Thermal image example, Paul Probett, Incodo 2008 Thermal Imaging for Mold Detection
Consumer warnings about severe errors when relying on thermal scans for building mold detection

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IR or Thermal Scanning for Hidden Mold: case study evaluates the ability of thermal imaging to find hidden mold contamination in a New York Home.

As we discuss in detail at THERMAL IMAGING, THERMOGRAPHY, thermal images and IR have been widely used with some success at spotting areas of heat loss in buildings and these tools have a longer history of use in examining overheated electrical connections, motors, etc. But thermography for finding hidden mold reservoirs is a hit-or-miss proposition, as this article illustrates. Page top image of thermal scan results provided courtesy of Paul Probett, Incodo Ltd., a New Zealand Forensic Building Specialist.[1]

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Does Thermal Imaging Find Mold Contamination in Buildings? Case Study Report

Toxic Black Mold IR Scanner - like the light meter replacement window scam

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 The most egregious instrument snafu I've come across [DF] recently was a Hudson Valley New York "mold remediator" uses an IR camera to tell himself and his clients where hidden mold is located in their home.

The homeowner complained of high sensitivity and allergies to mold and told me that her bedroom was the place where she was most irritated - she suspected a mold problem nearby, had hired the thermographic camera-equipped mold contractor, had him treat her home, but felt no reduction in her indoor air quality mold-suspect complaints.

After this high tech pay and spray "mold remediation job" produced no relief, I was asked to examine the building further. I cut test openings into walls where he'd been spraying his sanitizer - there was no mold in those cavities to start with. By inspecting the building outdoors and inside, and by listening to the client, and perhaps by luck too, I was able to find a mold problem whose removal also abated the occupant complaints in the home.

We Checked the Area of Prior Mold Spray Treatment

At below left our photo shows one of the plugged openings where the contractor had sprayed his sanitizer - along a dining-room window where (no surprise on a 1960's ranch house) his thermal camera had shown temperatures a bit lower than other wall sections. The treatment areas was a bit far from the problem bedroom. With owner permission we decided to take a look into the treated wall cavity. At below right you can see the wall cavity side of our test plug cut - indeed we found a stain explained below, but no mold whatsoever on either side of the drywall surfaces - not by eye and not by lab test.

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007

At below left you can see the building wall cavity insulation vapor barrier (black kraft paper) and insulation (green fiberglass) where we removed a new test plug to make an exploratory wall cut in the area the contractor had asserted was heavy mold growth. At below right you can see the wall sheathing, framing, and cavity details. By visual inspection, surface test samples, and vacuum samples we found no evidence that there had ever been mold contamination in this cavity. We also saw by liquid marks that what we thought may have been water marks from leaks were traced to the application of sanitizer. .

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007

This approach to finding hidden building mold was as unreliable and nonsensical as the window replacement company salesmen who used to use a camera light meter (which pegged its needle whenever exposed to brighter light at any building window) to identify "leaky windows".

So If There Was a Mold Problem, Where Was It? Start at the Building Exterior

I did find areas of basement water entry and moldy insulation. (FIBERGLASS INSULATION MOLD - in an area never examined by the thermograph er. Starting outdoors we identified all of the likely leak points on the home, roof to basement, with special attention to the exterior walls and attic surrounding the problem bedroom. Our photos below illustrate our discovery of a long history of leaks into a cantilevered floor cavity that was under the plaintiff's bed. Notice that deep drip line in the soil? That led us to lie down, squirm under the floor overhang and look up. At below right you can see what we found. Leak stains.

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007

Continue By Inspecting the Building Interior

Below are photographs from the home's basement, looking at and then into the cantilevered floor section. We found leak stains and some visible mold on wood surfaces as well as on some of the insulation in that area.

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007

Confirmation of the Mold Reservoir Theory by Lab Tests & Photographs

In our forensic lab we confirmed the presence of Pen/Asp spore chains in air and dust in the bedroom, and long Pen/Asp spore chains and mold growth actually inside the fiberglass insulation that had been below the bedroom floor. Why would mold "grow" in relatively clean fiberglass insulation?

