Scope: This article supports product selection and technical discussion. It does not replace the project designer, local building code, approved construction details or product-specific declarations.
Record when and where water appears
Water below a metal roof is not automatically a roof leak. Record weather, indoor humidity, operating schedule and the position of wet insulation. Condensation often appears during cold nights, start-up heating or periods of high internal moisture generation.
Trace moisture through every layer
Inspect the interior air and vapor-control layer, insulation joints, thermal bridges, fastener penetrations and the exterior breathable layer. Wet insulation loses thermal performance and can move the condensation plane, so moisture content should be investigated rather than covered.
Separate repair from prevention
Repair damaged seams and penetrations, but also correct the moisture source and drying path. Ventilation, dehumidification, insulation continuity and airtightness may be more important than adding another exterior sheet. Any remedial detail must retain safe drainage to the exterior.
Project checks
- Log indoor relative humidity and outdoor temperature.
- Inspect warm-side continuity before blaming the outer membrane.
- Confirm drainage and ventilation paths remain open.