02/13/2025
Great thermography does not just rely upon temperature differential between interior and exterior, but also what is referred to as "rate of change of temperature".
Think about it - assuming a warm, sunny day, roof temperature gradually increases, along with underlying substrate layers. At some point, roofing materials will arrive at a relatively similar temperature. Even if an interior/exterior temperate differential still exists at this point, the differential occurs vertically, e.g. colder inside and warmer outside. Likewise, temperature gradient in the roof assembly occurs vertically. Conducting thermography at this time is not effective.
While vertical temperature differential is important, horizontal temperature differential occurs during a "rate of change of temperature".
"Rate of change of temperature" predominantly occurs during dawn and dusk. However, cooling rates are more constant across the roof surface a minimum of one hour after sunset, in part due to solar radiation exposure being eliminated. Conversely, when the sun comes up in the morning, uneven heating of the roof surface and reflectivity of solar radiation is problematic for thermographers.
In Colorado, we have an added benefit of large temperature swings (especially in fall, winter, and spring months).
If an exterior temperature drops from 67 degrees Fahrenheit at 6:00pm to 55 degrees Fahrenheit one hour after sunset, a sharp "rate of change of temperature" occurs. This is the prime time to conduct thermography surveys.
"Rate of change of temperature" results in thermal contrasts between dry and wet materials. Thermal contrasts provide great imagery.
Next step - destructive testing.
