The camera sometimes lies

Thermal imaging may be the latest technology on the block, but can you tell the difference between a pretty picture taken by an untrained operative to back up a PR spiel and a professional thermographic image? Unfortunately, there is a raft of information about thermal imaging that is a long way from being true. This article will, I hope, give readers some insight into the facts.

Let’s take a minute to look at what thermal imaging cannot do. It does not look through things and tell you what is on the other side. In Alien, when Sigourney Weaver sees an alien through a sheet of steel, that is pure Hollywood. What you see in a true thermal image is an analysis of the heat being transmitted by the nearest surface. So, if you are looking at a building with glass balustrading at certain points, the camera will only register the parts of the building that does not have the balustrading in front.

The next thing to consider is the heat differential between the inside and outside of a structure. This needs to be at least 10-15ºC to allow a good thermographic survey to be carried out – anything less and it will not be possible to interpret the picture.

There are other things to take into consideration, such as damp surfaces, the subject composition and reflections. You cannot thermally survey stainless steel structures correctly, even on a dark night, as there is just too much reflection from the structure.

So what can thermal imaging do? The camera can tell you where heat is leaving a building, track water ingress, show if there is a failing in tanking integrity and how well the roof has been constructed. It can show robust details compliance, insulation integrity and leaks. It can tell you if there are hot spots in electrical installations and if the heating system is working correctly. You can, with the right training and a high-specification camera, tell how much gas is in a double-glazed unit and if there is a possibility that it is failing. So all in all, it’s a pretty clever bit of kit.

So why should you be careful? Well, there are a large number of thermal cameras in the field from various manufacturers and not all are being used as designed or with the correct training. The British Standard states that to carry out a quality thermal survey, the minimum equipment requirement is a 240 x 320 pixel camera. Anything less is what is termed as a “tool bag camera”, only capable of doing a quick check to detect an anomaly, not to give sufficient detailed information that a report could be based upon.

You cannot thermally survey stainless steel structures correctly, even on a dark night, as there is just too much reflection from the structure

Remember, you will be expected to pay good money for the operator’s service, and it matters not one jot how cheap it is if it is not accurate. Professional thermographers are well trained and have their cameras serviced and calibrated every year.

Now let’s consider the person behind the camera. Like all things new, there will always be the chancer – get the camera, turn it on, get a half-fuzzy picture and blag the rest. You know the type: laying carpets last week but the old back is giving them trouble so suddenly they’re doing thermography.

A good thermographer will be a construction professional – a qualified building surveyor is a good start. They will know what they are looking at and will be able to discuss anomalies with a good knowledge base. The next thing to look for is thermographic training. The minimum is level one and, if they are not a chartered building surveyor, a recognised building surveying qualification and/or level two building thermography from a recognised provider.

In the UK, there is a core of highly qualified themographic building surveyors who will always take your calls and give you good advice. It is not a black art, as was once put to me but, in the hands of a trained professional, it is capable of identifying defects without tearing down walls.

Rod Appleyard is a chartered building surveyor specialising in the forensic investigation of defects in fenestration and building envelopes. He can be contacted on 07785-232934