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ISO 9223 Time of Wetness (TOW)
SPATIAL
Some elevations stay damp long after the rest of a building has dried — north faces, shaded valleys, frost pockets, and anywhere fog or river mist lingers. Time of Wetness is the measured number of hours a surface stays wet enough for growth to take hold, defined by an international standard (ISO 9223). It explains why one wall greens while another stays clean, and sets how often a property genuinely needs cleaning to stay ahead of it.
Time of Wetness (TOW) is the standardised environmental parameter — defined in ISO 9223, the international corrosivity-of-atmospheres standard — for the cumulative time a surface is wet enough to sustain electrochemical and biological activity (conventionally, relative humidity above 80% at temperatures above 0°C). In ATH it is the master spatial driver of colonisation: organisms establish only where the wetness window is long enough, so TOW governs which aspects, microclimates and substrates carry risk. It feeds the COSMOS Time-to-Failure model alongside Arrhenius temperature scaling and deposition velocity, converting a property's microclimate (river-valley fog, frost pockets, shaded north elevations) into a quantitative colonisation and maintenance-frequency signal.
hyphal activation, spatial humidity
Time of Wetness (TOW) is the standardised environmental parameter — defined in ISO 9223, the international corrosivity-of-atmospheres standard — for the cumulative time a surface is wet enough to sustain electrochemical and biological activity (conventionally, relative humidity above 80% at temperatures above 0°C). In ATH it is the master spatial driver of colonisation: organisms establish only where the wetness window is long enough, so TOW governs which aspects, microclimates and substrates carry risk. It feeds the COSMOS Time-to-Failure model alongside Arrhenius temperature scaling and deposition velocity, converting a property's microclimate (river-valley fog, frost pockets, shaded north elevations) into a quantitative colonisation and maintenance-frequency signal.
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