How Your Dirt Crawl Space Affects Your Home

Water can enter a crawl space under the footing, through the block walls, cracks and openings or from plumbing leaks. Once in your crawl space, it sits there in pools (or in some cases, we refer to it as a lake). The exposed earth also contributes a lot of water vapor into a dirt crawl space.

The earth is damp, and as the damp soil dries, the water vapor flows upward into the house by what is called the Stack Effect. A house’s natural tendency is to draw air in from the crawl space and lower levels, and then upward into the living spaces.

Building scientists say that 30% to 50% of the air you breathe on the first floor is air that came from the crawl space.

Therefore, whatever is in your crawl space air is in your house and affecting you. If there is mold in the crawl space, there are mold spores upstairs. If there are damp odors in your crawl space…you guessed it…there are damp odors upstairs.

Previously the tactic was to add vents to a crawl space with the idea that air will flow in through the vents on one side and out through the vents on the other side. These vented crawl spaces, instead of becoming less damp, end up being more wet. Rather than letting moist air out, a house sucks moist air in, and then up into home!

Air that flows in through the crawl space vents brings its moisture with it. When air is heated or cooled, its relative humidity changes. The relative humidity of air goes up by 2.2% for every degree we cool it. Crawl spaces are cool due to the earth averaging a temperature of 55 degrees year round. When warm humid air enters into a crawl space, the air is cooled, and the relative humidity goes up. This high relative humidity leads to sweating HVAC ducts, mold, rot, and energy loss.

To eliminate your vented dirt crawl space from having any negative effects on you home.

1. Fix the ground water leakage.
2. Isolate the house from the earth.
3. Seal the vents and other outside air leaks.
4. Condition or dehumidify your crawl space air.

The CleanSpace® System meets all the criteria for fixing your dirt crawl space.

Spray Foam Does Not Solve Crawl Space Moisture Issues

Mold growing on crawl space floor joists.

Mold growing on crawl space HVAC ducting.

Sweating (or should I say raining) HVAC system in crawl space

So how old do you think this house is? 10 years, 5 years, maybe 2 years old.

Not even close- try 6 months! This customer was not so happy to find these conditions in the crawl space of their newly built home.

As discussed in my previous post, spray foam insulation on the subfloor does not address the main issue in a crawl space- moisture from the dirt beneath the home. The wood members in the crawl space are still exposed to ground moisture. There are only two primary ingredients needed for rot and mold to thrive: one is organic material, like the wood beneath a home, and the second is water.

Wood + Water = Mold & Rot

Also, because the crawl space is still vented, hot humid air is drawn into the crawl space causing the HVAC ducting to condensate. This creates more moisture, and more mold growth! Not only was the mold evident in this particular crawl space, but the air quality testing inside the home also revealed high levels of airborne contaminants.

So, the only avenue to preventing structural damage, condensation and poor indoor air quality is to eliminate the moisture by installing a CleanSpace Encapsulation System.

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Spray Foam vs Encapsulation

Very often, we come in contact with customers who choose to use spray foam insulation on their crawl space sub-floor as a solution to fix their damp crawl space, versus an encapsulation system. Most lean towards that option due to a difference in cost. But are they really saving??

First, let me ask...along with installing foam insulation, what are you going to do to solve the moisture issue in your crawl space?

Spray foam insulation on the sub-floor does not address the main issue in a crawl space- moisture from the dirt beneath the home. The wood members in the crawl space will still be exposed to ground moisture. There are only two primary ingredients needed for rot and mold to thrive: one is organic material, like the wood beneath a home, and the second is water. Replacing the wood in a house is practically impossible, and very costly. So, the only avenue to preventing structural damage and those musty smells is to eliminate the moisture by installing a CleanSpace Encapsulation System.


Can you see the water dripping from the insulation and floor joists? Mold is also growing on the wood (the black stuff below).

A local spray foam contractor recently told me that they had a previous job in which the foam insulation that was applied to the subfloor actually locked in the moisture in the crawl space and created a bigger moisture and mold problem in the crawl space. Not the outcome they expected!

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Second... foam insulation applied on the subfloor renders the wood members unaccessible or "no longer visible" for an inspection.

Some pest control companies will void your termite warranty if the sub-floor wood is no longer accessible or visible for an inspection. Check with your pest control company before choosing this option. (With the CleanSpace system, our liner is installed a minimum of 1 block down from the top of the wall so that termites cannot get into the framing without being seen.)

I recently spoke with a customer that stated her friend had her house inspected for a pending sale. She was requested to cut out and remove some of the foam insulation so the home inspector could visually inspect the sub-floor wood members in the crawl space WOW! I bet that customer didn't plan on spending all that money to foam insulate their crawl space and to later cut it out. Ouch!

A more effective approach to spray foam insulation is to insulate the foundation walls, rather than the sub-floor, provided a proper encapsulation system has been installed.

As stated on the U.S. Department of Energy's website, to effectively insulate your crawl space for energy efficiency and to create a comfortable home, you need to properly control moisture in your crawl space.

Our goal at Lowcountry Basement Systems is to fix your damp dirt crawl space...FOR GOOD!

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