Trace dampness fast with a structured checklist. Compare room conditions to spot hidden water pathways. Get clear next steps for safer, drier construction projects.
Provide measured site conditions. Use multiple readings if possible.
Sample site readings showing how outputs change with conditions.
| Indoor Temp | Indoor RH | ACH | Surface Temp | Leak Flags | Likely Top Source |
|---|---|---|---|---|---|
| 24°C | 68% | 0.25 | 16°C | None | High Indoor Humidity |
| 21°C | 62% | 0.40 | 13°C | Thermal bridge | Condensation / Thermal Bridge |
| 23°C | 55% | 0.50 | — | Plumbing leak | Plumbing Leak |
| 25°C | 60% | 0.35 | — | Water event (3 days) | Recent Water Event |
This calculator blends building-science checks with weighted scoring.
dew point − surface temperature; positive suggests wetting.Mold needs moisture, time, and food. The fastest investigation starts by separating “bulk water” from “air moisture.” Bulk water comes from leaks, rain entry, or floods, often producing sharp boundaries and elevated meter readings. Air moisture comes from sustained high relative humidity, weak exhaust, and low ventilation, usually affecting multiple rooms. This calculator ranks likely sources so teams can focus inspections where the evidence should be strongest. Use room-by-room notes to link symptoms, materials, and timelines, then retest after corrections to confirm stability seasonally and quickly.
Relative humidity alone can mislead because warm air holds more moisture than cool air. Dew point converts temperature and RH into a single moisture indicator. If dew point stays high, materials dry slowly and hidden cavities can remain damp. Use steady readings over 24–48 hours, then compare to the building’s operating setpoints and occupancy patterns.
Condensation occurs when a surface temperature drops below the indoor dew point. Corners, slab edges, steel framing, and poorly insulated windows create thermal bridges that cool surfaces. The calculator’s “condensation potential” value (dew point minus surface temperature) highlights this risk. A positive value suggests likely wetting during normal operation, especially when window condensation is frequent.
Plumbing leaks often show localized peaks at cabinets, valve walls, or wet ceilings below bathrooms. Roof and rain intrusion commonly track with storms and appear along rafters, penetrations, and exterior walls. Foundation moisture is tied to grading, downspouts, drainage, and capillary rise at slab edges. When leak flags are marked, the ranking shifts toward these pathways.
Treat the ranking as a decision aid, not a substitute for inspection. Confirm with moisture mapping, infrared scanning where appropriate, and targeted openings. After repairs, dry assemblies quickly, remove unsalvageable porous finishes, and verify moisture content before closing cavities. Document readings, dates, and locations to support quality control and to reduce recurrence on future projects.
1) What do the likelihood percentages mean?
They are a relative ranking across sources using your inputs. A higher percentage means the pattern fits better, not that the cause is confirmed.
2) Why is dew point important for mold control?
Dew point represents actual moisture in air. When surfaces fall below it, water can condense and keep materials damp even without visible leaks.
3) What surface temperature should I enter?
Use the coldest suspect surface: window glass, exterior corner drywall, slab edge, or metal framing line. A simple infrared thermometer works well.
4) I do not know ACH. What should I do?
Start with a best estimate. Older tight rooms may be 0.1–0.3, typical homes 0.3–0.6, and mechanically ventilated spaces higher. Update inputs when you measure.
5) How should I use moisture meter readings here?
Treat the meter value as a comparison index. Map multiple points and look for sharp peaks near a boundary. Rising readings after drying often indicate ongoing intrusion.
6) When should I bring in a specialist?
If you see widespread growth, repeated wetting, sewage impacts, hidden cavities, or health-sensitive occupants, hire qualified remediation and building diagnostics support.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.