Curtain walls may contain a cavity between the interior finish wall and the exterior cladding. Condensation can occur in this space as interior moisture enters either through direct air leakage paths or diffusion through construction materials, and can significantly affect the facade life expectancy. Buildings exhibiting facade degradation due to cavity moisture generally require detailed evaluation in order to determine the source, and to develop an appropriate repair plan. One tool available to the investigator is field testing. This paper will address typical wall behaviors and the practical aspects of field instrumentation to acquire data for determination of the presence or absence of cavity condensation, and a time history of its occurrence.