Infrared thermography can be used to locate wet insulation in a ballasted single-ply roof system. The ballast stone does increase the challenge and may require waiting longer after sunset to start an inspection. A higher vantage point can help to pinpoint areas for closer inspection. The standards call for a large inside/outside temperature difference, but this is not always necessary. The main condition is that the ballast stone is spread evenly and has a uniform depth.
The wet area is around the vent and extends diagonal toward the lower left of the thermogram. See next image for a more defined view from above. Ballasted EPDM / EPS insulation / concrete deck. Outside temperature was 73F+/-.
The above image shows the same wet area of the first image, but taken from a the vantage point of a higher roof level. Ballasted EPDM / EPS insulation / concrete deck. Outside temperature was 73F+/-.
EPS insulation wets (absorbs moisture) very slowly and a small wet area like this one only 1-2 feet wide will appear amorphous. Ballasted EPDM / EPS insulation / concrete deck. Outside temperature was 73F+/-.
A distinct board pattern extending from below a raised walkway on the right side. Ballasted EPDM / Polyisocyanurate insulation. Outside temperature was 34F+/-.