A dark patch on a ceiling can signal a leak but a simple photo with your smartphone's camera is not sufficient to confirm water. Infrared (thermal imaging) surfaces by their surface temperature whereas moisture measurement tests the electrical properties of a material that change with moisture. This important distinction is useful for home owners, property managers and property inspectors alike as it helps not to confuse useful information with the end of the investigation and selecting the appropriate verification step.
The ceiling stain that starts the investigation
A typical scenario: A home owner notices a pale brown spot on his living room ceiling from below a bathroom on the upper floor. Days pass and the brown patch does not change in color or size. It is dry to the touch. The thermal image acquired for the investigation shows a slight cooler area in the stain's vicinity.
The pattern of heat loss or gain at the ceiling stain is an area of interest to the inspector but does not prove the ceiling has water in it. The cooler area(s) may be the result of evaporation, a decrease in insulation, air movement through the ceiling, a framing member or other object in the ceiling space, or the different material(s) used in the ceiling.
While the temperature difference described above can indicate the presence of moisture in building components, it is important to note that surface temperature also can be affected by other factors, and therefore must be verified with appropriate tests.
What a thermal image actually shows
Thermal imaging uses an infrared camera to detect the difference in infrared energy emitted from surfaces. In building investigations the differences in apparent surface temperature, shown as a picture on the screen, are of greatest interest. A section of drywall may appear cooler or even warmer than adjacent areas under seemingly similar conditions.
The patterns that indicate heat loss, are caused by air leaks, lack of insulation, thermal bridges, problems with heating system distribution and some moisture problems in buildings. Camera is ideal for scanning large areas without having to open up walls and ceilings.
The surface temperature of objects is determined by a large number of factors and those factors can make a large difference in the reading of a surface. Typically, surface temperature of objects in a given space is affected by room conditions, such as temperature, sunlight entering the space through windows and other openings, air movement, such as from heating, air-conditioning and ventilation systems, as well as from outside doors and windows, the surface finish of objects, the viewing angle of the thermometer, and the ability of an object's surface to emit thermal infrared energy.
Thermal images of surface temperatures can look like photographs of wet areas but really are just maps of temperature. Temperature of surfaces can change for many reasons and moisture is only one of them.
Why moisture can create a temperature pattern
When moisture exists in a building material, the way it loses and gains heat can change. A damp area generally loses heat by evaporation from the surface of the material. This can result in an irregular, cool region that contrasts with the surrounding material such as drywall, insulation, masonry or flooring. In some cases the unusual temperature reading may extend from the obvious moisture stain. In other cases the older stain may have long since dried out but still show up on the thermal image.
Moisture can penetrate further into a building than is apparent from a stain. The water may travel along a joist, or spread beneath a floor finish. In some cases the stain may remain long after the material has dried. The corresponding thermal change may have disappeared by then.
As was the case for locating moisture on walls, when using thermal imaging to look for hidden moisture, images of suspicious areas and their relation to surrounding building features can be valuable, but the material being imaged must be determined to be moisture affected by its temperature alone.
What a moisture meter adds at the wall
The moisture meter in turn provides completely different evidence for the presence of moisture, i.e. the measurement of an electrical property of the building material which changes with the moisture content, and thus indicates the moisture content (in %).Pin meters and non-invasive meters (doortex meters, LD meters, spike meters) are available for the different building materials. Each type has its specific application area and possible sources of error.
In addition, there are further restrictions which must be considered when using a moisture meter for the measurement of water content in building materials. These restrict the meaningful measurement of the exact amount of water in a building material. Above all, the reading obtained from a moisture meter must be compared with other readings from undamaged material of the same type.
On the ceiling with the yellowish discoloration, compare the suspected areas with seemingly unchanged regions of the same type of construction material. Higher values in the cool area would support a moisture-related cause of damage. Identical values in suspect and reference locations suggest that a greater area may be affected than indicated by the visible staining and that the damage may extend beyond the affected material.
How the two tools work as a pair
Inspect with camera and then go to that location and use the meter to check for moisture at the surface of the material found in the thermal image.
Using Thermal Imagery to Find a Ceiling Leak and Moisture Measurement to Confirm the Suspected Area for Moisture. This diagram explains how to use thermal imagery to confirm that a suspected area for moisture is a wet area and then how to use a moisture meter to confirm that the suspected area for moisture has an elevated moisture content.
Documentation of surface and thermal images as well as moisture measurements should include details of room conditions as well as material(s) tested at given locations. Subsequent inspections of suspected leaks can assist in differentiating between a changing moisture-related problem and a building feature that remains unchanged over time.
When a cool patch is an energy problem instead
Investigations of energy losses can have similar results. Areas of a building, such as where a wall meets a ceiling, around windows, near where duct work, electrical components, etc. penetrate the ceiling, all can appear cool and might suggest moisture problems. Conversely, an area appears warm and there is suspicion that there may be hidden moisture. The thermal image can reveal the extent of heat transfer but that does not tell us if the moisture is unwanted.
During an energy-efficiency survey, the decision-maker needs to establish whether the temperature-measurement results, as detected by the thermal-imaging camera, are indicative of hidden moisture, i.e. a possible water leak; or simply indicative of energy loss.
In this way the diagnostics are kept in check and should not lead to over expensive repairs of energy-deterioration or of concealed damage.
A clearer decision after the scan
The results from the inspection of the stained ceiling are shown on the right. Infrared inspection showed up areas of unusual surface behavior on the ceiling. Moisture measurement was taken at several of these locations to determine if the material(s) tested were indicating moisture related problems presently. Where plumbing or roof problems exist further investigation is required to verify the source of problem, and later measurements will show if the problem is increasing.
None of the new testing methods replace close observation, but when used in proper combination, each can answer specific questions. Infrared testing can identify surface temperature patterns. Moisture testing can determine if a material has a moisture-related problem. Remember that the thermal imager is looking at surface temperature and the moisture meter is taking readings from the material(s) suspected of having a moisture related problem. The questions that must be answered are: 1) Where is unusual surface behavior occurring? 2) Does this material have a moisture-related problem?
