Applications for Infrared Thermography as an NDT Method for Buildings by Greg Stockton Manuscript

7/23/2019 Applications for Infrared Thermography as an NDT Method for Buildings by Greg Stockton Manuscript

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Applications for Infrared Thermography as an NDT Method for

Buildings

Gregory R. Stockton

Stockton Infrared Thermographic Services, Inc.

www.StocktonInfrared.com 8472 Adams Farm Road

Randleman, NC 27317-7331

(800) 248-SCAN (toll-free)(336) 498-GREG (voice)

(336) 689-3658 (cell)

[email protected]

Abstract

When one wants to construct a building, he/she first hires several prime contractors tomanage the construction. An architect is retained to design the building, a structural

engineer to design a sound structure, and a general contractor is hired (by bidding or

negotiating) to oversee construction and make sure that the project runs smoothly, on timeand on budget. The general contractor then subcontracts to building trade contractors, such

as: site work, foundations, steel, masonry, electrical, plumbing, heating, ventilation and air

conditioning, roofing, painting, fixtures, finishes and furnishings. All these subcontractors

are given a set of plans, drawings and specifications to follow to construct the building sothat it meets the building codes and satisfies the owner’s needs.

During the construction process, tests are performed to ensure that the design specificationsare being met. These tests can be cursory and quite subjective in nature. Sometimes the

plans are changed in mid-project because the owner decides to make a change to the

building. At that time, a change order is executed and the building is retrofitted or de-constructed in part. This destructive activity may reveal faults in the building that were not

brought to the attention of the owner during the original testing. At that moment, the owner

may call into question the results of other tests and even the integrity of the building itself.This paper discusses applications for NDT (non-destructive testesting) of buildings using

infrared thermography to ensure that the design specifications are met.

1. Introduction

Although some of the very first applications for infrared thermography were buildinganalyses applications, other applications have surpassed building IR in popularity over the

last 20 years. But, building owners are increasingly concerned with the costs and quality of



construction, and the efficiency and operating costs of their buildings. Infraredthermography can be used as an effective building quality assurance tool during

construction, so that repairs can be made without destroying the building or delaying the

building process.

2. Understanding Infrared Testing Methodology for Buildings

Infrared imagery is often a grayscale picture whose scales (or shades of gray) represent the

differences in temperature and emissivity (opposite of reflectivity) of objects in the image.

As a general rule, objects in the image that are lighter in color are warmer, and darkerobjects are cooler. No object in the images is detected via visible light wavelengths (400-

700 nanometers) rather, only from thermal infrared wavelengths of 3000-5000 nanometers

or 8000-14000 range. Lights and other relatively hot objects are very evident, but as aresult of their heat, not their light emissions.

When an image is taken with an infrared camera, it is often recorded onto videotape and/ordigitally saved to on-board media. The image may be then modified in a number of ways toenhance its value to the end user. Usually, building images are digitized, saved and

analyzed with specialized software. The images are then adjusted for color, contrast and

brightness before being scaled and placed in a report.

At different times of the day and night, building components show differences in

temperature because of differences in mass, moisture content and heat loss because heatfrom thermal changes radiates from these areas at different rates. During these thermal

transient conditions, thermographers can scan the building with a sensitive infrared camera,

detect the sources of heat and record them for later analysis. Since infrared thermographers

use real-time imaging and recording IR equipment, they can immediately determine if andexactly where any problems exist. Before infrared thermography, determining the

placement of building materials in-situ in a building was a painstaking and destructive

undertaking.

There are four types of buildings by use:

• Residential - houses and apartments dwellings of all types

• Commercial - office buildings, retail stores, malls

• Industrial - manufacturing facilities and plants

• Institutional - college and universities, hospitals, government buildings

To be an effective tool, an infrared thermographer must know the limitations of the imager,the way that buildings absorb and radiate heat energy, and the best time to perform a given

IR survey. He/she must have an imager capable of finding and documenting problems andmore importantly, a very good understanding of building physics. Building IR applications

can actually be some of the most demanding on imager thermal sensitivity and spatial

resolution, the two most important factors in an imager’s ability to focus in on sometimes

physically small and/or thermally miniscule problems. For example, there is a different



methodology for surveying the wood framing, missing insulation, heat loss, air-leakage andmoisture intrusion in the same building. IR can only detect surface temperatures, but

differences in surface temperatures and the patterns they leave (IR signatures) can indicate

what is going on inside the building.

