| Thermographic Testing
Why Infrared Thermal Imaging Surveys
Air Pressure Testing have many years experience of carrying out thermographic
surveys and can offer clients advice at an early stage as to the most
productive method to carry out a thermographic survey.
Air Pressure Testing wide ranging technical and practical experience of
building technology, design issues and potential faults in buildings allows
us to give a high level of service both in carrying out the survey and
interpreting the results.
Building thermography is a method of indicating the heat distribution
over the surface of a building envelope. This remote-sensing technique
can be carried out with minimal disturbance by one of our engineers and
allows qualitative detection of air leakage pathways and insulation discontinuities.
The survey will be carried out using an un-cooled thermal imaging camera,
which can measure temperatures to 0.1°C and displays the images and
reports in full colour. Air Pressure Testing uses a calibrated FLIR infrared
camera, which allows full analysis of saved images.
Thermographic Surveys are carried out to BS EN 13187:1999: Thermal performance
of buildings - qualitative detection of thermal irregularities in building
envelopes - infra-red method and BRE Report 176 - A Practical Guide To
Infra-Red Thermography For Building Surveys.
On-site Requirements For Thermographic Surveys
The following outlines the requirements for the above test. Areas of discontinuous
insulation will be more readily identified in these conditions:
• Drawings (plans and sections) and specification details regarding
the areas to be surveyed should be supplied prior to the survey taking
• The integrity of the building envelope should be complete for
• APT have assumed that the survey will be carried out from the
outside of the building, usually at night (or on an overcast day in winter)
when the weather is dry.
• It is important that the internal temperature of the building
is 10°C higher than the external
• If possible, the internal pressure of the building should be raised
by 10 Pascals by switching off the extract units
An hand-held infra-red sensitive camera records images of the subject
that are compared to conventional pictures of the same areas. "Hot-spots"
can then be related to features of the building and an informed view taken
of building integrity. Local/component thermography whilst a building
is depressurised can identify where air tightness needs improving.
Golden rules to ensure Part L is met
You must ensure there is a minimum temperature differential between inside
and outside the building of at least 10°C. This is usually achieved
by leaving the heating system turned on inside the building for 12 –
24 hours prior to the survey.
Carry out external Thermographic surveys after dark (or heavy cloud),
to ensure problems with sunlight warming up external surfaces can be ignored.
Ensure the weather is dry as moist surfaces play havoc with the survey
results. Beware items of plant emitting heat inside a building, as they
can affect the results.
Why use Thermographic cameras?
A thermal image makes it easy to identify areas of missing, misplaced
or discontinuous insulation.
It can also be used to identify air leakage paths if used correctly. Cold
air leaking into a building will cause cold patches on the surrounding
fabric, which can be identified from thermal images.
Can Thermographic surveys quantify air leakage?
No, but they provide a qualitative appreciation of the thermal properties
of a building envelope, quickly over large areas and display the results
graphically in colour. Spot temperatures are also measured which can allow
for later analysis of the thermal performance of building envelopes, again
especially useful in highlighting areas of misplaced or discontinuous
insulation, something Air Leakage Testing cannot
How can you interpret the thermal images?
A sound knowledge of construction technology and a sound knowledge of
the projects design (U values, emissivity of materials) allied with experience
of on site defects is required to identify the true cause of faults identified
on site. Particular care needs to be taken with regard to the emissivity
and reflectivity of surfaces. Surfaces with low emissivity (e.g. polished
steel), appear colder than their surroundings but are sensitive to reflective
heat from background sources e.g. equipment, lights, people etc.
When To Get Worried
If the thermal image of the inside face of a building envelope appears
to have a low surface temperature compared to their surroundings. Take
care to evaluate the results as this could be caused by;
• Missing or damaged insulation or maybe high levels of moisture
within the building fabric
• High levels of air leakage cooling the inside face
• Thermal bridging
• Evaporation of moisture from the internal surface
• Cold rooms inside the building cooling the surroundings
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