Infrared False Positives In Home Inspection

Marc Mazza Blog

The testing in which I’ve performed here is to demonstrate false positives and the differences between materials and conditions which are common in the home inspection industry and thus create possible mistakes home inspectors can make while using infrared as well as other test equipment and identifying issues which are thought to be primarily moisture related. Our tests were performed within a contained environment with the amp temperature of the confines at 72-73.8F and RH 15.3% at the time of the tests. The infrared camera used for these tests is the FlirT640 and the moisture meter is a Flir MR77. Our testing was of the gypsum surface only.

The water temperature chosen for this test was taken from an average of water temperatures throughout the available building in a Southern California Climate within the month of November. The exterior ambient temperature at the time of the tests was 76 degreesF. Note that tests will vary from state to state climate to climate and season to season. This test on this day was merely a snapshot in time.

The tests are broken down into four tests which represent four possible and real-life scenarios in which a home inspector may find themselves in while conducting infrared surveys within the confines of a buildings envelope.

infrared thermography false positive test


false positives in thermographyTEST ONE

This test is to simulate the affects which cooled water within a trap radiates its energy onto the ceiling below the trap thus creating an illusion that the ceiling is intact wet.  The typical plumbing trap was installed directly above the test area ceiling, but not making physical contact. A 1/8′” gap between the trap and the ceiling gypsum board. The trap was filled with water which was cooled to a temperature of 55F degrees prior to adding into the trap. Note we do not have running water for this test, so water cooled to 55degrees F will have to suffice in order to simulate running water within a bathtub trap. This test of the ceiling temperature was conducted over a 9 minute span and 14 seconds intervals between images taken. Also note we did not perform nor did we calibrate the emissivity within the camera as most home inspector have the camera set to 1 when scanning drywall.

Infrared thermography false positive test

false positives in thermography


This test is to simulate the affects conduction has when actual water has when applied to gypsum board material in order to thus simulate an actual water leak from in this example, a bathtub trap. In this test we used the same cooled water (55F) and applied it directly into a cup which was placed onto the ceiling of the gypsum board with the use of silicone. The test of the ceiling temperature was conducted over a 9 minute span and with 14 seconds intervals between the images taken.

Infrared thermography false positive test 3

false positives in thermography


This test is to simulate the effects which metal structural hardware has on gypsum board material as the cooler metal via which makes direct contact to the gypsum board, thus conducts cooler energy onto the surface of that material illustrated here. Some may argue that hardware should never make contact with gypsum board within a ceiling or wall cavity, however, this is not always the case and when conducting infrared analysis during a home inspection the operator should never assume anything. In this test the metal was cooled to the same 55F as was all the other materials used. This may not seem typical to some, however, I will argue that in order to see a noticeable difference in temperature the subject material must be of a greater differential in temperature than is our surface test material in order to NOT have a temperature equilibrium. One may also make the case that ceiling cavities are in some cases significantly cooler than interior ambient temperatures as some of these cavities can be vented to the exterior as in the case of floor joist construction, ceiling construction exposed to an attic, floor joist cavities exposed to the exterior directly via soffit or exterior sidewall ventilation or air duct or exhaust ventilation leakage.

infrared thermography false positive test


Test four is a test of a typical gypsum clad wall system, wood framed with metal corner beading. Our test is primarily focused on the affects which the metal corner bead produces when tested for potential moisture intrusion either exterior or interior, and the affects which a typical wall system produces when subject to air infiltration or air movement of some type, which is typical in residential building construction. This exposure to air movement can come in the form of natural drafting, intentional ventilation, leaking ducts or exhaust vents to name a few. This test will demonstrate the results of a test performed first with an infrared camera and then followed up by a moisture metering device.

Other Observations

false positives in moisture reading


MAZZA Inspection group infrared