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Yes, There Is Mold in Your Home! When Does It Affect Value?

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As I stepped foot inside the home, the strong earthy smell was immediate. Walking through the home on the first floor I noticed that the ceiling fan blades were drooping down like wilted flower pedals. As I approached the basement door, I noticed that the walls of the stairway were speckled with thousands of dull black, green and dark gray spots that appeared to have a wave-like pattern going up the stairway walls from the basement. When I entered the basement, there was a dark growth on the walls and ceiling and standing water in the basement.

Mold In Hime

This describes many of the bank owned homes I appraised in the years surrounding 2008. Around that time, my appraisal business was slow. So, I took classes to become certified with the IICRC (Institute of Inspection Cleaning and Restoration Certification) to remediate mold. Shortly thereafter, my appraisal work picked up and I eventually let my IICRC certification expire. However, I have never regretted the education. I learned a lot about mold. So I thought I would talk about it.


Mold issues have become larger in recent times. In an attempt to build more efficient homes, newer homes are built more air-tight. That’s great for energy efficiency. However, it can be problematic at times. Why? Because mold is everywhere. Yes even in your house. A problem can arise when there is a high concentration of moisture on the interior. In certain situations, excess moisture in a confined area can set the stage for the growth of toxic mold.

What is a normal amount of mold spores? With mold remediation, the goal is to achieve a mold spore count on the inside that is equal to that of the outdoors. So yes, there is mold spores in every home. There are mold spores everywhere.

Toxic mold spores have a defense mechanism called mycotoxins.  These are poisonous, microscopic, spores that can break off of the mold with the slightest movement of air. Just walking past mold can create enough air flow to break these off. This is why you might see mold growing on stairway walls in a wave-like pattern. It’s because the mold spores are catching a ride on movement of air, as warm air rises up the stairway.  Once ingested, these mycotoxins can make even a healthy person sick. And for those with weak immune systems, the results can be even worse.

It should be noted that even if mold is no longer actively growing, the spores and their mycotoxins still exist and are just as poisonous. That is why killing the growth of the mold with chemicals is not enough. The spores must be removed.


Removing toxic mold is like herding microscopic cats. Herding cats of any size is difficult.

Before any mold is removed, the source of the moisture that created the environment for the mold to grow, needs to be corrected.

Next, any porous items in which toxic mold has settled must be destroyed. Things like carpeting, dry wall and most furniture made up of cloth materials. That in itself can be very costly.

Next, a negative air chamber needs to be created around the area that has been exposed to the toxic mold spores. The chamber is made of walls of plastic sheeting that surrounds the affected area. What is negative air? This simply means that instead of pushing air into a room, air is pulled out of a room. An air scrubber with HEPA (High-Efficiency Particulate Arresting) filters is used to accomplish this. The HEPA filters catch the poisonous spores. Negative air is used because it is a better way of controlling air flow and capturing the spores. If air was pushed into the chamber, mold spores would slip or be pushed through the cracks in the containment chamber more readily.

If a home uses forced air for heating or cooling, and if it was on while mold is in existence, then the ductwork and furnace will need to be cleaned. Also, if there is a possibility that mold has been spread to other parts of the home due to the forced air, than these areas have also likely been contaminated and will need to be cleaned as well.

Mold growth on hard surfaces, like wood, concrete, cinder block and other hard surfaces can be blasted off using a sand blaster or by blasting the surface with things like baking soda or dry ice. I found soda or dry ice blasting to be fun. Check out this video to see how.



Mold removal is very labor intensive, with a great deal of care being taken to use the proper PPE (Personal Protective Equipment) and following containment protocol. With mold remediation, a person must wear a plastic suit and respirator (mask) with the proper filters for mold. The filters must be designed for VOC (Volatile Organic Compounds).  Mold is considered to be a Microbial Volatile Organic Compound (mVOC).

If you are an appraiser, home inspector or agent, I recommend keeping a respirator, with the proper VOC filters, in your vehicle in the event that you have to enter a house with visible mold growth. These respirators are relatively inexpensive to buy.


If there is visible growth on walls and ceilings, chances are there is more growth behind the walls or trim. At times it is clear to see mold growth, but not always.

There are also times when there may be toxic levels of mold in a home that is not visible. So how can you find out? If you suspect that you have a mold problem, I recommend hiring a professional In-Door (aka. Industrial) Hygienist, or other qualified professional, to do the testing. Testing is very expensive, but proper testing will inform you, know not only how many spores are in your home, but also the type of mold spores you’re dealing with.

Spore traps and surface swabs are some of the ways that professionals use to test for mold. Throughout the process, tests have to be taken in both the affected areas as well as outdoors. Tests are taken before remediation begins and numerous times throughout the process until the levels are acceptable. Samples may cost $75 or more per swab or per trap. According to HomeAdvisor’s website, the national average cost for mold testing is $661. That is in line with what I have seen in the past. Even a relatively small area could end up costing many hundreds of dollars, just for the spore testing, not to mention the tedious work of removing the mold. There are tests that a home owner can purchase and use. They are less costly. However, they may not give you all of the information that you need to make an informed decision regarding the degree of remediation needed.

If you would like more information on how to test for mold levels, you might find the article, “How to Test for Mold in Air”, from ohsoSpotless. It has some good information. (Click here to read article)

This is why mold remediation, done the correct way, is so expensive. Just scrubbing the area with bleach water is not sufficient, contrary to popular belief! The costs of mold remediation alone, is one reason why mold issues can have a negative impact on market value.


