Can One Area of Mold Growth Make an Entire Home Unsafe?

I realize that reading mold research and scientific studies about mold is not everyone’s “thing,” but unfortunately for my husband and close friends, it has sort of become mine. The many nuances of our built environments, how each component influences indoor air quality, and how indoor air quality then influences our health (good or bad) totally fascinates me. I truly cannot consume enough information on the subject these days. When a home or building with mold growth is making people sick, there is so much more going on than just the mold. Often, there are bacteria, yeasts, viruses, excess humidity, dust mites, ventilation issues, damaged and decaying building materials, and much, much more. In my opinion, examining how each of these factors influence and affect indoor air quality is at the crux of us figuring out how to prevent mold and environmental illness and how to actually make those that are already sick become well again. My belief is that if we fully understand what is causing the illness, then the cure will become clear, right?

Additionally, I love Building Science and IAQ studies, because they tend to be straightforward with findings that are conclusive—a refreshing change from the studies that deal with the myriad health issues associated with them. It is not that I don’t find value in the mold and health studies–quite the contrary. It is just that without established, definitive lab tests for mold and environmental illness, the human health studies still don’t seem to show us much more than the fact that, “Yes,” there IS a causal relationship between exposure to “sick” indoor environments with excess mold growth and a decline in health. We have essentially known that since Biblical times, but, still don’t seem to be progressing forward much. Thus, I believe studies about mold and how it behaves inside our homes and buildings are what we need to look to for the answers required to make us safer. If we can study and understand how and why certain contaminants are making our environments sick, we can address those things in a more proactive manner or remediate more effectively when things like mold are found and begin to make us sick.

Mold Spore Migration Inside a Home

A recent study published in Environmental Science and Technology Letters, entitled “Spatial Gradients of Fungal Abundance and Ecology throughout a Damp Building” (Bridget Hegarty, Ulla Haverinen-Shaughnessy, Richard J. Shaughnessy, Jordan Peccia) examines the question of whether or not mold growth from water damage in a basement can actually migrate to and contaminate the rest of a house. The topic of mold migration is an important one to look at, because many people feel dubious about the real health dangers of only a small, contained area of mold growth. For example, I get emails from homeowners wondering if they are being “had” by a prospective remediator who wants to treat their entire home for mold, even though the only visible mold growth is in a wet basement or crawlspace. In these cases, the homeowner can’t understand why the remediator needs to completely contain the moldy area, AND wants to also treat the rest of their home for mold spores. They don’t see any mold in the upstairs rooms or smell anything musty. Why is a whole-house clean necessary? Up until calling the remediator, the homeowner had often just closed the basement door and avoided going down there. In their minds, closing the door kept the mold separated and contained until they could hire someone to deal with it. All of this talk about cross-contamination and microscopic mold spores invading the breathing air in the rest of the home is just a ploy to make the remediators more money, right?

Other times, I hear from very ill people who have had their homes professionally remediated, but are still very sick and are still reacting inside their homes despite all of the work that was done. In these cases, often when I dig into the details, I realize that the remediation was not very thorough and/or containment of the mold was not done properly prior to or during the remediation. In either case, my response is always to caution the homeowners on the side of being thorough and safe with any remediation, because I know firsthand the health dangers of not doing things right from the get-go. What I always try to convey is that fact that many families are not made sick by the mold until walls are opened up and cleaning or demo occurs that liberates millions of microscopic mold spores into the air. Once that occurs, making a home safe again becomes much harder and much more delicate. But, I realize that warning of the invisible mold spores and of the mycotoxins that can be present is often a difficult case to make. That is where this study comes in. It actually tests, measures, and provides proof that mold spores CAN and DO migrate. In fact, they migrate quite a bit and do so without the assistance of foot traffic or mechanical ventilation systems and ductwork within an indoor environment.

My Simplified Overview of the Study

This study examines the question of how much mold growth from water damage can actually contaminate a home. It looks at how an identified, singular space of fungal growth influences the fungal ecology of the residence as a whole—as in, to what extent can the mold growth in my basement get into my child’s second floor bedroom? And, while the paper does not attempt to address the health implications of mold and whether or not the presence of mold in a home makes residents sick, it does examine the data from the assumption that human health could be influenced by persistent mold growth in one area of a building; because, as long as there is mold growth, there is potential for exposure.

