Moisture is an efficient conductor of heat energy. Wet insulation is in worse than no insulation. Underlying moisture in flat roofs can often be detected and visualised with high resolution infrared thermal imaging equipment operating in the appropriate wavelength.
Flat roofs with parapet walls and / or any penetration of the roof membrane often leak with the manifestation of damp walls and ceilings in the lower floors. Parapet walls are a weakness with respect to water ingress, especially on tall buildings. High winds around internal and external wall angles can create eddies which double back on themselves and in turn create miniature whirlwinds. When carrying rain or dense water vapour, the high increase in velocity can penetrate the smallest of gaps.
There can be numerous ways that water can ingress into a parapet wall and track down the inner skin.
Parapet internal corners. These areas are especially prone to leakage because of the wind effects and the more complex and more fragile DPC detail both in the parapet wall and the skirting.
The thermal image above shows saturated brickwork above the Damp Proof Course material and a lower characteristic funneling shape where the DPC has been bypassed. The moisture in this case can be seen not to have entered under the asphalt roof covering but had travelled to the walls and ceiling of the floor below.
Although in this case the moisture was not visible to the naked eye, care must be taken with infrared equipment to ensure the images are interpreted properly. External moisture is constantly evaporating and therefore appears cold. Sub-surface moisture can have the opposite thermal appearance since it may be heated from the building and is slow to change with respect to ambient changes. A thermal imager is therefore used as a tool to very quickly detect and provide a visualization of moisture patterns, extent and travel direction. Density layers density slicing) can often be visualized as temperatures and this may be interpreted to determine the core of the moisture. The data then must be confirmed by more conventional conductivity and other testing methods.
Sub-surface moisture is usually easy to detect and display on a thermal imager. Moisture is an efficient conductor of heat energy and damp areas will display a differential surface temperatures) to the surrounding dry areas.
Blisters in the asphalt on a flat roof. Asphalt being black absorbs solar gain and undergoes extreme changes in temperature and some movement throughout the year. Blistering however is normally caused by underlying trapped moisture which vaporizes under heat. The vaporization creates pressure and the hot and therefore soft asphalt blisters. Traffic over the roof surface will easily break the blisters especially during cold weather when the asphalt is less flexible.
A roof covering of chips and stones will reflect sun heat and protect the felt and asphalt from decaying.
Metal clad and asphalt shingle pitched roofs leaks are particularly difficult to survey with thermal imaging equipment because of high reflections of sky temperatures, nearby buildings and structures etc.
Thermal imaging can pinpoint rising and penetrating damp in buildings immediately by providing a complete picture of the moisture. In most cases, the characteristic shapes and trails will identify direction of travel and the source of the ingress.