Got Mold? Part 2 – Crawlspaces and Moisture


Crawlspaces – they are some of the nastiest places around your home. Usually they’re filled with cobwebs and dust. They’re too low to move around in comfortably. And often, they’re filled with moisture, mold and wood-eating insects.

Because of this, most people avoid them. I had the misfortune of being the guy who spent every working day in these spaces until my knees and back deteriorated to the point that I couldn’t do it any more. So I’ve seen a lot of *yuck*. I’ve seen floors that were about to collapse. I’ve seen standing water. I’ve seen more rotting, dead mice than I ever wanted to. And I’ve seen mold. Boy, have I seen mold.

Unfortunately, the picture above is more typical than not. Most people’s crawlspaces are moist enough so support mold growth on the paper backing of the insulation between the floor joists. By the way, did anybody ever tell you that mold loves cellulose (i.e. paper)? So that insulation you put down there is a perfect place for mold to grow. Once it does, it basically eats the paper and your insulation falls down. Now you have a big, soggy piece of fiberglass sitting on the ground – mice love it, so they’ll use that as nesting material. It gets really nasty.

Mold 101

Remember what I wrote in earlier postings? Mold is everywhere and mold loves humidity. Give them proper conditions for growth and they WILL grow like crazy. And when they grow, they need to eat. Google “dry rot” and you can read more articles than you want about the topic. Here’s one.

Why Crawlspaces?

Most crawlspaces have been built incorrectly since the dawn of time. Or at least since builders started getting cheap and building crawlspaces instead of a real basement.

Let’s start with the worst type of crawlspace – the dirt floored crawlspace.

What is dirt? Well, technically, it’s basically a big sponge. Dig down a couple feet outside and what do you get? Damp soil. Damp means water. That water travels through the “sponge” and into your crawlspace. Then what? Well, physics dictates that water will move from damp spaces to less damp spaces until the two are at the same humidity level. So the moisture in the ground “wants” to evaporate and saturate the air in your crawlspace.

Unfortunately, since there’s an infinite amount of moisture in the ground, there is continuous supply of moisture moving from the ground into your crawlspace. This leads to the Sisyphean task of trying to dry out a crawlspace with a dirt floor. (You remember Sisyphus – he was the guy damned to roll a boulder up a hill for eternity and every time he made progress, the boulder rolled back to the bottom).

So what do you do? Most people will Google it, and go to the first link. They’ll then be confronted with a bunch of bad advice from idiots who don’t know physics, moisture dynamics, or the first thing about why and how problems arise.

Instead, use this search on the BuildingScience.com website. Joe and his crew are building scientists – they actually understand the problem. So don’t pay attention to what anybody else says on a discussion group, go straight to the source.

Since you’re still here reading, I’m assuming you looked at BuildingScience and decided it was too technical, so you want to hear about how to fix the problem in plain English.

So here you are, stuck with a damp crawlspace and you want a solution. You’ve tried a dehumidifier and ventilating the crawlspace, and all that happened was your electric bill went up $100. Maybe you got lucky and it dried out until the next rain, at which point you ended up with puddles but you were still out $100 and were no closer to a solution. Now what?

Ok – you have to do a little detective work. First off, if you’re getting puddles in your crawlspace, you’re either built on a natural spring, or the drainage around your home isn’t done right. Pray that it’s not a spring, because I can’t help you there. Sell your house and move, now….

Let’s assume that it’s a drainage problem. Walk around the outside of your house looking for drainage problems. For example:

That is the number one cause of water in the basement or crawlspace – the downspout isn’t attached or is dumping water right onto the foundation walls.

So the first thing you want to do is to make sure your gutters work properly and the downspouts drain at least 6’ away and downhill from your house. Don’t take shortcuts! You have to get the gutters properly draining away from your house.

If you’re serious about it, you’ll have the gutters tied to a drainage system going to a dry well far away from the house.

Why is this so important? Because, when it rains, your gutters are trying to dump thousands of gallons of water and if you dump that much water around your foundation, it’s going to come into your house, which will raise the humidity and lead to moldy conditions. Not just in your crawlspace, but maybe in your attic and everywhere else. Proper drainage is key.

The next bit of detective work requires that you get muddy and wet. I know, you don’t want to get yucky, but tough it out. It’s better than having your house collapse due to all the water and mold rotting out your crawlspace.

Go outside during a heavy rain and walk around the perimeter looking for puddles. Take pictures so you know every place things aren’t right. This might be caused by gutters overflowing or poor grading or local depressions in the soil. 

Then, go inside and look at the basement and crawlspace walls. Do you see any streaks on the wall or other signs of moisture?

Maybe you’ve got something like this? That’s usually not a good sign!

Just use your head! If you don’t want water in your basement/crawlspace, keep it away from your house to start with. Note every place that doesn’t look right. Every puddle outside. Every water streak inside.

You may have to have some landscaping done. The soil around your house must slope away from the foundation or the water will get in.

So this is all step one – keep the water out in the first place. For most people, properly grading the ground and fixing the gutters will do the trick. If that doesn’t work, come back and read my next post. I’ll talk more about this topic. Until then, go work on your gutters. Please, please, don’t do this:

If you do this, you may as well just put a hose in your crawlspace and turn on the faucet!

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