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We recently did some thermal roof inspection work for a client who was new to the realm of thermal imaging. They understood the potential benefits of utilizing thermal imaging for roofing applications, but they weren’t familiar with the thermogram interpretation process.

So, we had the opportunity to provide the client with a comprehensive tutorial on thermogram interpretation. We always include a basic interpretation guide in our thermal inspection reports, but if a client wants a more in-depth explanation, we’re happy to provide it.

In this guide, we will focus on thermal image interpretation in the context of flat roofing.

What is a Thermogram?

Before we talk about interpreting a thermogram, we’ll talk about what a thermogram is. Simply put, a thermogram is a visual depiction of the infrared radiation information of an object or scene.

Objects emit a certain amount of infrared radiation (which can basically be thought of as heat energy), and there are sensors (cameras) designed to capture this information and display it as an image that we can see and interpret. Objects that emit more infrared radiation will appear differently than objects that emit less infrared radiation.

What is a Thermogram Used For?

Now that we know what a thermogram is, we will discuss its practical application. In simple terms, a thermogram is used to ascertain the condition of some type of critical asset or infrastructure by comparing the relative temperature of an object of interest and its surroundings. When it comes to interpreting these differences, thermographers refer to notable temperature differences as thermal anomalies.

In our case here, the critical asset is a flat/low-slope roof, and the temperature anomalies of interest indicate the presence of moisture that can cause damage to the roof and its underlying foundation. If a flat roof leaks, the roof foundation and the insulation can be damaged, and mold can develop. For this reason, moisture ingress is one of the biggest concerns when it comes to flat roof integrity.

Thermal imaging allows roofing companies, insurance agents, and property owners/managers to gain a level of insight on their asset in a way that conventional visual inspection methods simply can’t provide. The bottom line is that, when it comes to structural damage, leaks, and other asset issues, thermal anomalies provide an invaluable amount of actionable information.

Read about how we used a thermal drone to assess roof damage for a local charitable organization.

Interpreting a Thermal Image

Now that we have established what a thermogram is and what they are used for, we’ll discuss the basics of interpreting them in the context of flat roof water detection. This won’t be an all-encompassing tutorial but rather a concise guide to aid in thermogram interpretation.

Provided the thermogram is captured after sunset (which is the ideal time for thermal flat roof inspections), underlying moisture issues appear as “hot” spots compared to the cooler parts of the surrounding roof.

Below is an example of a thermogram taken from a recent inspection project in the IronRed color palette. With this color palette, warmer areas are depicted in brighter, warmer colors. In this example, the warmest portions appear yellow, and the coolest portions appear dark purple.

The warmest part of this scene is the concrete at the bottom of the image; concrete retains heat much longer than other materials, so this is why it appears so much warmer.

With this color palette, the areas of interest tend to be closer to orange; these areas indicate the presence of underlying moisture.

At this point, you might be asking — why would water appear warmer than the surrounding roof? Well, similarly to concrete, water tends to retain heat for longer than most other materials. So, after sunset, the surrounding roof cools off much more quickly than the areas that are saturated with water, so these areas will appear much warmer.

So, in the image below, the bottom edge of the roof has a significant amount of moisture.

For more information on aerial thermal imaging, check out our thermal roof inspection service page.

There are all kinds of color palettes that can be used with thermal imaging. But for roofing applications, another helpful option is a palette called Black Hot, as seen below.

With this color palette, areas with underlying moisture will appear closer to black. In this image, you might think the lighter-colored areas are moisture, but these areas are much cooler than the surrounding roof, which means there actually isn’t moisture there. It’s likely that these are areas where sediment and debris have accumulated on the surface of the roof.

In this scene, the areas of interest are darker.

And there you have it — the basics of thermogram interpretation in the context of flat/commercial roofing!