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What Can Cause a Damp Patch on an Internal Wall?
The position, timing and moisture source matter. Treating the visible stain before diagnosing the cause often wastes money.
BuilderFind editorial · 6 min read
Look for a pattern
A patch after rain suggests a different route from moisture appearing during showering or when heating is off. Note weather, room use and whether the patch changes.
Check nearby services
Supply pipes, wastes, heating pipes and appliance connections can leak slowly. A plumber may pressure-test or expose a small area when the source is concealed.
Consider condensation
Cold surfaces, limited ventilation and high internal humidity can create local mould or dampness. Insulation and ventilation need to be considered together.