The scientists who collaborated on this paper also examined the question of how the growth and abundance of water-damage molds or what we now know of as “health-adverse” molds influence the overall fungal ecology of a home. This piece, although not always discussed, is important, because our homes, like our bodies, have their own microbiomes. Our homes are full of bacteria, molds, dust, dirt, etc. from the humans and pets that live there, from the foods we eat and store inside of them, the outdoors, and the materials we have used to build and furnish our homes. Homes and buildings are not germ-free or sterile, nor should they be. In fact, our indoor environments have normal fungal ecologies that are diverse and thriving, but usually not harmful to our health. Some even say that a child who grows up in a home with a very diverse fungal ecology will be healthier and have a more robust immune system than one who grows up in a less diverse home. Asthma in children has actually been directly associated with exposure to indoor environments with less diverse fungal ecology and a dominance of water-damage-indicating molds. Thus, in examining how mold growth from water damage can influence overall fungal ecology in a home, we are getting closer to being able to answer the age-old question of whether or not “one bad apple spoils the barrel”—or in this case, whether or not certain types of mold (water-damage molds) can “spoil” the house. (In my opinion, answering this question will also highlight the need for DNA-based mold sampling in water-damaged homes to help determine the extent of remediation efforts).

The Details: Methods, Measurements, and Materials

Very basically, to conduct this study, the scientists located a single-family home in Southern Connecticut that had suffered a water incident in its below-grade basement. The water damage had occurred 12 months prior to the study. According to the study, the following conditions describe the indoor environment of the home:

“The basement was typically unoccupied and used for storage. It contained approximately .75 square meters of cumulative visible mold growth on sheetrock and wood trim. No other areas of the home contained damp materials or visible mold growth. The home was heated by radiators with no forced air HVAC system and was cooled by a split system air conditioner; thus, no direct mixing was occurring between the basement’s air and the first and second story. In addition, a door separated the basement from the first floor. For the most part, this door was kept closed, although over a typical day it was opened and closed “at least five times when items were being retrieved from the basement.”

For their experiment, the scientists collected settled dust from the tops of door and window frames to represent long-term airborne mold concentration in the home. They did this, because the dust on door frames and window frames is typically not disturbed by homeowners and provides a better snapshot of long-term exposure. (Note: This is similar to the dust that inspectors and homeowners are advised to collect for ERMI and HERSTMI-2 samples. You want the dust that has been undisturbed and in the home the longest. It will offer the best picture of the home’s mold history.) Settled dust samples were gathered to represent the outdoor air (for a picture of what is considered as “normal fungal ecology”) and indoor air from three different floors in the home: second floor (eight samples), first floor (eight samples), and basement (eight samples). Each indoor settled dust sample was taken from a different door or window frame in the home. Samples were also collected directly from the mold growth on the building materials in the basement (eight samples). All of the samples were collected using a swab-sampling technique on the same day. Characteristics for each sample were recorded at the time of sampling– room type, material sampled from, frame thickness, and distance to the direct mold source in the basement. This distance was measured as the distance the air would have to flow through the rooms of the house to reach the door or window frame that was swabbed.

The Study Results

Spoiler alert: The results show that “YES,” mold growth from water damage in one area of a home can and does migrate to the rest of the home, even when the contaminated area is not “lived in” and is closed off from the rest of the home. The scientists were also able to show that the overall fungal ecology of a home with mold growth from water-damage seems to decrease in diversity the closer to you get to the area of the active mold growth. Thus, not only is the health-adverse mold able to disperse all over a home, but a home with water damage seems to also have less fungal diversity as you get closer to the mold source.

Whew. Does that make sense? If not, I will break it down further:

• Mold from surfaces can impact indoor air’s fungal richness and community structure. This effect is strongest for samples taken closest to visible mold growth and weakens with distance.
• Mold from wet surfaces can distribute throughout other floors of a home, even without physical contact or mechanical systems mixing the air.
• The presence of direct mold in isolated locations in a home may result in exposure elsewhere in the building.

What does all this REALLY mean?