Certainly if the building insulation has remained clean and dry the mold risk is very low. But where the material has been wet, occupied by insects or rodents or other sources of organic debris, and possibly where the resin binder is mold-friendly, we sometimes find rather high Aspergillus sp. and on occasion Penicillium sp. therein (photo below left).

Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007 Thermographic mold scan investigation (C) Daniel Friedman for JZ 2007

Pen/Asp spores in spore chains (red arrows in photo above) confirmed active or recent nearby fungal growth, not just a volunteer spore or two that came in to the insulating material from the air. At below right our photo illustrates other fungal growth and mite fecals collected from the wood surfaces in the same building floor cavity. More detail about the occurrence of mold in fiberglass insulation is at INSULATION MOLD CONTAMINATION TEST.

New Zealander's Photographs Demonstrate How IR Thermal Imaging Miss Hidden Mold

Thermal image example, Paul Probett, Incodo 2008

Mr. Probett's slide shown at left illustrates a point that we also emphasize: neither a moisture meter nor an infra red / thermal scanning device will report an area of prior water leakage or hidden mold if that area has dried at the time of the building survey.

And simply pointing to temperature differences in a building does not assure that we are pointing out moisture leaks and certainly not mold.

The upper photos show what looks like a clean building interior (far left) that actually harbored a significant level of mold on the wall surface behind wallpaper.

The lower photos illustrate that the thermal image reports no significant temperature inconsistency that would have pointed to this mold contamination.

Paul Probett adds: We had major problems with people buying thermal imagers, using ex military units and making ridiculous claims. In 2008 I gave a power-point presentation [25] [adapted in this article] to a conference explaining how IR results can be fudged and I described the limitations of thermal imagers.  (Our staff had been through the Infraspection Institute USA on-line course to level 2 the year before).

An adaptation & expanded version of Mr. Probett's 2008 thermography presentation are included in the text and illustrations at THERMAL IMAGING, THERMOGRAPHY.

Many Effective Untruths Contain an Element of Truth

Photograph of mold found behind paneling in a bathroom.Like practices of questionable honesty, there was an element of truth to the mold remediator's IR pitch: if indeed there had been a recent water leak into a building cavity, the IR scanner might be expected to pick up a temperature difference at that location. And since a water leak into a wall can cause mold, there might be a mold risk. But

In fact there was a problem mold reservoir in the building discussed above, but it was nowhere near any of the locations treated by the contractor - it was not even on the same building floor level..

The Contractor Treated the "Not Mold" Areas and Completely Missed the Actual Mold Reservoir

In fact, the "remediation" procedure sold by the contractor was improper as well as ineffective. His use of thermal imaging, included "free" in his building survey for hidden mold, led to a dual error:

  1. The contractor sprayed for hidden toxic black mold where mold was not actually present in the building - also see MOLD SPRAYS, SEALANTS, PAINTS
  2. The contractor failed to find mold and remove it where problematic mold was in fact present in the building

Consumer Tips For Hiring a Building Surveyor or Mold Inspector

The person who screens your building for mold contamination or other possibly costly repairs and who defines the initial scope of work to be performed should have no business nor any other relationship with the contractor who will ultimately perform the work.

Reliance on "tests" for hidden mold without an expert visual inspection will not give the most reliable results and some building mold screening test methods are simply invalid.

Watch out: in the hands of the inadequately-trained or unscrupulous operators, many inspection & testing tools or equipment can wreak havoc or harm to consumers. At THERMAL IMAGING, THERMOGRAPHY Paul Probett discusses the ingredients necessary for successful use of thermographic or IR temperature scanning cameras & equipment and he also identifies sources of thermography errors.

Reader Experience with Infra-Red Mold Scan Nonsense

Home Inspector Touts Infrared Camera as Mold Detector

Thanks for your great website which offers great information. I am writing as I believe there aren't many people (professionals) who truly know about mold problems, how to find it, and the solutions.

