Table 1. A classification of NDT of assessing moisture content in building materials
Method
Investigation Depth
Type
Constraints
Measured Parameter
Indicator paper method
Surface
Qualitative
Indicates only the presence of moisture
Change in indicator paper colour in influence of damp material
Infrared thermography (IRT)
Surface
Qualitative
Nuclear magnetic resonance
Up to 20mm
Quantitative
Moisture meter
Up to 30mm
Holographic radar
Up to 200mm
Sensitive to Surface temperature variation environmental condition
Presence of iron within the surface, organic Electrical impedance materials Presence of iron within Quantitative the surface, organic Electrical impedance materials Applicable only on flat Amplitude modulated by phase Qualitative surfaces variation
Building performance evaluation guide (2021) suggests a site visit/ and or conversation with occupants to check for signs of visible condensation and mould growth. A study on understanding whether building fabric introduces high risk of thermal bridging, discontinuity of insulation at junctions and penetrations is also a must. Assessing thermal bridges is suggested as an important factor as these are not just a location of heat loss but can also lead to condensation and mould growth. It also suggests to study both, inwards and outwards moisture flows if moisture levels are too high over long periods. Inwards moisture flow relates to moisture generated indoors (toilets, other wet areas), whereas outwards moisture flows relate to moisture from outdoor air, rain, and ground. A further inspection can be made on how the envelope is protected from water damage. Furthermore, thermography can be used to identify cold spots on cold cloudy days (preferably early morning/ early evening). These could indicate either air leakage or thermal bridging. However, this is only qualitative and would not solve all issues. BS 7913-2013 Guide to conservation of historical buildings states that in case of evidence of moisture in the building fabric, the internal environment should be examined for possible sources of condensate and appropriate ventilation measures should be applied. To mitigate surface condensation, CIBSE AM13: 2000 suggests the use of moisture sensors to prevent condensation. They may automatically trigger switching ‘on’ a mechanical system to dehumidify the space.
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