Innovation In Structural Investigation


GBG utilizes a combination of Non Destructive Testing Techniques, including Infra Red (IR) Imaging and also hand-held moisture meters to establish the existence and extent of trapped moisture beneath the waterproof membrane; typically within roof insulation.

All investigative work carried out confirms to ASTM C1153–97, (Location of Wet Insulation in Roofing Systems using Infrared Imaging) and can therefore be used by roofing contractors to assist in extending the warranty period of a roof and also by Structural Engineers, Architects and Designers when carrying out general condition assessments and submitting repair recommendations.

Diurnal heat flow into and out of a structure is effectively a constant, with some local differences dependent on material / finish and thickness. Moisture within insulation layers will interrupt the flow, altering the thermal response of the surface to environmental change; the thermal capacity of wet insulation is greater than that of dry insulation and as such absorbs more solar heat energy, and cools down at a slower rate. Therefore, areas of wet insulation will appear hotter (lighter) in thermal images (See Images Below).

Following an initial visit to the building to assess it’s suitability for this type of investigation, a team of two GBG site engineers is required to carry out the survey. In order to maximise thermal contrasts between the interior and exterior of the building and therefore to obtain the best conditions for mapping wet and dry areas of roof insulation all survey work is carried out after sundown. Initially, a scan of the entire roof is performed using a hand held thermal camera, typically (and most effectively) from elevated vantage points such as scaffold towers or stairwell bulkhead roofs. The second team member, positioned directly on the roof, delineates any thermal anomalies identified by the camera operator.

Once completed, the team visually inspect all of the marked areas, identifying and recording any surface features that could have caused the thermal anomaly. A hand-held, non invasive moisture meter is then used to provide additional assessment as to the moisture content of each highlighted zone in order to corroborate the IR results.

The data collected by GBG is presented in a comprehensive report with appropriate recommendations as to the next stage of inspection and repair. The information supplied is then used by Structural Engineers, Architects and Designers in recommending remedial measures or full replacement of the built-up roof assembly.

ASTM C1153–97 provides strict guidelines for performing this type of investigation. Several factors have to be taken into consideration both before arriving on site and whilst analysing the data off-site. The weather is monitored for several days prior to confirming a start date, to ensure that little or no standing rain water is present on the roof surface during testing. Wind speed, cloud cover, outside temperature ranges and temperature differentials (inside / outside) are all monitored and recorded to ensure that a suitable thermodynamic environment exists, which will allow an effective and accurate assessment to be achieved.

Scanning of a roof to identify and map wet insulation is just one application of thermal imaging. GBG also utilizes this technology and various other testing techniques to provide a range of condition information including: Tracking of water infiltration / Leakage through a building / ASTM E1186-03 - Air Leakage Site Detection in Building Envelopes and Air Barrier Systems / Façade Assessment – Mapping condition of masonry and embedded steelwork.

When operated and analysed by experienced professional’s variations in thermal responses can yield all sorts of useful information - Please call us at our New York Office and find out more.

7104 Fort Hamilton Parkway
2nd Floor, Brooklyn
NY 11228-1017
Tel: 718 238 7575

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