Building IR applications can actually be some of the most demanding on thermal imager

sensitivity and spatial resolution, the two most important factors in an imager’s ability tofocus in on what can be physically small and/or thermally miniscule problems on a giant

object. Coming up with effective techniques and good timing to perform these surveys also

presents a challenge. For example, there is a different methodology for surveying the

framing, missing insulation, heat loss, air-leakage and moisture intrusion in the same building. IR can only detect surface temperature differences, but the patterns that these

differences leave (IR signatures) can often indicate, what is going on within the building to

a very high degree of confidence.

3. Applications for Building Thermography

Below, some building IR applications are discussed and example imagery shown:

3.1 Construction Defects

Liability is a real issue for sellers, buyers and insurers. The costs of construction, repairs

and renovation are increasing dramatically as owners bring construction lawsuits againstthe contractors. Perspective building owners are increasingly concerned and IR can be used

as a building quality assurance tool during construction, so that repairs can be made without

destroying the building or delaying the building process. Since all building materials will

absorb, retain and radiate heat energy at a different rate, building components can bechecked for the quality of installation using IR.

3.2 Structural IR Surveying of CMU Walls

CMU (concrete masonry unit) walls are erected on nearly every street corner as malls,

schools, warehouses, retail stores, etc. These walls often have reinforcing bars imbedded ingrout-filled cells as a critical structural component. By allowing the wall to absorb energy

during the day and watching the heat energy dissipate at night, the building infraredthermographer can use the “picture” of the heat from the wall, to define exactly where the

grouted cells are and where they are missing (see Figure 1). A time vs. temperature graph

of a typical CMU wall (see Figure 2) over a 24-hour period shows how grouted and non-grouted areas heat and cool at different rates. Unfortunately, all walls cannot always be

surveyed under ideal conditions. For instance, during some times during the year, because

of the orientation and low angle of the Sun to the building, some outside walls do notreceive direct sunlight at any time during the day. Inside walls never receive any direct

sunlight but often can still be surveyed. Also, the walls can be heated by using heaters (see

Figure 3) to achieve the desired delta-T.



Figure 1. Visual and infrared image of a CMU wall showing a bond beam (horizontal

reinforcing) incomplete on the left side of the man door.

Figure 2. Time vs. Temperature Graph of a CMU wall over a 24-hour period.



Figure 3. Visual image of a CMU wall being heated, with cart-mounted IR imager in

the right foreground.

3.3 Rodent and Insect Infestations

Rodents (Figure 4) inside a building can be tracked-down because they are warm-blooded.

Insects, especially termites (Figure 5) damage millions of dollars worth of buildings eachday. The decrease in mass left by these building materials-destroying creatures can be

quantified by using infrared thermography.

Figure 4. Visual and infrared image a mouse inside the wall.(Images courtesy of Jon Grossman, High-Tech Inspections, Inc.)



Figure 5. Visual and infrared image of a church vaulted ceiling with termites.

3.4 Quality Assurance of the Thermal Envelope

The proper installation of thermal insulation and air barriers can also be checked usinginfrared thermography (see Figures 6, 7, 8, 9). Every building owner wants to get their

money’s worth and also know that they are getting the building that they designed and are

paying for. Other methods of testing; on-site testing companies, installing inspection ports, performing destructive testing and X-raying are ineffective, inefficient and/or too

expensive. Infrared thermography can be used on the job site as an inexpensive, efficient

and effective way to improve the quality of construction.

Figure 6. Infrared image of a convention center wall with missing (black) and

misplaced (dark gray) fiberglass batt insulation.



