Write down when it leaks
If the mark only appears during wind from one direction, say so. If it takes several hours of steady rain before anything shows, say that too. Those details matter. They can separate an overlap problem from a blocked outlet or a roof detail that only becomes saturated after prolonged wetting.
Do not wipe away all the evidence before taking a photograph. A pencil mark around the edge of a stain can help you see later whether it is still growing.
Use the loft if it is safe
From proper boarding, shine a torch above and uphill from the damp patch. Wet rafters, rusty nail points, dark felt or compressed wet insulation can help trace the route. Water often follows timber for a while before dropping.
If the loft is damp over a wide area on a cold morning, condensation becomes a stronger possibility. That needs a different remedy from a broken slate.
Outside, look wider than the stain
Check the covering above the room, then move uphill towards the ridge. Chimneys, valleys, roof windows and wall junctions can all send water sideways. A slipped slate two metres away can still be relevant.
From the ground you are looking for change: a piece out of line, a lifted corner, a crack, loose mortar or debris in a gutter. Close inspection at height is a roofer's job.
What a sensible repair should do
The repair should deal with the route water is taking. A smear of sealant from inside the loft may interrupt the drip but it can also divert the water to a new place. Roofing works by overlapping materials so rain stays outside.
Once the fault is repaired, give soaked insulation, plaster and timber time to dry before deciding that the repair has failed.
Want local roofers to look at the job?
Describe what you have noticed and, if you can, include when it happens and which part of the roof seems involved.
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