I smell mold strongly in the kitchen area.of a single family bungalow. I can smell it when I walk into the house but it is definitely in the kitchen. There are 2 ceiling light fixtures at the ceiling, and I smell it when I stand under the lights, and I also smell it on the wall, at the plate covers the wall for electrical outlets. (seems that where there are openings in the wall and ceiling, I smell it there. (even where a wall hanging is mounted)

There is also a large window on one of the 2 walls in questions (the walls come together like an "L" and the window has a a double pane glass and the inside pane has a 10 inch crack. I smell it there too.

I had a home inspector who said he finds mold, came to do the mold inspection, and he brought an infrared camera and an air quality tester thing. He said his camera would show mold if it was behind walls or ceilings.. He said he didn't see anything.

He also told me that mold doesn't smell, and he said he doesn't smell anything. He did an "air quality test, by taking one sample outside, one in the inside entrance of the house, and then taking one in the kitchen, and all 3 samples came back negative for mold. (the inspection was done when it was -38 C outside, not sure if that is a factor.)

He held up this vacuum thing for a few minutes in each 3 location.

He also got on a ladder, and peered up into the attic crawlspace but not did go into the attic and cross any of the rafters. The kitchen is at the exact opposite of the house where the smell is located.The attic has an opening in the ceiling where he held a flashlight and and glanced around the 1100 square foot area.

Allegedly there was a gutter back up a year ago and I do not know how much water came in or where the water went in, but the 2 walls in the kitchen are the outer walls of the house that join where the backup allegedly happened.

The spouse doesn't smell anything, and is happy to believe the home inspector,and stop looking.

I am writing as I am planning to look further, but want to know if you can give me an idea as to where to start and what method (scope vs cut outs and where to make the first cut)
There are no visible stains, bubbling, or marks on the wall, ceiling or floor and the walls and ceiling was painted about 6 months ago. The floor isn't that new and I don't really smell it coming from the floor. The kitchen tap is also located on one of the walls in question, where under the sink appears to be dry and I don't get the profuse smell under the sink in that cupboard. There are also fridge lines that supply water to the ice maker across from the tap on the opposite side of the kitchen, possibly in the ceiling as well there is a vent above the stove at the other wall.

Out of 5 rooms on the main floor, the kitchen is the only room that I smell it in.

There were 2 general contractors who came before the "expert" house inspector" and the contractors walked in and said right away that they can smell it and identified the kitchen area without previously knowing that was as where I smell it.

Would you trust 3 negative air quality samples if you can smell it as well as an infrared camera?
(he did show me how placing my hand on the wall for a second, would soon show a glowing hand print by pointing his camera on it.)

Would you start looking deeper or leave it? Will it eventually become visible somewhere?

If you were going to look further where would you make your first opening and with what tool?
Would you go on the rafters in the attic first?
Is there anything that can be done less invasively from easily lifting the siding at the outside of the house?

Thanks for your time (there will be a newborn with lung issues coming and I want to ensure there is no hazard.... )
I do trust my nose, and it is definitely the smell of rotten mold. If I could describe it, better, I would say moldy wet wood smell. I can also smell it a bit outside in the yard at the same wall with the earlier gutter backup.. which was fixed allegedly at the time of the back up.


Bob, if you smell mold there is probably mold nearby. Most people's smell sense is pretty accurate in this area. Find and follow the building leak history and to be thorough, also examine the structure, its design, ventilation and materials to notice areas of possible moisture traps even where there has not been an actual leak, and to spot mold-friendly materials in those wet or damp areas. .

Regarding the description of the rather questionable mold "inspection" by a home inspector in which you stated:

"..he said mold doesn't smell"

Nonsense! While it is true that not all molds create smelly mold-volatile-organic compounds or MVOCs, many do. If you smell mold, there is or has been mold contamination nearby. A few other chemical odors might be mistaken for mold but not many - most people are pretty accurate at identifying "mold smells" if they are present.

