An emergency roof overflow is an additional drainage provision designed to offer an alternative outlet at a specified water level. It does not replace ordinary rainwater drainage.
What does this mean on your roof?
An opening visible in an edge may have an emergency role, but its purpose must first be established. Position, height and relationship with the roof determine how the provision functions.
Its presence alone does not establish suitability of the whole arrangement. Calculations and checks belong to the responsible professional.
During renewal, establish whether changed roof layers affect an existing provision. Raising an upstand or adding insulation can alter relative heights. Ask what remains and what changes, recording that in the proposal. Report unexpected discharge through an emergency provision so the cause and ordinary drainage route can be investigated rather than assuming the visible flow is routine.
Frequently asked questions
Does an emergency overflow replace the normal outlet?
No. It is an additional provision within a designed drainage arrangement.
Can I choose its height myself?
The decision requires assessment of roof and drainage together, not a generic online dimension.
Consulted 19 September 2026. Check requirements for your own address and selected system.