Mold, or fungal growth, is a prevalent and contentious issue in Forensic Engineering inspections so we will dedicate some time to clarifying the issue. Fungi are essentially microscopic plants that reproduce by airborne spores, just like tree pollen. These spores are near ever-present in the air. If you leave a banana peel on the counter for a week or two, you will probably see primary colonizing mold colonies sprout up. This occurs as a result of airborne spores landing and germinating on the banana peel, which provides a nutrient-rich substrate.
Fungal growth requires the presence of spores, water, Oxygen, and nutrients within a narrow pH range to initiate and proliferate. Nutrients are commonly absorbed by breaking down plant fibers called cellulose. Cellulose is found all manufactured wood products; lumber, particle board, paper, etc. Common drywall has a paper face and backing, imagine a gypsum and paper sandwich. During construction or remodeling, we may reduce the available food for potential fungal colonization by choosing cellulose-free building products. Metal framing can be substituted for wood. Dens Armor Plus by Georgia Pacific is a great paperless drywall, and it costs about $1 more per sheet, money well spent. As a builder, I have incorporated it extensively in bathrooms, kitchens, plumbing chases, and exterior walls where high moisture levels are common.
Fungal growth in AC plenum
Mold growth on lower wall in non-air conditioned space
Mold colonies on underside of roof sheathing
Air conditioning units reduce moisture content in the air, or relative humidity. Despite humid summer weather, mold problems are more common in the winter when AC units run less. Proper air filtration through AC units also reduces airborne spore count. Building envelopes are porous and we must open doors and windows at some point, so spores will always be present.
Due to the widespread nature of spores, Oxygen, and cellulose in the built environment, the most important factor we can control is MOISTURE. In nature, water brings vegetation and wildlife, imagine a desert oasis. Similarly, moisture in the built environment may cause the growth of unwanted fungal life. Prevention of leaks is the best way to avoid unwanted moisture. Immediate dry-out of any leaks that do occur is imperative, which brings us to our next topic of remediation.
There are no industry mandated standards for fungal remediation protocols, although the IICRC standards gives some good general practices. The lack of set standards leaves some gray area where good professional judgement is required. First of all, testing must be performed and evaluated by a trained professional. IICRC states that significantly elevated indoor mold spore counts must be found to justify remediation.
I recently evaluated a case where a mold remediation company documented 4 elevated spores and recommended remediation. The American Industrial Hygiene Association (AIHA) states that indoor fungal contamination is likely if indoor air spore counts are significantly elevated over outdoor air spore counts. 4 spores did not constitute significantly elevated indoor air spore count and remediation was not warranted. This illustrates the need for independent evaluation of mold remediation documents proposals.
On the inspection depicted, we reviewed documents provided by the remediation company that depicted personnel cleaning an AC unit with air scrubbing equipment at their feet. Upon examination of the inner portion of the AC coil, we observed what appeared to be fungal growth. So, we tested it and the results came back positive for a common fungal genus. This case perfectly illustrates the necessity for independent review. A homeowner would probably never think to pop their head up under the AC coil to verify effective remediation.
Personnel cleaning AC unit
Fungal colonies in same AC unit coil
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