Odour before appearance
A musty smell that returns after ventilation often indicates damp material somewhere out of sight, such as insulation in a wall cavity or underlay beneath flooring.
Movement in materials
Cupped hardwood, swollen baseboards, lifting laminate edges and doors that suddenly stick can all point to moisture in the assembly rather than a surface spill.
Finishes that change
Bubbling paint, softened drywall, staining that reappears after painting and efflorescence on masonry are common indicators worth investigating with meters.
This guide is general information. Conditions vary between properties, so decisions about your building should follow an assessment of the affected areas.