Figure 7. Infrared and visual image of a CMU wall showing that grouted, empty and

insulated cells have a different rate of heat dissipation.

Figure 8. Visual and infrared image of a new residential building with air leakage and

missing insulation.



Figure 9. Infrared and visual image of an office building wall. Taken when outsidetemperatures were low, the heat from the misplaced insulation in the interstitial space

above a suspended ceiling, shows the reverse heat pattern from the missing insulation.

3.5 Stucco Delamination

Stucco is an exterior plaster or interior plasterwork applied directly to the framed structure

of a building. There are two types of stucco; cement and synthetic. Cement stucco has beenused for thousands of years. It is a mixture of Portland cement, sand and lime. Synthetic

stucco or EIFS (exterior insulation and finish system) is a combination of foam boardinsulation and several coats of acrylic polymers.

Because both types of stucco are layered onto a building, there is a possibility that thelayers will delaminate (see Figure 10) from one another or from the building. Because

synthetic stucco has tightly placed high density foam insulation as one of the components,

there is a possibility that the building is too well insulated or that it will not “breathe” well,trapping moisture inside the walls. With both types of stucco, the quality of the installation

can be monitored using IR NDT methods (see Figure 11).



Figure 10. Infrared images of a new condominium with stucco delamination shown.



Figure 11. Infrared images of a new condominium with stucco, missing insulation.



3.6 Quality Assurance of the Moisture Envelope

In buildings, excessive moisture can create huge problems, like mold, mildew and

deterioration of the building itself. IR thermography can effectively be used to find

moisture...but not mold. [Mold does not exhibit an exothermic reaction that can be seenwith an infrared camera walking around a building.] Moisture in buildings is usually caused

from the installation of wet building components, water intrusion and/or a faulty thermal ormoisture envelope. Water intrusion implies that the building has been compromised and

that water is coming from somewhere; either from the roof, the walls, the basement or from

a mechanical or plumbing leak. Moisture inside the structure is often the result of any one

or a combination of factors, such as water intrusion problems, thermal envelope problems,ventilation problems and/or HVAC system problems (see Figures 12, 13, 14). High relative

humidity inside is common, as are badly designed, poorly constructed and poorly

maintained buildings. Preventive/predictive maintenance of buildings is very uncommon,therefore most IR NDT is performed on buildings with problems.

To reduce moisture in buildings, all buildings and all building components should be keptdry during the construction process. All buildings should be also be tested within a few

months after construction or major renovations to the structure, the thermal envelope, themoisture envelope and/or the HVAC system. Also, pressure and humidity in the building

should be constantly monitored. In many cases, damage to the building is caused by

insufficient ventilation and/or an under- or over-designed HVAC systems. If an imbalanceis noted, blower-door testing and IR thermography should be used.

Figure 12. Visual and infrared image of a new residential building with air-leakage.



Figure 13. Visual and infrared Figure 14. Visual and infraredimage of moisture and mold image of moisture in the

in the wall-papered outside sheetrock ceiling of a

wall of a hotel. private residence.

3.7 Commissioning and Maintaining Flat and Low-Sloped Roofs

After a new roof or recover is installed on a building, it should be commissioned by

infrared NDT. The roof is designed to keep water out and heat in. Roof waterproofing problems manifest themselves in two ways: leakage and entrained moisture contamination.

Leakage would appear to be simple, but the leak inside the building rarely directly relates tothe exact spot on the roof, since the water flows down the slope of the roof to a spot that isnot sealed and into the building at that point. Most leaks occur where the waterproofing is

sealed or where there is a penetration of the roof. Since most types of roof systems absorb

some amount of water, it is harder to find the exact spot of water in the insulation because itmay not leak into the building until it has absorbed all the water it can hold.



