Explain the property of materials employed for roof, moisture surveys?

• A. Thermal Conductivity
• B. Thermal Diffusivity
• C. Emissivity
• D. Thermal Capacity Difference

Answer: (D)

Moisture surveys with infrared thermography rely on how moisture changes the heat stored in roof materials. Water increases the material’s thermal capacity (thermal mass), so wet areas can store more heat and resist temperature changes more than dry areas. During solar heating or subsequent cooling, these differences in heat storage cause moisture-affected patches to lag behind their dry surroundings, producing observable temperature contrasts on IR images. That contrast is what reveals moisture presence. While emissivity and other heat-transfer properties influence the exact signal, the key factor that makes moisture detectable in roof surveys is the difference in thermal capacity between wet and dry regions.