Mildew is a type of mold. Mildew is generally not toxic. Mildew is sometimes referred to as Allergenic mold. It is generally white in appearance.  Some people are allergic to this type of mold. However, most people are not. Even if a person is, this type of mold is not typically life-threatening.

Toxic mold is a different more serious type of mold because it can release spores that are very toxic. There are several types of toxic mold that can cause more severe types of illness. They are far more dangerous than mildew and can cause permanent damage to those with weak immune systems. Black mold (Stachybotrys) is the most infamous molds. However, there are other toxic molds than can be just as poisonous. Some of them are Penicillium, Fusarium, Aspergillus and Cladosporium.  They all have a wide array of harmful qualities.


Will a mold growth on the exterior of a property, like the siding, have a negative impact on the market value or the marketability of a property? Probably not. Especially when it comes to being a health and safety issue. Remember, the goal of mold remediation is to have a spore count on the interior that is the same or less than what is on the exterior. So, if the mold is on the exterior, this is generally not a health concern. However, it may affect the appearance of the exterior of a home, which may lessen its market appeal. So mold on the exterior can have a negative impact in value for this reason. I once saw a home (not one I appraised), which had so much of a mold-like growth on it, that it appeared to have permanently discolored the aluminum siding. That would clearly have a negative affect on value.

When it comes to the interior, there are some things to consider. If you see some dark mold-like substance in some very small areas, say above a shower where there is regular moisture, that is not likely to have a major impact on market value. Nor would mildew in a bathroom. Of course, if this was the result of poor upkeep of the bathroom or other areas, there may be other factors that would impact market value, such as condition and appeal. However, a small amount of a mold-like growth or mildew is not likely to require major remediation.

However, if you see growth of a mold-like substance on walls, ceilings or floors in a home in areas that should be dry, this may be indicative of an area in which there may be mold growth. Anytime major mold remediation is necessary, there will be a negative impact on market value.  As already commented on, proper mold remediation is very expensive. So, this kind of situation is likely to have a large impact on market value.

Additionally, there is a stigma associated with toxic mold. So, the market in general is going to expect that any toxic mold be removed. The impact on market value could be very large, depending on the situation. I have appraised homes in which the mold was so extensive, that the cost to remediate the mold exceeded the market value of the home. Generally in these cases, the home is razed. The times where I have seen this were with bank-owned homes. Generally, if a home is occupied, the owner will recognize that there is a problem long before it gets to that point.


As already stated, it is always best to wear a proper respirator before entering into an area with mold growth. Because the cost to remove mold can vary greatly, it is advisable to have a professional remediation company, who is certified for mold remediation, provide a cost estimate. Keep in mind that the estimate could go up during the remediation process, depending on what is found behind walls, under floors and in attics.

When it comes to identifying mold, it is always better to not make an assumption that it is mold. Is it toxic mold or just mildew? If it is toxic mold, what kind or kinds is it? Even someone certified to remove mold, as I was, is not generally qualified to identify it. So, it’s best to not state that something is mold, even if we are pretty sure it is. In my appraisal reports, I refer to any such growth as being a “mold-like” growth or substance, unless already identified by a qualified professional.

So, the next time you open the door to a home you’ve never been in before, and you’re hit with a strong earthy smell, and you see evidence of excessive moisture on the interior, like drooping ceiling fan blades, don’t go into the home without a respirator!  Thanks for reading my blog!

Here is my monthly market update for January 2019. You can download the report or enjoy a visual version.  I hope you find the information useful. Northeast Ohio is having a strong start to 2019!  You can find more reports on my website at

January 2019 County Market Update



Here are some other articles and videos I enjoyed recently! I hope you will also…

The Apple Peeled – Ask the Experts: market Dynamics with Jonathan Miller – Matrix Blog by Jonathan Miller

Spocking Fives for Housing To Live Long and Prosper – Housing Notes by Jonathan Miller

What’s A Comp and Why Should You Care? – Yolo Solano Appraisal Blog

The players in the market & normal pendings – Sacramento Appraisal Blog

The Fallacy of Price Per Square Foot and a Highway 280 – Chelsea Real Estate Update – Birmingham Appraisal Blog

Interview with Craig Morley – Appraiser’s Minute with Tim Andersen

Kaizen – Continuous Improvement in Your Appraisal Business – The Real Value Podcast!

Lake Kiowa Market Update? – DW Slater Blog

Here Come the Zestimates – The Appraiser Coach Video Podcast

Clients Need To Know Reliability – George Dell’s Analog Blog

For my appraiser friends – Ann Arbor Appraisal Blog

Workfiles & USPAP Compliance – Appraiser eLearning


2 thoughts on “Yes, There Is Mold in Your Home! When Does It Affect Value?”

  1. You bring a really interest skill set to the profession Jamie. I enjoyed the post. I especially like how you said, “Removing toxic mold is like herding microscopic cats.” 🙂

    On a related issue, this is why there is concern over indoor cannabis grows at residential properties. Moisture damage is no joke. The plants need both lots of water and lots of heat, and that’s not always such a great result for the house….

    1. Thanks Ryan! It has come in handy a time or two.😁 Growing cannabis is an interesting point I had never thought of. A new day and a new set of things to think about. Working in real estate never gets old.

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