3.7.1 NDT of Flat and Low-Sloped Roofs

There are three types of NDT surveys that are used to find water in a roof: nuclear gauges,

which count neutrons; capacitance meters, which measure resistance; and infrared, which

measures heat. Both nuclear gauges and capacitance meters are used to take spot readings

on a 5’ x 5’, 10' x 10' or 20' x 20' grid on the roof. These measurements are used toextrapolate where the water is from the readings obtained from the gauges. These surveys

are very labor-intensive and therefore expensive. They are good for types of roofs that donot gain or lose much solar energy and therefore, do not lend themselves to infrared.

3.7.2 Roof Infrared Basics

During the day, the sun radiates energy onto the roof and into the roof substrate, and then atnight, the roof radiates the heat back into outer space. This is called radiational cooling.

Areas of the roof that are of a higher mass (wet) retain this heat longer than that of the

lower mass (dry) areas. Infrared imagers can detect this heat and "see" the warmer, highermass areas, during the "window" of uneven heat dissipation (see Figure 15).

Figure 15. Representation of daily radiational heating and cooling cycle.

3.7.3 On-Roof and Aerial Infrared NDT

Performing infrared roof moisture surveys while standing on the roof is not the best method

because imagery from a walk-on survey is not as useful as aerial imagery. But there are afew advantages to performing on-roof surveys. Small roofs are less expensive to survey.

Roofs can be marked with paint so that repairman can patch small areas (see Figure 16).

Figure 16. Visual and on-roof infrared image of a wet area on a flat roof.



The same laws of physics apply to both on-roof IR and aerial IR. A dry roof, low winds andno rain are needed on the night of the survey. A high angle of view and high resolution are

needed to produce usable imagery. Visual photographs are taken and used to make accurate

CAD drawings. By marking up the CAD drawings with the wet areas, surgical repairs are

made, commissioning the building and thereby extending the roof’s useful life.

Figure 17. Visual image overlaid with CAD drawing and infrared image showing

moisture laidened insulation in the roof substrate in a low-sloped roof.



Figure 18. Visual image (top) of a roof being recovered and an infrared image

(bottom) showing that the roof being covered is almost completely saturated.



Both visual and infrared images are used to do the analysis by overlaying the AutoCADdrawing of the roof ‘over’ the digitized photographs and thermographs. The drawings are

created indicating areas of suspected moisture contamination. The result is a report where

visual, infrared and AutoCAD components (printed and video) are well matched and lined-

up (see Figure 7).

3. Conclusions

There are many advantages to using infrared thermography in building applications:

• The building can be verified built to the specifications of the architect and engineer.

• If faults are discovered during IR testing, a high quality graphic report of the faults

can be generated so that repairs can be made in a timely manner.

• Confident that what he puts in the specifications will actually be built, there is littleneed for the engineers to ‘overdesign’ the building, to compensate for previously

undetectable faults that are ‘inevitable’. This saves the owner from having to pay for

more materials than are needed and simplifies the construction process, savingvaluable time and money on the job.

• Since the building can be documented and verified code-compliant, the ownerenjoys the confidence that the building will hold the weight of the roof and

withstand high winds.

• A detailed report and follow-up repairs will reduce the owner’s liability in the event

the building is visited with some trauma like a hurricane or tornado. After a disaster

has occurred, a forensic survey of the building are laid on the ground might revealsubstandard building components or practices and the owner could be held liable fordamage to property and/or loss of life.

• General contractors can reduce the costs of inspections, since many components and

systems can be checked without slowing down the building process.• Subcontractors who are not willing or capable of producing buildings without

multiple defects, eventually will not bid on projects where IR has been specified.

• When an retrofitting or adding on to an existing building, IR can identify tie-in

components, saving the designer from performing destructive tests and/or trustingthat the as-built drawings will contain accurate information.

Infrared NDT is a challenging field of infrared thermography. There are many different

types and uses of buildings, many different construction techniques, building materials andconfigurations. A building NDT infrared thermographer must be familiar with construction,

thermal dynamics and characteristics of any of the different building components. Design

flaws, structural defects, improperly installed insulation and moisture walls and roofs can be found and corrected.

Documents

Applications for Infrared Thermography as an NDT Method for Buildings by Greg Stockton Manuscript