Qualitative timber structure assessment with passive IR thermography. Case study of sources of common errors

The use of infrared thermography, a non-destructive technique for detecting structural failures or hidden defects, has become ever more common in the last 10 years. The combination of its growing popularity, the relatively small price tag on low-resolution devices and the lack of operator experience has fostered significant errors in the interpretation of the resulting images. This paper describes the use of infrared thermography and imaging to assess the condition of a historic timber-roofed building in Madrid, Spain. It aimed primarily to determine the utility of thermographic techniques in the detection of flaws such as cracks, moisture content and detachment. On the other hand, the limitations of IR techniques and the errors most commonly committed in interpreting the results must be identified to determine how to avoid misleading interpretations. The survey methodology deployed here followed a procedure established for earlier studies of historic buildings in which preliminary fact sheets were drawn up to determine the areas of the building’s structural members most in need of assessment. Changes in timber properties and weather-mediated moisture content were identified on the grounds of material emissivity using passive thermography. Active thermography is recommended to detect internal flaws.