Moisture and Humidity Risk Assessment Calculator
Evaluate moisture and humidity risk for buildings, materials, and environments using temperature, relative humidity, dew point analysis, and mold growth potential indices.
Formulas Used
1. Dew Point (Magnus / Lawrence 2005):
γ(T, RH) = ln(RH/100) + (17.625 × T) / (243.04 + T)
Td = 243.04 × γ / (17.625 − γ) [°C]
2. Saturation Vapour Pressure (Buck equation):
es(T) = 0.61121 × exp[(18.678 − T/234.5) × T / (257.14 + T)] [kPa]
3. Actual Vapour Pressure:
e = (RH/100) × es(Tair)
4. Surface Relative Humidity:
RHs = (e / es(Tsurface)) × 100 [%]
5. Humidity Index (HI):
HI = 0.5 × RH + 0.3 × RHs + 0.2 × min(duration/720, 1) × 100
6. Mold Growth Risk Index (MGRI, 0–10):
MGRI = RHs-factor × duration-factor × material-factor × 10
(Based on ASHRAE 160 / ISO 13788 mold growth thresholds; RHs ≥ 80% critical)
7. Corrosion Risk Index (CRI, 0–10):
CRI = (RHs/100)² × min(duration/720, 1) × 10 × material-factor
(Based on ISO 9223 atmospheric corrosion classification)
8. Overall Risk Score (ORS, 0–100):
ORS = 0.40 × HI + 0.40 × (MGRI × 10) + 0.20 × (CRI × 10)
Assumptions & References
- Dew point calculated using the Magnus formula with constants from Lawrence (2005), BAMS.
- Saturation vapour pressure uses the Buck (1981) equation, accurate to ±0.02% over −40°C to +60°C.
- Mold growth thresholds based on ASHRAE Standard 160-2016 (Design Criteria for Moisture Control in Buildings) and ISO 13788:2012.
- Corrosion risk classification follows ISO 9223:2012 (Corrosion of metals — Corrosivity of atmospheres).
- Material susceptibility factors are indicative; actual values depend on specific product composition and surface finish.
- Duration normalised to 720 hours (30 days) as a reference chronic exposure period.
- Model assumes steady-state conditions; transient effects (e.g., thermal bridging, vapour diffusion) are not modelled.
- Risk thresholds: Low <20, Moderate 20–40, High 40–60, Very High 60–80, Extreme ≥80.