Air leakage into the attic

Air leakage, insulation, ventilation, frost, ducts and roof-deck moisture.

Frost on cold roof surfaces often reveals warm humid indoor air reaching the attic and freezing before it can dry.

Convective air transport can spread moisture across the attic before it freezes on the coldest roof surfaces.

Air leakage carries indoor moisture into a cold attic where it freezes on roof sheathing and later melts.

A disconnected or intentionally terminated duct delivers concentrated warm moisture to cold attic materials.

Exhaust equipment or stack effect pulls air through floor and service penetrations from a damp crawl space.

Convective air transport can spread moisture across the attic before it freezes on the coldest roof surfaces.

A rain-linked earthy odor often means moisture is reaching a hidden material or changing airflow through a damp area.