In short, this means that even if you are not going into the basement, or the musty crawlspace, or the attached garage with the wet and moldy wall, and breathing the “moldy” air, you can still be exposed to that mold in the other parts of your home. It also means that the closer to the mold growth that you get, the more concentrated the health-adverse mold spores are in your breathing air. And, finally, in my opinion, it also means that if you have any mold growth anywhere inside your home, it is the safest and best practice to BOTH set up strict containment before attempting any demo or cleaning of that mold, AND to thoroughly and consciously clean the rest of your home and belongings for mold spores as well to make sure that you are taking care of all possible avenues of mold migration or contamination.

How Important Is Overall Fungal Ecology to Indoor Air Quality?

Sometimes the more you learn, the more questions you have. Am I right? My biggest remaining question was about how the fungal ecology inside a home (the breakdown of what molds are present and at what concentrations) could influence the health of those living there—not because the study was aiming to answer that question, but because it confirmed that mold growing on surfaces DOES seem to have a direct influence on it. After all, it does make sense that, just like the gut microbiome, there is an ecological balancing act at play inside of our homes that is influenced (positively or negatively) by the overgrowth of molds, viruses, or bacteria. I don’t know why, but before reading this study, I hadn’t really thought about the importance of that balance in my own home.

We’ve always heard that to build a health immune system, we must come into contact with some bacteria and pathogens, but what about mold? Mold is everywhere and we are constantly exposed, but just like with bacteria, it seems like some mold exposures are just too much. Previously, my concerns about mold were mostly about overall exposure and keeping all indoor levels to a minimum. But, reading this study has me wondering how much of testing the DNA of the mold that is present really matters for the overall indoor air quality equation. It seems to be much more important than I thought.

One of the authors of the study, Dr. Jordan Peccia, PhD, Thomas E. Golden, Jr. Professor of Chemical & Environmental Engineering at Yale University, was kind enough to answer some of my questions. What follows is our exchange so that you may benefit too:

Me: Before your experiment, what did we know about fungal ecology in water-damaged or sick buildings? Does the “toxic” mold seem to dominate the overall ecology in these spaces?

Dr. Peccia: We knew quite a bit about the types of fungi that grow on damp building materials. However, fungi are extremely diverse. There are many species in a home . . . some there naturally, some there from growth on damp materials. The DNA approach we used ensures we catalog almost every species present, so we can better sort them out for making judgements of molding or not. Regarding the dominance of “toxic” species, the first thing is that we don’t always know if fungi is toxic, because this depends on the species, the metabolic state of the mold, and the sensitivities of the person exposed. In every home I’ve looked at (some of them very moldy), the mold that grows from water damage is always in the minority. That is, the mold that naturally occurs in a home (mostly coming from the outside) dominates the mold numbers in a home. However, an important point isn’t the relative percentages, it is the exposure.

Me: Can you simplify or summarize the kind of DNA sequencing that was done and why you included it in your experiment? I want to help the importance of this step to hit home with the readers. Was it just to show that the same molds in the basement that were caused by the water damage were also present in the upper living areas, or was it to show more?

Dr. Peccia: We take an air sample, extract the DNA, and then sequence it. We then compare these sequences to databases of known sequences, and this tells us the type (and numbers in some cases) of mold present. Using this approach, we get everything. This is in contrast to culturing or microscopy, where studies typically identify only a small fraction of the mold present. Under our method, we typically make hundreds to thousands of identification in an air or dust sample.

Me: As a result of this experiment, how important do you think DNA analysis is in testing homes that require remediation? Most air testing and bulk testing doesn’t dig this deeply, obviously, and many remediations fail–not necessarily because of the testing, but because most remediation companies only address the areas with the visible mold growth.

Dr. Peccia: It is critical. And, I believe it will eventually be the norm. In the near future, DNA-based mold testing will be available. They will be significantly more accurate than current approaches and can be done at a low cost as well.

Me: As a result of your findings with this study, do you have further studies planned to assess similar fungal migrations in homes with HVAC systems or with additional fungal distribution methods to see how those findings differ?

Dr. Peccia: The next study we will publish (Spring of 2020) will be on the development of a DNA-based diagnostic tool for assessing mold in homes and, hopefully, judging the success of clearance.

Have you read any helpful studies on mold inside buildings or homes that changed the way you remediated or currently practice “mold maintenance”? Did you find this post helpful? Have questions or comments? Write to me below or email me at catherine@moldfreeliving.com.