What should I do first when a new house symptom appears? Use a controlled observation window when the condition is stable, non-urgent and likely to become clearer through comparable records.
What to compare
Record the first location, timing, trigger, recent change and an unaffected comparison area. Keep weather, occupancy and system state with every photograph or reading.
What the evidence cannot prove alone
A single reading, image, smell or temporary improvement cannot certify a concealed source. Keep at least two plausible pathways visible until repeatable evidence separates them.
Safe next step
Use the site as an information and evidence tool. Stop ordinary self-help at electrical, combustion, contamination, structural, access or acute-health boundaries. Continue with Document and monitor for a bounded action, stop rule and professional handoff route.
