Not the Roof but the Tub
A general contractor called, saying he believed he had a roof leak in a house he had built and asking me to
take a look. I found a patch of blistered paint on the return wall of the home’s main staircase (see slideshow). Moisture readings confirmed that the wallboard in the area was damp. A bathroom upstairs might have been the likely culprit, but the builder had already repaired leaky supply pipes a few months earlier, so now he suspected the roof. However, the initial IR scan showed a pattern of water under the bathtub, so we figured we’d start there.
We turned on the hot water and let it run, then set the camera on time-lapse mode and began scanning. In a couple of minutes, the water began to show up as a bright yellow streak coming down the corner of the wall. (You can also see the hot-water supply pipe running up through the wall to the left.) Then gradually, as the wall was saturated, the hot water filled in beneath the tub, which turned out to be the source of the leak.
As this case illustrates, the moisture stain is often in a different location than the leak, because water will always follow the path of least resistance. The great advantage of the infrared image is that it shows the path, right back to the source.