What is Hydrostatic Pressure?

Today we’re going to talk about hydrostatic pressure in the crawl space and why you should pay attention to it.

I’m going to be totally transparent. I am not an engineer, nor do I pretend to be an engineer, so all of you engineers out there, please feel free to comment on the ins and outs of hydrostatic pressure, but I’m going to explain a little bit about what I do understand about it in my own words. Okay?

Basically, the way I understand it, is hydrostatic pressure is pressure from the outside of the crawl space where the water in the soil is pushing against the foundation wall. The taller the dirt wall, the more pressure. Think about it like this, when you go scuba diving, the further you go down in the ocean, the more the pressure there is on your body from the water. It’s the same with hydrostatic pressure. If you’ve got six, eight feet of wall with dirt on the outside, and a much lower grade in the crawl space, the water is more likely to be forcing harder in through the foundation wall.

So that’s a layman’s terms way of explaining hydrostatic pressure.

Is Hydrostatic Pressure In Your Crawl Space Bad?

Should you care about hydrostatic pressure? Well, hydrostatic pressure can cause a humidity problem inside the crawl space, which can eventually lead to mold. If you’ve got a cinderblock foundation wall and you notice a white, chalky looking substance on the wall, you know you’ve got hydrostatic pressure. If you get enough hydrostatic pressure, you’ve got enough water to where it can eventually start to flood the crawl space.

The white, chalky substance is called efflorescence. Efflorescence occurs when the different materials that cinderblock is made from get pushed through the block because of the pressure from the water on the exterior of the foundation wall.

Another thing I’ve found over the years, is that home inspectors don’t like to see evidence of hydrostatic pressure on the crawl space walls. If you are looking to sell your house and the home inspector goes in and they see the efflorescence on the wall, even though you may not have standing water, you may get a ding on your home inspection report asking you to address the hydrostatic pressure.

Hydrostatic Pressure Solutions

So how do you fix it? You typically have to address hydrostatic pressure from the outside. You have to redo the outside foundation wall to keep that water from coming in.

I’ve seen instances where you’ve got enough hydrostatic pressure on the wall to ding on the home inspection report, but there’s no standing water. So most crawl space companies, if they see hydrostatic pressure on the wall, they’re going to say, “Oh. Well, you need a trench and a sump pump.” “I don’t have any standing water. Why do I need a trench and a sump pump?“

Just keep in mind that hydrostatic pressure can eventually over time, maybe years and years and years down the road will get worse and worse and worse and worse. Water will always take the path of least resistance. So you may one day have standing water on that wall that you’ve got a lot of hydrostatic pressure on now.

One of the best things you can do to address hydrostatic pressure is going ahead and installing a vapor barrier up the wall. Make sure you’ve got it behind foam board and vapor barrier if you’re encapsulating your crawl space, so that way as the hydrostatic pressure comes in, it’s being forced under the vapor barrier.

Also make sure you install a dehumidifier to control that humidity as it’s coming in. If you’re planning on staying in the house for a long period of time, I would recommend investing in a sump pump and a trench because most likely one day, you could be dealing with a water intrusion problem.

If you go ahead and encapsulate the crawl space, you plan on living there the rest of your life, and then in 15 years you’ve got to rip all the plastic out to put in a sump pump because you didn’t do it 15 years ago… It’s going to be more expensive to do that 15 years from now, than it is to do it correctly today.

I hope you found this information on hydrostatic pressure helpful! If you have any questions or comments feel free to let us know below.