Absence of mold smell is not proof of absence of mold contamination. But presence of mold smell is good evidence of mold contamination.

Tell your home inspector to wise up or give you your money back.

About your comment that you

" ... had a home inspector who said he finds mold, came to do the mold inspection, and he brought an infrared camera and an air quality tester thing. He said his camera would show mold if it was behind walls or ceilings."

Baloney again!

Infrared scanning can spot temperature differences, not mold.

IF a building is wet due to leaks the IR scan might find the wet area; water is a gating condition for mold so such a finding might point out a place to look for wet conditions and mold in a building cavity.
But a leak or moisture trapped in building cavities could have inoculated a serious hidden mold contamination problem long ago in an area now dry. The IR scan won't find a darn thing but there could be a significant mold contamination problem.

Details about this confusion between making money using IR scanning and valid mold investigation methods can be read further in the article above.


Thanks for your reply. I'm just wondering where and how a person would start? What would make more sense? Would crawling up in the attic rafters be the first place, (so to look in the area of the smelling room beneath, which is farthest away from the attic opening) or would taking out a piece of drywall in that smelling rom, be first choice?

Its so invasive...If taking out a piece of drywall is first, would I go for the ceiling or the wall? Can it be done by the outside of the house with removing some siding? The walls that I smell it in, are both outside walls, with the smell also coming in from the ceiling attached to these 2 outside walls. Thanks again for your time...
In your reply you said.


At InspectApedia if you search for "find hidden mold" you'll see a number of suggestions; the basic approach is what I intended to describe: we ID the highest risk points first by studying the building leak and moisture trap history - examining in those locations.

Of course a competent mold contamination inspection inspects the accessible building areas before cutting anything open. The fact that you even ask this question tells me that your home inspector's inspection was not a useful one. A competent mold inspection begins outside, examining the entire structure, continues inside examining all accessible indoor areas, and includes a taking of the building leak history and occupant complaint history.

The combination of building design, structure, materials, and leak or moisture history, aided by occupant observations and complaints, tells us the most-likely areas where there may be a hidden mold reservoir needing attention. That's where we continue the investigation making test cuts as necessary. On occasion we also use a bore scope but I don't rely on that instrument alone any more than one can rely on a "negative-result mold-in-air test" to screen a building for hidden mold problems.

If it is easier to pull siding to investigate a high risk area than to cut and patch drywall, sure, that's an option. But I would not damage siding to save drywall. Drywall cuts are invasive only in that there may be a need for cosmetic repair and possibly re-painting a wall area or even an entire wall. Often we can explore high risk wall areas at the wall bottom by pulling off baseboard trim and making our opening there, avoiding visible wall cuts.

But in truth if we start by investigating the highest risk areas first, the cost of a later drywall repair pales compared with the cost of removing moldy drywall, removing moldy or previously wet insulation, cleaning a wall cavity, then restoring the wall.

See the hidden mold links given just below.

Reader Follow-up:

In my quest to get to the bottom of the problem, I have found that the equipment that the inspector brings in (infrared camera) is also very crucial. I am reading that the camera often used only picks up temperature differences of 5 degrees and more. I am reading that the difference where mold could be growing with moisture can show as little as a 0.7 degree difference.
I have also found that the resolution specs need to be as much as 260 x 360 as opposed to many mold inspectors cameras that will only have the capacity resolution of 16 x 36.

I have also found that your information regarding air quality tests was very helpful, as had I not come across it, I would have believed (I did believe) that a negative air quality test, is the proof in the pudding to put to rest the worry of having "toxic air".

I am thoroughly disappointed that "mold consultants" are not governed and apparently any "home inspector"( who has a "home inspector" licence, and has written a one page test on mold, can call himself an expert consultant with no liability. (or expertise)
It is misleading at the very least, where these people can charge an enormous amount of money only to tell the home owner, that his house is clear of mold, and his air is negative for toxins, and that there is no problem.

