A Cautionary Tale of Jim, the DIY Homeowner Who Vented a Crawl Space

When it comes to maintaining a healthy home, homeowners can do about 50 percent, or half, of those needed project themselves. That’s good news for the handy types among us. Tools and materials are a do-it-yourselfer’s idea of fun. Add a bit of common sense, make a plan, top with a sense of adventure, and you’ve got a do-able weekend project.

The other 50 percent of home maintenance projects are the problem. Many require a grounding in the sciences and sometimes, engineering. Without that knowledge, a do-it-yourself (DIY) project can go terribly wrong.

Let’s take my friend, Jim. He’s gone to great lengths to vent a crawlspace as much as possible from outside air. He’s handy, well-intentioned. He’s considered the problem, come up with a solution to exhaust the air and reduce humidity. However, he’s unaware of the adverse effects his do-it-yourself fix is having on his home and its healthiness.

Let’s take a look at this disaster.

Jim’s goal was to blow moisture out from the crawl space, a worthy intention.

First, he installs exhaust fans in several of the foundation vents. Next, a screen is placed in a closed access hatch and the door is left open. At times, a large fan is positioned here to blow outside air into the crawlspace. 

Here we find the first flaw in Jim’s plan. Plenty of moisture is found in the warm, humid summer outside air here in Appalachia. What happens when you dump warm, humid air into a space where air and objects are well below the dew point? You’ve created a sure fire way to keep the crawlspace as humid as it possibly could be. 

After all that money and labor, imagine Jim’s surprise when he measures the results of that DIY project. The crawl space humidity measures a whopping 85-95 percent.

The situation gets worse. This humidity condenses onto the fibers of the fiberglass floor installation. The insulation, in turn, becomes soaking wet. When insulation is wetted, it fails to insulate. But energy conservation is the least of his worries.

The insulation also falls to the ground below under the weight of the water that the insulation has absorbed. Fiberglass is not his friend. Jim looks up and sees that the insulation, acted like a wet sponge. Nestled against the wooden floor joists, the moisture has compromised the wooden floor joists. As the joists rot, mushrooms literally grow out of the woodwork.

By the time Jim calls me, there’s so much water in the crawl space that water is dripping down the ducts, forming puddles.

What every Appalachian homeowner should know is that if their home has an air conditioning system with ductwork in the crawl space, then humidity will condense on the outside of the supply air ducts – similar to the water droplets that form on the outside of a glass of cold lemonade on a hot day.

The air ducts probably have a temperature of about 60 degrees Fahrenheit, which is below the outside dew point that day of 70.  

Let’s follow the chain of events to see what else I found.

Organic “soup” is foul, but bacteria love it. Bacterial scum pools of tan, orange, red, green, white and brown have begun to develop. If that’s not enough, molds now flourish on the surfaces above. The wooden floor joists are covered with forests of green, white, yellow, brown, and black colored molds.

This latter problem was the very thing that Jim was looking to prevent by doing this project in the first place.

Taking a look at the furnace and air handler came next. Metal cabinets, motors, and electronic circuitry crumble as they rust under the high conditions. The unit is still functional, but its lifetime of usage will likely be reduced.

Meanwhile, Jim’s wife mentioned that the hardwood floors were starting to cup and warp in places upstairs. The floor joists weren’t the only thing affected by all that humidity. Her allergies were also acting up, and she felt tired even after a full night’s sleep.

Interior bacterium, mold, and dust mites thrive when flooring or carpeting is a bit damp. Those wet joists were right below the bedrooms, where we need the air we breathe to be the cleanest.

This unfortunate series of unintended, adverse consequences resulted from simply venting the crawl space. I only wish Jim had reached out to me to talk through his original plan before he started.

Now, we’re implementing a new plan to straighten out this mess.

Do you know a “Jim?” A well-intentioned relative, neighbor, handyman, or service professional who thinks they have the right idea, but who really need a bit of guidance before they do more harm than good?

We can help!