There is a lot of debate on what is needed or required to conduct a building inspection. Is an engineering degree required? Should an inspector be a general contractor? Do you need to be a member of a professional building inspectors association?
One of the statements I make in Level I and II training is that as a thermographer I should be able to take a good image of just about anything. Over the years I’ve taken IR images of household pets, livestock, crickets, and even a praying mantis (of which I’m especially proud). The ability to take a high-quality thermal image of any object should be possible for a seasoned thermographer. However, taking images of livestock doesn’t make me a veterinarian, and my cricket images certainly don’t qualify me as an entomologist. It’s an understanding of the subject matter that qualifies someone to make critical assessments of objects or surfaces imaged. For buildings, what does that look like?
A person must have a basic understanding of building construction methods, basic heat transfer theory with regard to the materials used in construction, and an understanding of what patterns should be present under normal and abnormal conditions. The more a person builds upon this knowledge, with training or certification, the better they will be able to successfully inspect a building. There are a few basic “rules of thumb” that will help you through analyzing the performance of the insulation during a building inspection. And of course, this is only one aspect to a complete building inspection.
One rule for example; once you understand the direction of the heat transfer through the structure based on environmental conditions, an insulated wall cavity should appear the same way that you should feel thermally. In other words, if it is the heating season (inside surface is warmer than the outside surface) and I am outside, I feel cooler than if I were inside. So, an insulated cavity (the space between the framing studs) should appear cooler than the studs.
This is when understanding how heat transfers through different materials and the direction of heat transfer will come into play. By understanding the engineering of the structure to limit the amount of heat flow through the walls, we use materials that are not thermally conductive to fill in the void between the inside and outside surfaces. This will there-by restrict the flow of energy through the structure; in other words, insulate. In the above setup, heat is flowing from the inside of the building to the outside. The framing members (studs that are either metal or wood) are more conductive than the insulation that is in the void between those members, allowing more heat to move to the other surface.
Basic heat transfer theory may point to the answer of the question we started with. Granted there are more factors involved but if we are just looking for insulation problems, this basic rule of thumb will get the job done.