I realize the first flag should have been where he said mold doesn't smell, but when a person is needing professional help, who wouldn't trust the person who can call himself, an expert/consultant?

On account that there was a "smell concern" contained in a room where the exact point of the smell was pointed out, I now realize that his credentials were suspect, as he could have easily offered to remove a baseboard and/or an electrical outlet in the wall where he could have taken a peek or at least tried to get a smell.

When I called him later on, to find out about his qualifications I asked him if he was certified and he said he was and told me the names of where the certification came from. One was the home inspector association, the other was an online course for home inspectors where they learn about taking an air quality test, (that is free) and then once they pass it, they can call themselves experts.

Of course a person couldn't go after the "expert' once mold is found as you agree that he isn't responsible for anything that could have been missed, as well they could always say it wasn't there when they did their inspection.

I don't believe he took an tape samples of any areas, and even if he did I question how reliable they would have been.

Your site, gave me the basic knowledge where I learned that inspections are far more complex than one would imagine. Thanks for posting it. The invasive search for mold will take place next week, and I will update on the find. The smell is strong so one would have to think that its behind the walls somewhere.

If there is mold between the siding and the exterior sheathing, could the mold move in front of the vapour barrier closest to the interior drywall? Could it be on both sides of the barrier? Should a person start from the outside by removing a piece of siding and cutting out a piece of the sheathing, or should a person start from the inside, out?
(it has warmed up but still for spring, it will only be about 32F for the next 4-6 weeks.)

Reply: Clearing up the Foggy Claims around IR, InfraRed or Thermography Scans for Mold

Let's me try to be more clear about IR and air testing in hope it helps guide some other

The temperature differences and mold growth ranges you cite are inaccurate and not useful for two reasons.

1. of the 1.5 million mold genera/species, there are molds that will grow in a huge range of conditions - making narrow temperature specifications something less than helpful when screening a building for mold

2. FALSE NEGATIVE ERRORS: IR or thermal scanning or thermography will ONLY pick up temperature differences not mold. It will not, for example, detect mold growth in a building wall or ceiling cavity if at the time of the scan that cavity is not wet or drafty or cold for some other reason. As a practical example, many times we've found very extensive mold contamination in building cavities that showed no temperature variation whatsoever.

3. FALSE POSITIVE ERRORS: IR and thermal scanning also give a very high percentage of indications of "mold presence" where there is no mold whatsoever, just a temperature difference. For example I inspected and made test cuts into walls of a home where the owner complained of a mold smell. She had paid a "mold expert" to find and treat the mold contamination. The expert used thermal scanning, found cold areas around the window frames of the 1960's-built raised ranch in New York state, inserted a wand and sprayed biocide into the building cavities. Several thousand dollars of fee were completely wasted. We found on inspection that the areas treated were not and had never been mold-contaminated whatsoever. Rather the mold contamination was found in a different building area, one that was missed by the IR.

This approach to "mold testing" is as misleading as the old light meter trick: the replacement window industry salesmen used to walk through a home using a light meter, telling prospective clients that the meter was an energy-loss detector. When the light meter came near a window, needless to say the needle pegged.

Summing up the risks of relying on an air test for mold to screen buildings

The "air test for mold" approach is another example of a profitable service that can be of low actual diagnostic value. It is quick and easy, and when conducted without an actual inspection, a mistake: grab a sample, send it to a lab, the lab sends a report to the client. The field tester denies any responsibility, saying the lab did the technical work. The lab denies any responsibility, correctly saying that they only know what was in the sample, not how the sample was collected or whether or not it represents actual building conditions. A negative result - no mold detected- is not quite reliable; I find several orders of magnitude in the level of airborne particles just by waving a notebook in the air or moving the air sampler to a higher or lower level in the room.

A "positive" result (high problem mold counts) is indeed strongly suggestive of an indoor mold problem, but even then we don't have any diagnostic information and need to pay someone all over again to do the proper job: find the mold contamination reservoir and specify the cleanup needed.

