Simulation studies on the effect of microbial growth and moisture damaged materials on indoor air quality

In buildings, moisture damage and hidden mold in wall structures can decrease indoor air quality (IAQ) by releasing particles and microbial material. The roles of material moisture state, pressure difference (ΔP), leakage pathways, and insulation together on indoor air quality remain insufficiently resolved. In IAQ simulator, four wall-assembly cases simulated with and without mineral wool insulation, and with and without mold growth under minor (–2 to –5 Pa) and major (–16 to –21 Pa) negative ΔP. Wood material surface relative humidity (RH) and ΔP were monitored continuously. Particles (0.5–7 µm) were measured as inert versus biologic (fluorescent) fractions and compared daily means to material RH changes. Wood material and floor-surface microbial samples were analyzed by cultivation and qPCR. Submicron particles (< 1 µm) were abundant and relatively stable across cases, with no consistent mold or no-mold differences. During drying of the wood material (days 6–7) in the non-insulated mold case, biologic particles increased across size fractions. Pressure pulses produced cumulative increases in small particles and 2–4 log higher floor deposition within three days versus two-week steady runs. Material loads reached up to 10⁸ spores or gene copies g⁻¹, dominated by Penicillium and Aspergillus in mold cases. Particle and microbial transport from moisture-damaged structures are governed by transient phenomena—especially drying phases and pressure pulses—and by leakage configuration and insulation, rather than ΔP or RH alone. Mitigation should prioritize airtightness management, balanced ventilation, and possible structural filtering while accounting for episodic emissions.