Special Maintenance Considerations - Effective Building Maintenance: Protection of Capital Assets - page 121

Figure 4-3. Indoor Mold Infestation
or balls) of multi-cellular filaments called “hypae.” Some hypae penetrate
the material that is being used for food, making removal very difficult.
Others lie on the surface and develop reproductive structures when
temperature and moisture conditions are appropriate. Fungi are ubiqui-
tous, occurring in soil, in and on plants and animals, and in the ambient
air both indoors and outdoors. Even in buildings without active fungal
growth, total fungi spore concentrations of 3,000-10,000 spores per cubic
meter of air are common.
In any building, any location providing high enough moisture con-
tent and a potential food source will support fungi growth.
Mold will grow on most surfaces if the relative humid ity at the sur-
face is above a critical value and the surface tempera ture is conducive to
growth. The longer the relative humidity remains above the critical value,
the more likely is visible mold growth; and the higher the humidity or
temperature, the shorter is the time needed for germination. The surface
relative humidity is a complex function of material moisture content, ma-
terial properties, and local temperature and humidity conditions. In addi-
tion, mold growth depends on the type of surface.
Fully recognizing the com plexity of the issue, the International En-
ergy Agency Annex 14 (1990) nevertheless established a surface humidity
criterion for design purposes: The monthly average surface relative hu-
midity should remain below 80%. Others have proposed more stringent
criteria, the most stringent requiring that surface relative humidity re-
main below 70% at alltimes . Although there still is no agreement on which