Unnecessary Panic: Mold

Unnecessary Panic!: Mold & Fungus In the Crawlspace

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I recently received a call from a Realtor who is selling a home. He asked if I could double-check the findings of another home inspection company that requested expert advice on some mold/fungus they found in the crawl space of the home. I gladly obliged.

After my inspection I wrote the following report:

Unnecessary Panic: Mold
Molds and Fungus thrive where there is cool, moist air. That’s why your crawlspace is a breeding ground for mold. When you remove the moisture and correct air condition ventilation issues mold will not grow.

“As per your request, I visited the subject residence today to evaluate mold or fungus growth on the floor joists.  I understand that a home inspector expressed concern about fungal growth on the floor framing, so the buyer is concerned that the fungus needs to be removed/cleaned/mitigated from the joists.  During my visit, I crawled to the four main corners of the crawl space and probed the floor system with an electronic moisture meter during this traverse.  I never obtained a moisture reading above 16%.  This is a perfectly normal moisture content and one that will not support fungal growth.   You can Google “moisture content of wood necessary to support fungal growth” and see for yourself.  I can’t speak for the home inspector who has raised concerns, or what his experience level is, but I can assure you that the floor joists beneath this home are no different than 90% of the floor joists I have inspected over the past three decades.

The home inspectors working for fees today seem to have one primary motive in mind: to cover their liabilities.  They many times cite the need for further evaluations by what they call other so called experts.  These home inspectors are insecure and inexperienced.  They need to carry a moisture meter with them under houses and probe the floor joists to measure wood moisture content.  If the moisture is less than 20% and the floor joists are structurally sound, like the joists at this home, there is no need to worry about any fungal staining that might exist.  Why and how can I say this?  Because ventilated crawl spaces throughout the Southeast United States allow high humidity and fungus spores to enter the enclosed space beneath the home.  During the summer months, when outdoor humidity is high, the hot/humid air enters the crawl space through the foundation vents and condenses on cool objects.

Unnecessary Panic: Mold
A moisture content of less than 20% indicates that your joists and beams do not have the necessary moisture content for mold or fungus to survive.

At this home, cool objects include the air conditioning ductwork, the ground and the overlying wood floor system, which is exposed to very cool temperatures due to air conditioning duct leakage.  As this moisture condenses on the floor system, it wets the wood.  Fungus loves wet wood.  As stated, fungal spores are beneath the home because they are in the air we breathe-the same air that gets circulated beneath the home.   These mold spores land on the wet wood and take root.   But this wetness is only surficial.  The wood joists are not soaked wet, it’s just a light film of moisture on the wood members.  Once the summer cooling season ends, and the A/C is shut off, and the outside air cools, and the humidity drops significantly, the cool dry air now flowing beneath the home dries out the floor joists.  Now the fungus goes dormant.  It’s still there and causing stains and scaring inexperienced home inspectors who frighten buyers, but it’s dormant.  It’s not growing or feeding on the wood.   It is not fair to ask the seller of this home to pay some pest control firm to spray Borate on the floor system. This is expensive and it’s ridiculous.

All that needs to be done at this home is to close-up the foundation vents during every air conditioning season and make sure the ground cover vapor barrier is spread completely over the underlying ground surface.  And it really helps to pay an HVAC contractor to better seal and insulate the A/C ducts so they don’t leak cold air!!!   This will stop the wet/dry cycle that exists every year, in every ventilated crawl space containing A/C ductwork in the SE United States, over their lifetime.

Please don’t pay for a Borate spray unless the buyer wants to pay for it. “


James A. Durham, P.E. 

Mold and fungus in the crawl space can definitely become a problem, but don’t be fooled into thinking that a Borate spray HAS to be applied in EVERY situation. Call JADE today for a crawlspace inspection and we can give you definitive answers to your crawl space problems! Call 256-318-0982 or contact us today.

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