An emergency overflow is a provision with an additional drainage role within a designed roof-drainage system. It is not equivalent to ordinary rainwater drainage. Position, arrangement and capacity should not be inferred from a generic illustration or name alone.
When a proposal includes such a provision, ask its purpose in the actual situation and how it relates to existing outlets and edges. A visible opening in a wall is not complete evidence of function or suitability without further information.
Include the relevant assessment and selected arrangement clearly in the dossier. This website supplies no sizing, level specification or safety statement for your roof. A local planner summary can record the question but does not replace the technical reasoning behind a drainage design.
Worth asking
Frequently asked questions
Is an emergency overflow ordinary drainage?
No. Its additional role should be explained within the selected system.
Does the planner size the opening?
No. It performs no drainage calculation or technical design.