Use this atlas page to organize evidence, not to declare a diagnosis. Frost, roof-deck staining, odor, insulation disturbance and air leakage where indoor moisture meets the roof assembly. The useful starting point is a repeatable pattern tied to location, timing and conditions that changed or stayed normal.
Read the visible pattern
Begin with frost or damp roof sheathing, staining around penetrations, odor that increases in cold weather. Record the first location, direction, edge or cycle where the symptom becomes noticeable. Photograph from the same position, preserve original timestamps and note comparable areas that remain dry, quiet, cool or odor-free.
Trace the connected mechanism
In this room, frost, roof-deck staining, odor, insulation disturbance and air leakage where indoor moisture meets the roof assembly. Compare at least two plausible routes rather than choosing the first familiar explanation. Compare ventilation airflow, insulation airtightness, roof drainage before treating the visible point as the source. A strong hypothesis predicts where the symptom should begin, what trigger should reproduce it and which nearby areas should remain unaffected.
Use safe, non-destructive checks
- Map frost or damp roof sheathing
- Map staining around penetrations
- Compare the ventilation airflow and insulation airtightness pathways
Pair every reading with its instrument, location, time and environmental condition. One reading can support a pattern but cannot certify a hidden material condition or prove that a repair is complete.
Respect the stop boundary
Do not walk unsupported framing, disturb suspect insulation or approach damaged wiring. Active roof leakage, sagging materials or widespread decay needs qualified assessment.
Prepare the next decision
Summarize the trigger, first visible change, rooms or systems involved, checks already completed and what would count as a verified outcome. A useful handoff gives the next person a timeline and competing explanations instead of only a symptom label.
Primary references for this topic family
These references ground the general building-science or safety context. They do not diagnose a specific house, replace local requirements or certify a repair.
