How to carry out a Thermal Building Survey

Thermal Building Survey | The cold roof in this image is displaying heat loss and should be investigated for thermal anomalies.
April 20, 2022
A thermal building survey is a non-invasive way, under the right conditions, and using thermal imaging cameras, to identify thermal anomalies in the structure of a building. FLIR (Forward Looking InfraRed) cameras convert infrared radiation into imagery that shows the distribution of temperatures across the image. All bodies with a temperature above Absolute Zero (-273°C) emit electromagnetic radiation, a thermographic survey carried out using a thermal imaging camera can detect infrared radiation invisible to the human eye.

What can an Infra-Red Survey Identify?

An infrared thermographic survey can be a valuable method of carrying out a non-invasive thermal inspection of buildings. An inspection of this kind can help to identify a wide range of thermal anomalies including water ingress, dampness, heat loss, air infiltration, cold bridging, and missing or degraded insulation. Thermal images will show you thermal inconsistencies that are not visible to the naked eye.

How to carry out an effective Thermographic Building Survey?

To carry out a successful thermal building inspection certain criteria must be met and specific procedures to be followed. Depending on the purpose of the survey, the criteria may change. As an example, a solar panel survey is carried out during sunlight hours, whilst a building fabric survey must be carried out at least two hours after sunset. Depending on the type of survey you are carrying out, you should ask a specialist thermographer for the correct conditions required.

What Reasons would I have for getting a Thermal Survey?

There are many reasons that you may want a thermal survey carried out at your home or workplace. It may be that your home is cold, and you feel that your thermal comfort has been compromised. You may book a thermal inspection for your house as you would like to reduce your carbon footprint, as according to the Climate Change Committee over 40% of all UK emissions come from our homes. You may be worried about the build quality of your home and worry whether your housebuilders followed best practices on each element of the build. It could be that with the rising energy prices, you want to identify if you can save energy, which would save you money and reduce your carbon footprint. Whatever the reason for carrying out a thermal survey, whether it is internal, external, or a combination of the two, clients need to understand that we can tailor reports to suit their needs. Read more about thermal surveys here.

Booking a thermal survey

Once you have had discussions with your thermographer and agreed on the type of thermal building survey, then you have to agree on a date. In the UK this can be a difficult task in itself with the unpredictable weather that we have. You will have been informed of the conditions required for your inspection, and then we have to see the external conditions align to make the survey happen. As an example for a standard internal/external domestic property survey, we would require
  • 10° minimum temperature difference from inside to out
  • Large items of furniture moved away from external walls during the heating of the property
  • Wind Speed at less than 5 m/s
  • External Building Envelope dry (ideally no rain in the previous 24 hrs)
  • Internal Ambient air temperature within 10° a minimum of 24 hours (ideally up to 72 hours)
  • Open all internal doors
  • Take down heavy curtains during the heating of the property
  • Close all external windows and doors
Now that the parameters for the survey have been defined, it’s best to understand why we need these measurable factors. The 10° difference is required as according to the second law of thermodynamics, heat always seeks cold, never vice versa. If we don’t have a minimum temperature difference from inside to out, then the thermal cameras are unable to detect any thermal variances. If it’s the same temperature inside to out, nothing can be picked up by the thermal images. Moving large items of furniture, such as couches away from external walls, allows airflow circulation around the rooms. This must be done once the internal heating has been turned up for the survey. If this is done on the thermographer’s arrival, the warming convective currents will not have had time to circulate effectively, and this could result in the misidentification of thermal anomalies. The windspeed should be less than 5 metres per second for the external building envelope. According to Newton’s Law of Cooling, if the windspeed is more than 5 m/s then the elevation will rapidly cool, which could give a false thermal reading as if the elevation is cooled rapidly, thermal equilibrium could apply. Rainwater against a building envelope can also rapidly cool the structure, rendering any thermal inspection null and void. Surfaces need not be exposed to solar radiation for at least 1 hour (preferably up to 6 hours) before the survey. This is because during daylight hours, the building envelope can be heated by solar radiation, and after sunset, the ambient air rapidly cools allowing thermal differences to be measured. Internal Ambient air temperature needs to be maintained for an absolute minimum of 24 hours (ideally 72 hours) before the survey. The reason for this is when the heating is turned on, the air is the first thing that is heated, and we need to “thermally load” the structure to get the best readings. We are trying with the heating on to heat the building fabric rather than the air inside the building. All internal doors should be opened to allow the convective airflow currents to circulate easily around the structure. Like with the heavy furniture above, curtains should be taken down where possible to aid airflow and reduce the chance of thermal bridging. All external windows and doors should be kept closed before the survey to allow the building fabric to be heated to the desired temperature. Read more about thermal building surveys here.

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