By Stephen Andrews

Some people seem to have an uncanny sense of smell for mold spores. After receiving a call from one such customer, I was asked to perform a thorough mold investigation, utilizing all the resources at my disposal. Upon arrival, I prepared for my inspection of the eight thousand square-foot, two-story house, wondering how I would ever locate the needle in this particular haystack.

The home was almost brand new, and had been built by one of the nation’s largest builders – a reputable firm. But shortly after moving in, the homeowner began to notice a moldy smell when she opened the door to the basement. The builder hired three different inspectors to perform mold investigations (including mold tests), but no one was able to find the source of the odor. What frustrated the homeowners the most was that no other person could smell the odor. While the builder had tried to do the right thing by engaging professionals to find the problem, in the end he concluded that the problem was in the customer’s head. To his credit, however, he did offer to pay for the owner’s investigation—if someone could actually find the problem.

Although the house was less than a year old, the owners were concerned their warranty was going to expire before the source of the odor was found. In addition to the smell, the Mrs. seemed to be sensitive to mold exposure—every time she would go into the basement it would make her sick.

I began my investigation by measuring moisture levels in the concrete foundation walls and floor. I took air samples and carpet samples for lab tests. The moisture in the concrete walls was 18% and the floor slab ranged from 24% to an unbelievably high level of 74%. The air test came back within normal levels but the carpet test indicated unusual levels of mold spores. I suspected the high levels resulted from active mold occurring within the basement over a period of months with mold spores accumulating in the carpet.

Although other inspectors were unable to identify any visual mold growth, I found a light dusting under the enclosed stairwell. It was difficult to find, but if the inspectors were patient and knew what they were looking for, they could have seen the mold on the bottom side of the stair treads and kick boards under the stairwell. For the better part of a year, the stairwell had been trapping moisture rising from the concrete slab, which created occasional conditions for mold growth. It was a step in the right direction; however, this alone did not explain the problems my customers claimed they were having.

I looked around once more for clues. It seemed that every square inch of this house had already been tested. Then I noticed the landing at the base of the stairwell. It was completely encased—trapping moisture from underneath the landing. Because the moisture levels were so high in the concrete slab, I was sure we would find mold growing inside the stair landing. I recommended cutting an inspection hole. Sure enough, heavy visible mold growth had occurred in just over ten months. It turned out that the active mold growth under the stair landing was the primary source of both the odor and the mycotoxins that were affecting the homeowner. After remediation, my client was satisfied the smell was gone, and even felt safe going into the basement again with out fear of mold exposure.

After every remediation project, I sit down with the client and make recommendations for mold prevention. No one wants to go through the expense of mold remediation twice. For this particular house, I recommended installing a dehumidifier, ventilating the stairwell and stair landing, and installing louvered doors on closets and cabinets in the basement to control the moisture.

Without proactive steps, there would be a great potential for future mold growth in this home. The unusually high moisture levels in the concrete slab present ongoing challenges. The owners must be careful to make sure the slab moisture does not migrate to other areas or materials, creating conditions for mold to grow. But armed with the right tools, good ventilation and a better understanding of how to control their environment, the homeowners can enjoy their home for years to come.