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Thermal imaging of Listed and historic buildings

It never ceases to amaze me how many Chartered Surveyors and self styled Listed Building Surveyors start using buzz words like thermal imaging, and buying a shiny new imaging camera to make pretty pictures of buildings.  It is just not that easy. One chap I know publishes pretty pictures of heat loss in windows, and keeps copying our technical information - talking about finding things with his camera.  At one level, imaging can indeed find hot water pipes - and yes, it can show you, on a cold day, that your windows are cold.  You don't need to be a rocket scientist to know that..

We use imaging to look at much more subtle variances in heat patterns within buildings. The most important use of these things is to pinpoint areas that are likely to be susceptible to interstitial condensation.  You don't need a very big difference in the temperatures of a wall for this to happen - a drop of half a degree is enough for condensation to start forming, and for moisture to be trapped into a wall.  Our cameras are usually connected to the thermo hygrometers, so we can analyse the atmospheric conditions, and use these to predict where moisture may form - to plan and map condensation weak points, and predict damage before it happens.  By mapping buildings in this way, we can assess overall heat loss characteristics, relate them to moisture levels and atmospheric conditions, and help owners to better insulate, heat and manage their home.  Many of the scientific details used in this work are derived from our own extensive scientific research, coupled to the BRE work mentioned elsewhere in this site. I use thermal imaging a lot with timber framing to map weak points in the frame and assess where we need to prevent water ingress and seal the joints.


Kentish Farmhouse - thermal imaging to predict condensation

In this particular property,  a farmhouse in Kent, the external walls were a mix of oak timber framing and masonry. The internal floor was concrete. 

There were damp issues at low level in a number of areas to the external walls. 

There were some basic building defects which were causing some of the dampness. These defects were leaking gutters, raised ground levels externally and some very hard impervious cement render internally which was trapping moisture in the walls. Fixing the basic defects is easy to specify and will be relatively cheap. Fixing gutters and lowering ground levels in most instances is a cheap and easy fix. However, what about the concrete floor and impervious cement plaster internally? Ideally these would be removed but this will be very expensive and is it really necessary? 

This is where the imaging camera comes in very useful in conjunction with other tools, and can often help inform suggestions to remedy problems. In an ideal world there would not be any concrete floor slabs and cement rendered walls in traditionally built properties (excluding of course the Concrete late Victorian house in Dulwich, but thats another story!!). In the real world, sometimes we need to make the best of the situations as we find them according to peoples budget, and the buildings ability to cope with any given level of moisture. 

We record the relative humidity, absolute humidity and dew point inside the buildings we survey. This gives us very important information regarding the levels of moisture in the air, and the structure. 

The “Dew Point” is the temperature at which condensation will occur. We can use the Thermal Imaging camera set colours at the dew point to identify only areas that are at risk of condensation. In the photos attached the blue colour is used as an example to identify areas that are at risk of condensation forming.

The key thing to note here is the areas that are vulnerable to condensation in the examples below are set as around 14 degrees. This is because the humidity was very high in the house and the dew point was around 12 degrees. If the humidity is lowered, then the dew point will rise and the areas become less vulnerable to condensation. 

We use the Thermal Imaging camera along with other tools (such as Carbide meters to test actual moisture content of the walls, and Thermo Hygrometers to test humidity and dew point) to assess the walls.  This enables us to give a sound and reasoned judgement on what needs to be done and why. In reality before we had thermal imaging cameras we were still able to make an assessment of the building, but it relied solely on our own experience in looking at these issues and was not hard evidence based. Now we have nice pictures and evidence to show. 

In this instance, we recommended fixing basic building defects and reducing humidity, but we did not recommend full removal of the concrete floor slab and renders. We found through testing that moisture was mainly confined to the surface of walls through condensation build up, and basic building defects such as leaking gutters. 

A proper diagnosis has saved the building owner some time and money in doing unnecessary work, and has given them a simple fix to a simple problem. Importantly when we carry out a survey, it also gives us a good chance to explain to clients, with pictures and explanations what is going on, and why.

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