This homeowner knew she had mold. The question became, why was it there?
When this Central Austin homeowner called House of Thyme, she was already seeing mold in several parts of her recently remodeled home. She had spent a lot of money making the house nice, and now mold was showing up in and around cabinets in the kitchen, dining area, and other rooms in a variety of colors. Some of the cabinets had plumbing but others did not. She had no idea why her newly remodelled home was being overtaken by mold and had been bleaching the mold in vain.
This customer was specifically looking for someone with a building-envelope background and not just a basic mold inspection. She did not need someone to walk in, collect one air sample, and tell her there was mold. She could already see the mold. She wanted someone to look at the whole pier-and-beam house, including the crawlspace, attic, walls, HVAC system, and other places that could help explain where the moisture was coming from.
We approached the inspection as a whole-home investigation. We used visual inspection, moisture meter mapping, infrared thermal imaging, wall-cavity investigation, mold air sampling, and surface sampling. The goal is always to use each tool as one piece of the story instead of relying on a single mold test to explain the entire house.
One of the first things that stood out was the indoor humidity. The relative humidity in the home averaged around 65% during the inspection. That is high enough to matter because mold does not always need a dramatic plumbing leak to grow. When the air inside a home stays humid, materials such as drywall, wood, cabinets, clothing, and dust can stay damp enough to support growth. The homeowner was also seeing mold on clothing and belongings, which told us this was not limited to one wet cabinet or one small plumbing problem.
The kitchen gave us an even bigger clue. We found elevated readings behind the stove wall and investigated the wall cavity. There was visible fungal growth inside the wall, but there was no sink, refrigerator water line, or other obvious plumbing source in that location. That matters because when mold is growing inside a wall with no clear pipe leak, we have to start looking at other moisture sources, such as rainwater getting through the exterior wall, condensation, air leakage, high humidity, or another hidden building problem.
The laboratory results confirmed that the kitchen wall was not dealing with a normal background level of mold. The outdoor control had 400 Aspergillus/Penicillium-type spores per cubic meter. The kitchen stove wall cavity measured about 369,000 spores per cubic meter, or more than 900 times the outdoor level. That large difference supported what we were already seeing inside the wall and was consistent with an active indoor mold source rather than normal outdoor spores entering the home.
Unfortunately, the kitchen was not the highest result we found. A second wall cavity between the office and ensuite measured about 1,110,000 Aspergillus/Penicillium-type spores per cubic meter. That was more than 2,700 times the outdoor level. Because this wall was close to the tub and shower, the location also raised concern about possible long-term moisture exposure in that area.
We also collected an ambient air sample in the primary bedroom. The overall mold count there was lower than the outdoor total because Austin outdoor air naturally contained many seasonal spores that day. But the type of mold mattered. Aspergillus/Penicillium-type spores in the bedroom measured about 12,100 spores per cubic meter compared with only 400 outdoors, roughly 30 times the outdoor level for that mold group. That gave us another clue that material from the hidden indoor sources could be making its way into the living space.
The mold test results were important, but they were not the whole investigation. We were also finding moisture clues in other areas of the home. Moisture readings were elevated below a living-room window. The backside of the kitchen stove wall showed elevated readings. The wall near the primary shower showed signs of moisture, and bubbling paint near a low electrical receptacle suggested moisture could be trapped behind the painted surface.
Infrared imaging also showed temperature differences at some of these same areas. Infrared cameras do not prove that a wall is wet, but cooler areas can be a clue because evaporation from damp material can lower the surface temperature. We use thermal imaging to tell us where to look more closely, and then we compare those findings with moisture readings, visual conditions, the history of the house, and testing.
The attic and exterior construction gave us more questions about how the house was managing water and air. The water-resistive barrier, or WRB, appeared to be installed on the inside face of the exterior structural sheathing rather than in the typical location outside the sheathing. That did not by itself prove it was the cause of the mold, but it was important enough that we recommended opening sections of the exterior around windows to see how the wall assembly and water-resistive barrier were actually tied together.
We also found a damaged gutter and fascia area, and the primary bathroom exhaust fan was not properly connected and sealed to its dedicated roof exhaust. Each of these findings mattered because this house was showing us more than one possible way moisture could be getting into, or staying inside, the building.
This is where it would have been easy to oversimplify the inspection. We could have found one unusual construction detail and called it the cause. We could have found mold behind the kitchen wall and stopped there. We could have blamed everything on the high humidity. But homes rarely work that neatly, especially older Central Austin homes that have been remodeled over time.
Instead, we looked at the findings together. The home had elevated indoor humidity, very high mold levels inside hidden wall cavities, moisture around windows and the shower area, questions about the exterior wall assembly, a bathroom exhaust issue, and questions about how the newer HVAC system was controlling humidity and pressure inside the home. The evidence showed that the mold problem was widespread, but finding the mold was only the first part of understanding why it was happening.
The next step was professional mold remediation, but we did not want the plan to stop at removing contaminated materials. The recommendations also included having the HVAC system evaluated for sizing, distribution, air leakage, and moisture control; opening sections around exterior windows to better understand the wall assembly; repairing the damaged gutter; investigating the tub and shower wall; and lowering indoor humidity.
The remediation protocol also went further than simply telling a contractor which drywall to remove. Because the investigation raised concerns about air leakage between the house, attic, crawlspace, and exterior, the protocol included recommendations aimed at reducing humid outdoor air moving into the house and helping prevent the same conditions from returning after remediation.
This is also why cleaning visible mold with bleach was never going to solve this house. The mold on the cabinets was the part the homeowner could see, but some of the strongest mold findings were hidden inside the walls. If the moisture source, humidity, air leakage, or building-envelope problem remains, cleaning the surface does not change the conditions that allowed the mold to grow.
For this homeowner, the important answer was not simply that mold was present. She already knew something was wrong. What she needed was an investigation into why mold was appearing in different parts of her Central Austin home, including areas with no obvious plumbing leak.
That is the approach we take at House of Thyme. Our mold inspections in Austin are rooted in building science because mold is usually the result of a moisture problem somewhere in the building. Sometimes the answer is a plumbing leak. Sometimes it is a window, shower, HVAC problem, high indoor humidity, air leakage, or a building-envelope issue. Sometimes several things are happening at once.
If you are finding mold in different parts of your Austin home, especially if it appears in areas with no obvious water source, the next step should be more than simply asking, “Is this mold?” A whole-home mold and moisture investigation can help answer the more useful question: Why is it growing here, and what needs to change so it does not keep coming back?
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Texas Department of Licensing and Regulation (TDLR)
Mold Assessment Consultant: #MAC2207 Exp 11/27
TDLR Consumer Mold Information Sheet
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