As the sun works its way across the skies, the shadows it casts can become long and influential. This is especially true on walls where a soffit or overhang can shade the upper part of a wall but not the lower. This is obvious to anyone looking at the exterior (above image), although even there you may see, thermally, the time lag of the moving shadow (see the shades of blue (image right) at the red line).
On the inside, however, it is easy to forget that shading can have such a significant influence, in part because it seems so unlikely (“how can the sun affect a 4+” thick wall?!”) and partly because the effects of solar loading can continue to show up 2-8 hours after the was shining on the exterior surface. Depending on the building materials.
The effects of the sun are real and can be very misleading. The image on the right, taken during the heating season, shows a wall. The pattern may be mistaken as to having the classic thermal pattern of settled cellulose or too short of length fiberglass. Upon closer inspection, however, we notice the pattern changes temperature from top to bottom of the red line, but still indicates the presence of insulation. The cavity is warmer than the framing in both patterns. At this point, you should ask yourself, “is the position of the sun striking or not striking the exterior surface causing a shadow and resulting thermal anomaly?” take a step outside and see what might be happening!
Also keep in mind the source of the shade could be an adjacent structure or vegetation. Always make sure to Think Thermally!® when evaluating findings.