Interior humidity stayed high overnight
The room generated and retained moisture while the door remained closed.
↓House Autopsy · windows-and-doors
The window marks that followed cold edges
Dark speckling returned along the coldest frame edges where condensation and low air movement overlapped.
Trigger conditioncold nights and high indoor humidity
Four layers, one connected story.
Frame edges cooled below nearby wall temperature
The geometry created a repeatable cold perimeter.
↓Condensation retained dust and supported spotting
Color alone could not distinguish dirt, soot and growth.
↓Temperature and humidity changes altered recurrence
The pattern weakened when airflow and humidity control improved.
Canonical connection
The symptom and cause are separate objects.
The autopsy preserves how evidence connected them without collapsing uncertainty into one magic answer.
Dark speckling returned along the coldest frame edges where condensation and low air movement overlapped.
The visible symptom was the final chapter
The investigation followed the source, transport path, affected material and verification step separately.
What changed the direction
Timing and location evidence ruled out attractive but weaker explanations before repair work began.
The durable lesson
Repair the controlling source and then verify the outcome under the conditions that previously triggered the symptom.
Source→Path→Damage→Verify
