Condensation is the change of water vapour into liquid water under suitable conditions. It may be relevant to moisture questions in buildings, but a visible patch does not automatically establish condensation as the cause rather than another source of moisture.
Record where and when moisture becomes visible and any known changes in use. A timeline can help investigate different explanations. Avoid a confident diagnosis based on season, appearance or one isolated reading without a description of the circumstances in which it was obtained.
When roof construction or insulation changes, moisture behaviour belongs in an appropriate assessment of the whole assembly. This site prescribes no simple universal remedy. Ask which information supports the conclusion and how the proposed intervention relates to the situation actually established.
Worth asking
Frequently asked questions
Is a damp patch always condensation?
No. Different moisture sources may need investigation. Appearance alone does not establish the cause.
Does the planner calculate moisture behaviour?
No. It records observations and questions without a building-physics diagnosis.