The cavity dew point temperature and the cavity surface temperature were plotted on a graph, as shown in Figure 2. The solid area in the graph illustrates that condensation is occurring and that moisture is supplied constantly to the cavity throughout the 14-day period represented by the graph. Examination of the pressure difference across the wall confirmed that air exfiltration is occurring. The area of most severe damage should be monitored. Temperature sensors record the interior, exterior, and cavity temperatures.
Relative humidity is measured at the same locations.
It is also recommended that the cavity and exterior be instrumented with pressure taps to measure pressure difference during rain events to discriminate between rain penetration by gravity and rain penetration by wind-driven rain. All sensors should be connected to a data logger set with a continuous loop and a monitoring interval of 10 minutes. Data can be retrieved after a rain or melt-water event. Two or three events should be recorded. Following a rain storm or melt-water event, if the relative humidity in the cavity rises and remains high for days or even weeks, it is likely that rain or melt water has penetrated the wall construction and that it is not draining or drying out adequately.