There are several reasons for microbial growth to occur in the crawl space. Microbial growth comes in various forms and colors. The coloration of the mold really doesn’t matter to the context of health related problems or damage to the structure.
In order for mold to grow there are three basic requirements. First, there must be moisture (humidity in excess of 61% or moisture content 21% or higher), second, is oxygen (without that nothing living can grow), and the third and final variable is organic material (wood, cardboard, paper, etc…). The most prevalent of these variables as it pertains to this topic is water/moisture/humidity with a structure.
Below is a list of the causes for mold growth to occur in a crawl space… withstanding the most common misconception that most make when identifying mold.
Efflorescence (a white powdery substance left behind on concrete, stone, brick, etc) is a telltale sign of moisture in the crawlspace; primarily seen in the foundation walls and footings.
This is evidence of seepage(vapor drive/water pressure), but it is not mold. It can be easily removed, although it is not absolutely necessary. So, if you have efflorescence, it is a sign or symptom that there is likely a water or moisture problem that could be a reason for the mold, but it is not mold itself. Now the list:
- A high water table (seasonal or not) – Not all land is permeable thus retaining water during heavy periods of rain, snow, or natural spring ascension. If the water table is too high then the conditions are present for standing water, high humidity, and posts potentially getting wet. This creates a conducive condition causing proliferation of Microbial growth (mold).
Damaged, Broken or disconnected drain pipes – Older drain pipes, due to degradation, and tree roots can cause piping below grade to break or stop functioning the way they were intended. This can allow seepage into the crawlspace in the form of water or create a condition that will cause increased water pressure/vapor drive causing humidity to skyrocket.
- Leaking or broken downspouts and gutters – This results in water build up along the structures’ foundation wall. As concrete is porous, the water will saturate the foundation wall, and ultimately push or leak into the crawl space. This is especially problematic for unprotected/unsealed foundation walls. Or structures that are slab on grade.
- Foundation cracks in the wall and footing – This expands on the reasons above. Cracked or damaged foundation walls allow moisture to seep into the crawl space.
These cracks can allow water and moisture as well as pests into the crawl space creating elevated humidity directly in contact with posts, beams, and other structures in the crawl space.
- Poor laundry and kitchen venting – When kitchen exhaust fans and laundry vents are installed to vent inside the crawl space, mold can grow due to excess humidity and high temperatures being pushed out directly onto or near wood.
- Wall vents – All homes with crawl spaces use exterior wall vents to encourage air flow/air exchange through the crawl space. However, we know that this can contribute to moisture and elevated humidity within the crawl space.
Here is how it happens… During the winter, the moist cool air enters the crawl space. In the summer, warm air comes into the crawl space. In both scenarios contact with the surfaces inside the crawl space causes condensation and eventually mold.
Also, some homes are under-ventilated or their vents are blocked or impeded by decks, landscaping, or patios. If there is a negative grade towards the home then water can literally run through the vents into the crawl space itself.
- Leaks from the Bathroom – Leakage from a sink, toilet and shower into the crawl space is very common. This often results in saturated wood and insulation followed by mold growth issues.
- Pipe leaks – Older copper or galvanized pipes will get pin-hole leaks, leak from failed joints, or sometimes just burst.
- Storage in crawlspaces – Although not a cause per se, storage in crawlspaces certainly contributes to mold, especially when it is stacked against a bare foundation wall, floor or on a dirt floor preventing proper air flow. The worst is with cardboard boxes or and organic/paper materials.
Mold loves cool, dark locations, like crawl spaces because they take longer to dry and generally have a higher humidity level year round.
Of course there are certainly other reasons for mold to be found in crawl spaces, but the ones mentioned above are the most common reasons why mold is present.
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