Mold growing in attic — Haarlem, Noord-Holland

Mold in the attic usually signals a ventilation or moisture problem rather than a plumbing leak. The most common cause is inadequate soffit-to-ridge airflow: when warm, humid air from the living space rises and has no way out, it condenses on the cold underside of the roof sheathing and feeds mold colonies. Bathroom exhaust fans or dryer vents that terminate inside the attic instead of outdoors are another major culprit. Roof leaks — even small ones around flashing, valleys, or pipe boots — can also introduce enough moisture to start growth. Health-wise, attic mold can circulate spores into the HVAC system and living areas, aggravating allergies and respiratory conditions. A roofer or insulation specialist inspects ventilation pathways (soffit vents, ridge vent, gable vents), checks for exhaust fans venting into the attic, and evaluates roof integrity. If mold coverage is extensive (typically over 10 sq ft), a licensed mold remediation professional should handle removal before ventilation corrections are made.