What about mold trapped between building siding and wall sheathing?

If there is mold between the siding and the exterior sheathing, could the mold move in front of the vapour barrier closest to the interior drywall? Could it be on both sides of the barrier? Should a person start from the outside by removing a piece of siding and cutting out a piece of the sheathing, or should a person start from the inside, out?

Mold particles from some species such as Aspergillus are so small that they can move like a gas through buildings, following very small air leak passages. And MVOCs are gases and can move accordingly.

But mold between siding inner surface and the outer surface of exterior sheathing would not be a highly likely source of indoor mold spore contamination except in the most egregious case. (It might be a source of MVOC odors indoors).

Much more likely mold reservoirs indoors are wet or previously wet cavity side of drywall, wood framing, wood sheathing, and in some cases previously or currently wet insulation, particularly fiberglass. (Cellulose insulation, though made of paper, has been treated with a fire retardant making it much less mold-friendly).

These points are why following the leak path or accumulation area of water and moisture are important in finding a mold reservoir in buildings. But we do NOT want to send a maniac running through the building with an axe, chopping holes willy nilly. That's why we start modestly, with minimum invasiveness, small test cuts in most-suspect areas.

IF following that more gentle approach we can't find the mold problem but if other building evidence (odors, tests, complaints) make us believe that there is a good chance that a problem reservoir exists, THEN we might have to make what you called "flood cuts" and I call "strip cuts" removing 6-12" of drywall along entire lengths of a building wall or ceiling to look for the problem.

Using strip cuts we found that in a building whose lower floors had been flooded by the extinguishment of a fire on an upper floor the water had run across a ceiling and down inside of a wall cavity into a basement; but in the ceiling and wall cavities, as drywall and sheathing were tightly nailed to studs, water ran in just two joist bays and just three wall stud bays - which is why finding the problem with small test cuts had been unsuccessful. The strip cut showed the problem immediately. (IR or Thermography was useless as the building was already dry at the time of investigation).

Remarks on mold inspector qualification & certifications

While I am very critical of "mold inspectors" who took a weekend course or sent away for a mail-order diploma (easily obtained) certifying themselves with what is principally a marketing tool rather than true expertise, making clear that such folks often are simply chasing the enviro-scare mold dollar, I want to emphasize that a home inspector who takes a more thoughtful approach to mold investigation could be the most useful inspector one could hire to look for hidden mold problems in building.

How might this be? An experienced home inspector, a real one who actually inspects the building, knows better than many others (including industrial hygienists, engineers, and a laundry-truck driver who became a mold inspector to earn a better living) where leaks occur in buildings and where water goes. Because leaks and moisture are key gating factors in mold contamination in buildings, this expertise is immensely useful.

But an inspector of any stripe and with any credential who simply dashes into a building and grabs a test sample or two to send over to a lab, is not providing the most helpful service: even if such a test indicates that there is a mold problem in the building, the test is not telling us where it is, why it's there, and what cleanup is needed. If that's all your inspector did, I'd ask for a refund.

So how do we find an expert?

I agree that it's difficult for a consumer who is not an expert herself to figure out who the real experts are in any field. Just asking about credentials is not so helpful. We don't know if the cited credentials are valid, real, or just mail-order. Even state licensing is limited in usefulness in that at least in the states with whom I worked on licensing and testing were inclined to set the qualifications-bar very low so as not to exclude people who wanted to work in the field. One state education department head told me "We certainly don't intend to stand in the way of someone's ability to earn a living." What about protecting the public?

Ask about the inspector's experience. Listen to hear if the inspector regularly attends professional education courses, seminars, or the like. And best, just ask a question, any question, that invites the inspector to answer with some technical detail. If the inspector says "Don't worry about that, honey, we'll take care of it" then there are two reasons not to hire that person. First, he called you "honey" and second, there was not a shred of content in the reply. No content during the service-sales honeymoon pretty much promises no-content during the marriage.


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