Infrared scanners are quite successful in finding wet roof insulation, especially boards of rapidly absorbing insulations like perlite, wood fiber and fibrous glass. But wet areas develop more slowly and nonuniformly in the cellular plastic insulations, such as urethane, which are commonly used in new roofs. These differences can affect the outcome of an infrared survey of new roofs. To determine the feasibility of detecting incipient wet insulation, several recently constructed roofs were examined thermographically. It was usually more difficult to find moisture in new roofs containing cellular plastic insulations than in new roofs with more-absorbent insulations. This increased difficulty is due to the slower rate of wetting and to the nonuniform manner of wetting of some of the cellular plastics. Perlite, wood fiber and fibrous glass insulations tend to become uniformly wet throughout an entire board, whereas moisture initially concentrates at the perimeters of boards of some cellular plastic insulations. However, eight to ten months after construction, enough moisture can accumulate in most cellular plastic insulations to be visible to aninfrared scanner. Since this moisture is concentrated in a small portion of each insulation board, much of it would probably be overlooked by a nuclear or capacitance grid survey.