Understanding Thermal Imaging

We have many investigative tools available at our disposal in evaluating the overall condition of the houses we inspect, and one of those that some of our inspector’s use, is a thermal camera. All objects above absolute zero or 0-degree Kelvin (-276 degrees Celsius) radiate an electromagnetic signal in the infrared wavelength. This signal is transferred through the atmosphere and captured in an image in our digital thermal imaging cameras.

Contrary to popular belief the camera does not measure temperature, it records the wavelength the object emits in the electromagnetic spectrum measured at distance of 25.4 micron (that’s about 1/1000th of an inch) from the face of the object. The camera then converts this energy into a digital image of the object, we can then store and analyse this data using thermal signatures and patterns over time, and by measuring the objects temperature in relation to the ambient atmosphere.

This tool is handy when it comes to house inspections, but is really only useful when there is a minimum of 10-degree Celsius temperature difference between the inside and outside of a building. Generally, a visual inspection of the property should always be carried out prior to an infrared inspection, and imaging is best undertaken either early in the morning or at night to negate the effects of thermal gain.

Infrared Imaging is carried out on the exterior of a property first to give a general view of the exterior surfaces, and then a more detailed examination is undertaken of suspect surface areas inside.

When looking for moisture and water infiltration in properties it is important to note that it takes 4186 Joules of energy to heat 1kg of water by 1 degree, whereas 1kg of air requires only 1000 Joules. This is known as specific heat and is defined as the amount of thermal energy required to raise the temperature of a material by 1-degree C. The measurement of this number is expressed in Joules per kilogram- Kelvin the higher specific heat the longer it will take to heat. In the image below the wet plasterboard lining was cooler than the dry plasterboard lining as the temperature increased because of the specific heat required to increase the moisture laden plasterboard.

leak through plasterboard


Conversely an object with a high specific heat will also retain or ‘hold’ its energy much longer than an object with a low specific heat value.

So, when checking for moisture early in the day, the dwelling will generally heat quicker than any water or moisture contained in the framing timbers and appear as a ‘blue’ colour in the image; however, at night the stored energy from moisture will take longer to cool because of its high specific heat and will appear ‘pink’ as a comparison in the image that the thermographer captures.

The correct operation of a thermal camera requires a great deal of skill and training. NZ House Surveys is proud to have several qualified thermographers who have undertaken studies and passed the necessary exams to be able to competently assess the thermal patterns of your next house.

Call us today for your building inspection needs, phone 0800 487 884

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