This article is by our contributing expert plumber, Mike Baker.
As a service plumber, I've spent countless hours crawling, walking, stooping, low-crawling, and head banging in more crawl spaces than I can count. Aside from dead mice and cat carcasses, the most consistent problem I find in crawl spaces is moisture. A little water in a crawl space can be fine, but too much can become a serious problem.
Is It Normal to Have Moisture in a Crawl Space?
Please keep in mind moisture in the crawl space is actually very common. In most cases, people don’t worry about a little condensation. When it becomes more than a little, it's something that needs to be dealt with.
Story time—I once had a call to check a sewer smell in a guest bath in a rental condo in a resort community. When I arrived, nobody was there so let myself in as per the property manager.
I found the bath in question and sure enough, it smelled like sewage.
I searched the bath and found no leaks or reasons for the smell. Off to find the crawl space I went.
Once I was in the crawl space the smell was definitely stronger. As I shined my flashlight across the crawl space, I found a clean, well-kept crawl space with a nice clean moisture barrier, but I had my suspicions.
I crawled over to the part of the crawl space where the guest bath sat above, reached across the concrete barrier with a gloved hand, and poked the moisture barrier.
It moved like a waterbed.
Turned out that the drain line just above the barrier and just below the guest bath had blown the cleanout cap off the main drain line for that bath. Every time someone flushed it was dumping into the crawl space and making its way under the crawl space moisture barrier.
How to Get Rid of Moisture in Your Crawl Space
Let’s talk about a few ways to get rid of water in your crawl space.
The question for you then is how much water or moisture do you have?
Is it a moist concrete wall?
Is it slow condensation in the crawl space in the summer that causes water to drip from the bottom of the floor joist?
Is it the constant puddle way in the back of the crawl space that never seems to go away and makes it smell so musty and wet? Is water in the crawl space after a heavy rain normal?
Did the spring runoff just flood your water heater and snuff the pilot light in your crawl space?
Whatever your level is makes a difference in the way you attack it.
Where it's coming from makes a definite difference as well.
Dehumidifiers are great for removing slight moisture from the air and providing a dry space. Of course, you don’t want it too dry, but comfortably dry.
No musty smell or the feeling something is crawling on you when you’re in the crawl space should be sufficient. Just be sure to read the directions for the model you purchase. That should walk you through the process of setting it up for your space.
Make sure when you use a dehumidifier that it's rated for that application.
Crawl Space Fans
Crawl space fans typically fit in the crawl space vents found in the foundation. Many of them have timers for certain times of the day so you don’t hear their smooth purr while you try to sleep.
Crawl space fans are also an inexpensive fix and can aid in drying out a wet crawl space.
Let’s talk about the big deterrents to crawl space moisture now. These can be expensive, but they can also be done by you rather than a contractor, bringing your cost down considerably.
Moisture barrier material is one of the most helpful things you can put in a crawl space. The plastic keeps the moisture on the ground and not on the bottom of the floor joists.
These barriers come in a range of thicknesses. The general plastic sheeting you get at the hardware store will hold up just fine but may tear easily, whereas other plastic can be purchased you could drive a tank over without any problems. This is the plastic typically used for radon mitigation but will work as a stand-alone barrier.
Crawl Space Wall Insulation
Insulation does much the same thing that moisture barrier does only for the concrete walls of the crawl space rather than the dirt floor. Its plastic backing makes it easy to roll out and hang along the outside walls of the crawl space.
Crawl Space Vents
Vents are vital to crawl space air movement, provided you're aware of their presence. Keeping them open in the summer is important to air out a crawl space and closing them in the winter is important to keep the crawl space warm
If I had a nickel for every hose bib I've replaced in a crawl space because a vent was left open and the line froze... well, you get the point.
The nice thing about crawl space vents is that you can open and close them from the outside.
Crawl Space Waterproofing
Let’s talk about how to stop water from getting into your crawl space.
I once looked at a house basement that was unusable to the point that they had cast a concrete lip around the outside walls, inside the basement, to make a trough of sorts to catch all water coming into the basement from ground water.
This water moved along the walls to a sump pit that was actively emptying every two-three minutes.
That was a lot of water.
Upon further investigation, I found the house sat in a floodplain. How they ever got a permit to put in a basement was mind-bending, but here it was.
So, this brings me to sump pits.
Crawl Space Pits, Lifts, and Pumps
Let me take a moment to explain a big difference. There are two types of pumps and pits.
The first is a sump pit. This pit takes ground water and moves it through a hose or a drainpipe to a site outside the crawl space or basement. It never, I repeat never ties into the sewage drain system of the house.
