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Thermal imaging report guide (NF86)

Thermal imaging has been used for some time to give a non-invasive ‘window’ at various stages of construction. It can show the thermal performance of the external walls, roofs and internal services.

NHBC Foundation’s latest guide, prepared in collaboration with BSRIA, looks at this increasingly useful technology. It identifies what a good thermographic survey should include, gives advice on good practice when preparing for and carrying out a survey and highlights what makes a successful report.

The guide gives examples of typical thermal imagery and identifies the most common issues that can affect the accuracy of a thermal imaging report if the survey isn’t interpreted correctly. These include:

Using a specialist thermal camera.

This detects infrared radiation which is electromagnetic radiation (EMR) with longer wavelengths than those of visible light and therefore, generally invisible to the human eye. The correct settings of this specialist camera are crucial for an accurate survey.

Using a qualified thermographer.

The interpretation of a report is key, it is recommended that the person carrying out a thermal imaging survey is suitably qualified, these experts are referred to as thermographers.

Suitable weather conditions.

At the time of the survey are vital in achieving an accurate picture of the thermal performance and, ideally, there should be no significant changes in external temperature during the 24 hours before the survey, nor should it be raining or windy during the survey. Additionally, the survey should only be conducted when there is an adequate temperature difference between inside and outside of the property.  

Summary of content

This guide contains 6 main sections:

    1. Introduction: what is thermal imaging?
    2. Taking and reading thermal images: looks at the equipment needed to take a thermal image, how the camera converts the image, the importance of the temperature scale and typical colour palettes used in thermal imaging – their advantages and disadvantages.
    3. Interpreting a thermal image: looks at what a thermal image of a building will show typically, how to recognise faults, the limitations of thermal imaging, the importance of weather conditions at the time of the survey, heat loss through the building fabric and misleading features in the building fabric.
    4. Common potential faults found using thermal imaging: looks at what a potential fault could be and compares images in 11 scenarios including:
      • Gable wall
      • Perimeter of ground floor
      • External wall – timber frame construction
      • French doors
      • Windows
      • Dry lining
      • Ceiling – downlighters
      • Ceiling – at junction with gable wall
      • Ceiling – at junction with external walls
      • Dormer window
      • Underfloor heating
    5. Typical variations in thermal images: looks at common areas where heat loss may be indicated but are not usually indicative of a fault,  looks at typical external thermographic images and thermal imaging used with airtightness testing.
    6. Ensuring a good thermal imaging survey: identifies thermal imaging standards and thermographer qualification requirements, identifies what a thermal imaging survey should include and the different types of thermal imaging survey, looks at what to do if a potential fault is identified and what to be aware of when checking through a report.