Building inspections are considered the most difficult application for a Thermographer to accomplish. In-experienced Thermographers when first conducting home and building inspections frequently have considerable difficulty conducting these inspections. This inexperience often leads to misinterpreting thermal patterns or outright missing problems.

The first thing we need to understand is building inspections are “Qualitive Inspections.”  By that I mean we are not concerned about temperatures, we are looking for thermal patterns and locations.  Our greatest concern is establishing a thermal contrast that enables us to discern temperature differences indicating areas of heat loss or air leakage pathways. Thermal contrast is so essential we have minimum recommended “Delta T” values for both conduction and air leakage inspections. Those parameters are 18oF, 9oC for the conduction inspection and 9oF, 5oC for the air leakage inspection.

Let us do a little camera operation review.  Span is the portion of the thermal range we are looking at. In other words, the minimum and maximum temperature shown on the camera display.  The data displayed is 8-bit data or 2 times itself 8 times or 256 divisions. This equates to our display providing 256 colors or shades of color.  With a wide span we have less colors or shades per degree or less thermal contrast.  With a narrow span we have more colors or shades per degree or greater thermal contrast. Level is the center point of your span.  When you adjust level, you change the brightness or darkness of the image. You are moving your span up or down the thermal range to achieve the correct brightness.

The most critical camera adjustments, when conducting building inspections, are “Level” and “Span.” In the image above, we can easily see the warm air exfiltrating from the soffits and eaves.  The span setting allows us to readily see the heat loss occurring.  Note the sky; the sky is in saturation, in other words the temperature of the sky is much colder than the temperatures displayed within the span.  If the span was wide enough to include the sky temperature, you would not have sufficient contrast to identify the heat exfiltration.

Many cameras have an “Auto” level and/or span capability.  In that mode the camera will discern the hottest and coldest temperatures detected by the camera array and set the level and span accordingly. This feature will only be useful if you strategically keep the camera FOV away from extreme hot or cold temperatures, lock it or one time auto adjust as needed. When used properly the Auto feature can be quite helpful in identifying temperatures of concern.

What about emissivity and background? These camera settings are not as crucial for building inspections as they are for other applications.  Emissivity should be set at .95 or higher and background temperature set for ambient unless specific temperature measurements are needed to support a finding. Then adjust appropriately. 

In conclusion, proper thermal contrast is essential for successful building inspections.  For more information contact us at the Snell Group or consider attending our Infrared for Building Inspections course.