The second is a lift station, and although it looks very similar to a sump pit it has a very different purpose. The lift station pump and pit are designed to be tied directly into the sewer drainage system. This allows the homeowner to add sinks, toilets, or bathtubs to a level of the house lower than the main sewer would allow for. It takes the sewage from these lower fixtures, grinds it in the lift pump, and eventually shoots it to the main sewer via the pump. It does not serve ground water.
So why the explanation?
Many people will walk into a hardware store and ask for a sump pump when their lift station pump goes out, and they are sad when they overpay, get home and pull the pump only to find that they need to go back to the hardware store.
Don’t be that guy.
Back to the sump pump. If you have excessive ground water and your water tables get high in the spring due to runoff, or if you get large amounts of water during rainstorms then the sump is what you want.
You can use anything from a five-gallon bucket with holes you have drilled to a pre-made sump pit that comes with holes already.
It's up to you. Hire the kid down the street to dig the hole in crawl space or roll up your sleeves and ‘get er done!’
Sump Pump Tips
Things to keep in mind when putting in your sump:
Try not to place the sump under a bedroom or any other room of the house that needs to be a quiet space (need I say why?).
Don’t be sloppy about running the hose to the outside. When I run a sump pit hose in a crawl space, I always hang the hose along the bottom of the floor joists and try, if possible, to grade it toward where it exits the crawl.
Take your hose or drain out a crawl space vent. This will make installation easier for you, and you only need to sneak it through a corner of the vent so that you’re not inviting vermin in. If you don’t have a crawl space vent, then you will have to drill a hole to get out of the crawl space.
Make sure the hose takes the water at least ten feet away from the foundation. Any closer and you’re going to be pumping the same water again.
Try to put the sump in the low point of the area affected. This way all the water should move toward your pit.
If possible, get the whole pit in the ground and don’t leave any sticking up, thus utilizing the entire pit. There are some areas where the rocks are terrible, and you just can’t get it down all the way. I get it, just do what you can.
Place a brick or two in the bottom of the pit and set your pump on top of them. This will keep rocks on the bottom of the pit and not in your pump.
Make sure the pit is free of debris when you place the pump.
Finally, make sure you have an outlet nearby. I know you're the hardware king or queen and you have at least three fifty-foot extension cords in the garage that will make quick work of that. NO, NO, NO. Always try to be close enough to plug in directly when you can.
I wouldn’t suggest anything longer than a twenty-five-foot extension cord If you must. Too much extension cord can get hot and start a fire.
When I was in Iraq in 2005, we had a tent that caught fire and burned to the ground due in large part to too many extension cords. The real problem was it was the munitions tent—the tent with all the ammo, and some explosives.
Needless to say, that was an exciting evening, but I digress.
Crawl Space Water Removal
So, you still have excessive water in your crawl space.
Let’s talk perf pipe.
Perf is short for perforated. It means the pipe is flexible and has premade holes for drainage.
The way it works is professionals dig down to the bottom of your foundation and install perf pipe all the way around eventually directing it, in a trench, away from the house.
Ground water hits the perf pipe and makes its merry way away from your foundation, away from your crawl space, and ultimately your wallet.
Of course, the cost of all these things will vary depending on your area of the country. It could range from a couple hundred bucks if you DIY, to a few thousand if you have a get a professional involved (and no, I will not come do it for you).
So now that I have completely freaked you out let’s talk about easy fixes.
If you have a newly constructed home and you find moisture in the crawl space, don’t panic. Some new houses are very tight, and during construction, water can get in from a rainy day or a hose and just never dry out.
Open the crawl space for a couple of days and just let it air out. Keep an eye on it and it will probably disappear.
However, if you have an older home, such as I do, take some time, and make sure all of the places that pipes or vents go through the foundation are adequately sealed so nothing from the outside can come in.
Should I Use Lime to Dry Out a Crawl Space?
Some people use lime to dry out a crawl space. My professional opinion is that’s not necessary and if you do choose to use lime make sure to wear the proper PPE when doing so.
Should I Put Sand in My Crawl Space?
Let me tell you that whether sand has a legit purpose as far as drying goes I don’t know, but I would much rather move around in sand than over rocks. Sand is a wonderful crawl space addition if you ever have to do work down there.
Your knees will thank you.
Well, we have talked about a few points. All the way from opening the space to let it dry, to digging the foundation to use perf pipe.
The point is, moisture doesn’t have to be your nemesis. It can just be another maintenance point for your home. One that's well regulated either by a sump pump, a dehumidifier, or a moisture barrier. In some cases, maybe all three. Still, it's within the wheelhouse of “doable” by you or your favorite professional.