Penetrating damp occurs when water enters through a defect rather than rising from the ground or forming only as surface condensation. The staining may appear on a wall or ceiling and can become more noticeable during or after rain, although plumbing leaks can produce a similar pattern.
External sources to check
- Blocked, leaking or overflowing gutters and downpipes.
- Damaged roof coverings, chimney details, valleys or flashings.
- Cracked render, deteriorated pointing or failed seals around openings.
- High ground levels, poorly drained areas or water directed against the wall.
Internal sources and secondary damage
Pipework, shower seals, appliance connections and overflows should also be considered. Once the source is repaired, finishes and accessible timber may need time to dry and should be checked for deterioration. Repainting too soon can trap staining or conceal continuing moisture.
Water-repellent coatings are not a substitute for repairing gutters, pointing, flashings or leaks. The correct scope depends on the construction and the defect found.