the ground. The document is primarily used to support sustainable drainage systems (SuDS), helping developers, engineers, and planners ensure that surface water is managed effectively on-site, thus reducing flood risks and the burden on sewer systems.