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Roofing : US Postal Service, Monmouth, NJ

Infrared Analysis
US. Postal Service
Investigation: 4/11/96

Table of Contents

  1. Abstract

  2. Profile

  3. Roof Evaluation

  4. Roof Illustrations



The purpose of the infrared survey is to detect and define moisture damaged roofing components. The survey utilizes thermal imagery to identify moisture within the roof system, without the use of destructive testing.

The basic tool of ABACUS GROUP LTD. Infrared Roof Survey is the Agema Thermovision 450 Infrared Thermal Measurement and Imaging System, using the state of the art Electro-optical scanning mechanism, the new SPRITE infrared detector, video interface and control electronics and microprocessors for video output. The infrared camera converts electromagnetic thermal energy radiated from an object into electronic video signals. These signals are amplified and transmitted to the video processing part of the camera where the signals are further amplified and the resultant image is displayed on the viewfinder. The camera senses the intensity of thermal radiation from the roof surface, and displays a monochrome image whose density corresponds to the radiation intensity. The radiant energy levels are interpreted as surface temperatures.

Water enters the roof system by means of holes, splits or faulty flashings, causing the roofing components (i.e.,. decking, insulation) to become wet. The wetter areas store more heat from daytime solar loading and remain warmer at night. Reduced thermal value of water damaged insulation and/or decking materials also allows for heat transfer of interior energy through the wet components areas during the colder months. It is this thermal radiation of water present in the roof that the infrared camera records. The hot spots are visible on the surface of the roof when viewed through the infrared camera.

Moisture entering the roof system at penetrations, base flashings, and masonry walls that does not affect the insulation will not be detected by the infrared camera because the moisture runs directly into the building interior, leaving the insulation unaffected. Masonry walls can be scanned for moisture entrapment under certain conditions. For more information on masonry wall scans, contact ABACUS.

The roof top is scanned at night. Scanning at night allows for sufficient cooling of the roof surface and eliminates solar reflection resulting in a more accurate scan.

Upon request, certain portions of the thermal information obtained during the scan can be videotaped for further analysis. This information is later digitized using the new Data Translations High Resolution Frame Grabber, which digitizes the real-time video signal for further processing by the IRIS Image Processing Computer System.

The thermal image signal is broken down into a 16 color temperature scale, and temperatures/colors are assigned to the radiational intensities of the image. The information can now be presented as colorized thermograms, with different colors representing different roof surface temperatures. Variables that can affect the thermal radiation include wind velocity, cloud coverage and material density. A color bar along the bottom of the thermograms indicate temperatures in ascending degrees with warmer areas (typically the wettest areas) at the right of the bar. Also included are Black and White Thermograms that depict the same image seen and recorded on the roof during the survey. Corresponding visible light photographs help to orientate the thermograms, as well as give clues to water entry points.

Areas of wetness obtained, if any, are marked on the roof surface with yellow spray paint during the IR survey. The areas indicated represent findings identified during the IR survey. Repairs to the roof system are recommended to be performed as soon as practical. Please note that the findings of the infrared moisture survey can only be accurate and representative for the time of the moisture survey. Additional moisture intrusion into the roofing components upon completion of the survey will typically tend to enlarge the areas of subsurface moisture identified.

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Confirmation of subsurface moisture at anomaly locations was initially made by locating the membrane punctures, and physically detecting moisture within the insulation.

BUILDING: U.S. Postal Service Monmouth Processing and Distribution Center, Monmouth, NJ

SCAN DATE: 4/11/96

SQUARE FOOTAGE EXAMINED: approximately 300,000 Sf




ROOF COMPOSITION: steel decking
isocyanurate insulation ballasted EPDM single ply membrane

CONDITIONS: Skies- clear
Winds 1-3 mph
Relative Humidity 45%
Outside Air Temperature 55 degrees F.

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The infrared roof moisture survey was conducted in an attempt to locate and define areas of moisture damaged roofing components on the U.S. Postal Service Building in Monmouth, NJ. The survey was conducted on April 11,1996 at approximately 6:00 p.m. Scanning during the night hours is necessary for certain temperature differentials to take place, allowing the thermal anomalies to appear. The infrared camera views the entire roof area. Large portions of the roof can be scanned at once, and problem areas are easily isolated and outlined with permanent marking paint (A.P.W.A. Yellow).

System calibration was made based on thermal imagery typical for moisture affected insulation patterns. Historical readings of similar type roofing components moisture patterns were calibrated with thermal intensity readings taken during the survey for accurate anomaly definition.

General atmospheric conditions were acceptable during the survey. Solar loading was accomplished with substantial sunshine during the day. An interior to exterior temperature differential was also recorded.

Scanning the roof regularly (at least once a year) can assist in a planned maintenance program that identifies moisture damaged roofing before they become enlarged and more expensive to repair. Yearly scans can increase the service life of any roof system by identifying exact locations of water damaged roofing and leak points, which can then be accurately and efficiently repaired.

Eleven (11) thermal anomalies were detected with a total area of 156 square feet. Four (4) anomalies are located on the lower roof section, and seven (7) on the upper roof.

The cause of moisture leakage appears to be from membrane punctures.

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During the infrared survey of the roof, a random selection of thermal data was recorded on videotape and later processed to create the following thermograms. Each set of photographs depicts one sample area as a colorized thermogram, black and white thermogram, and a visible light photograph. The video taped data is also available for viewing upon request. The thermal data recorded is for illustrative purposes only.

Anomaly #1

a. Colorized Thermogram - This thermographic set depicts one wet insulation area as white and yellow. Red and black indicates dry roofing components.

b. Black and White Thermogram - In this type of thermogram, wet insulation appears as white. The thermal energy within the moisture affected roofing transmits through the heavy ballast stone surfacing.

c. Visible Light Photo - A small puncture in the membrane was found within the painted outline.

Anomaly #3

a. Colorized Thermogram - A second, smaller wet area is also seen below a walkway tread. The anomaly appears as white..

b. Black and White Thermogram- Note the paint markings, seen cooler on the roof surface (black lines).

c. Visible Light Photo - To repair, the treads must be removed.

Anomaly #10

a. Colorized Thermogram - A small puncture in the membrane creates this anomaly, located in the filed of the roof.

b. Black and White Thermogram - The white area is the water damaged insulation. With each winter season, the anomaly will enlarge.

Visible Light Photo - Anomaly #10 appears similar to #11, which was not recorded during the survey.

The colorized thermogram depicts moisture affected roofing components, if any, as changes in color. The colors white, tan, yellows and greens, generally indicate the wettest insulation or decking. The color dark blue indicates wet or damp substrate. These colors are usually found at the edges of the anomaly area, or in areas not yet saturated. Reds and black indicate dry roofing substrate.

The black and white thermogram depicts moisture saturation conditions as shades of grey. The whitest areas generally indicate the wettest substrate. The blackest portions indicate dry roofing. These calibrations were set using readings of wet and dry roof components. The white portions of the thermogram are created by the wet roofing, which emits higher levels of infrared thermal energy than dry materials, when scanned during the night.

The visible light photographs are generally taken from the same location as their corresponding thermograms and depict a similar field of view.

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