When does a roof leak become an emergency?

Running water means the route is now open and the volume is only limited by the rainfall. A bulging ceiling means water is pooling above plasterboard, which can fail without warning. Water at fittings or cables is an electrical hazard regardless of quantity. An open roof after storm damage will keep taking water in until it is covered.

Each of these is about protecting people and preventing further damage, which is a different job from diagnosing the fault.

Move what can be moved and cover what cannot. Put containers under drips and, if a ceiling is holding water, keep out of the room. Where water is near electrics, isolate the circuit at the consumer unit if it is safe to do so, and do not touch fittings.

Do not go onto a wet roof. Nearly every serious injury we hear about in these situations happens during an attempt to fix something in bad weather.

Emergency work is about making the building watertight and safe: securing loose components, covering an opening, easing pressure on a ceiling. It is deliberately temporary, and it is normally followed by inspection in dry conditions before a permanent repair is specified.

Keeping dated photographs of the damage as found, before any covering goes on, is worth doing for both the diagnosis and any claim you may make.

Look at how the water is behaving rather than only how much there is. Water dripping steadily at a constant rate from one point is generally more manageable than water appearing at several points at once, which suggests either a larger area of failure or water spreading sideways across a membrane or ceiling void before finding its way down.

A sudden change in sound, such as dripping becoming a trickle or a new area starting to show damp, is worth acting on immediately rather than waiting to see if it settles down on its own.

Once the property is safe and water is no longer actively entering, resist the urge to start drying everything out before it has been assessed. A damp patch or a section of stained ceiling can hold information about how long ingress has been happening and how far it has spread, which is useful to whoever diagnoses the cause afterwards.

Ventilating the room and running a dehumidifier is reasonable once photographs have been taken, but avoid stripping out plaster or insulation before the roof itself has been looked at and the cause confirmed.