Moisture Requirements For Growth Of Molds And Wood Decay Fungi

Excess moisture is the single most important factor that will ensure the growth of fungi in buildings. Although food sources for fungi are abundant in most buildings and include materials such as wood and wood-based composite products (Table 8.2), without sufficient moisture, fungi will fail to grow. In any climate the possibility for molds or wood decay fungi to grow and even thrive exists when a problem occurs in a building that allows excess moisture to accumulate. Typical indoor ambient conditions of relative humidity and temperature limit or prohibit the growth of many species of fungi, especially wood decay fungi. However, xerophilic molds prefer dryer conditions and can grow at ambient, although high, relative humidity conditions. Xerotolerant fungi, typically molds, have the ability to tolerate such drier conditions. Thus, in some locations, such as the southeastern United States or other locations where high relative humidity and temperature conditions exist, the

TABLE 8.2. Common Building Materials

Wood-based building materials Wood lumber Surface-treated wood Preservative-treated wood Laminated wood Parquet Cork

Plywood boards Fiberboard Sawdust insulation Cellulose insulation Paper Wallpaper Non-wood-based building materials

Gypsum board [CaSO4-2(H2O), hydrated calcium sulfate]

Ceramics

Paints and glues

Plastics

Wood adhesives Concrete growth of mold will occur under ambient conditions. Also, in cases where temperature gradients exist, condensation can occur when moist, warm air contacts a cooler surface, thus providing an environment conducive to mold growth.

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