How to Fix Water Problems in the Crawl Space

Crawl space under a house
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Project Overview
  • Working Time: 2 - 3 days
  • Total Time: 2 - 3 days
  • Skill Level: Advanced
  • Estimated Cost: $100 to $500

Water in your home's crawl space is more than just an annoyance; it can have devastating consequences for your home's value. Standing water or even ever-present moisture in the air can create mold problems. At the extreme end, water in a crawlspace can lead to rot and decay that weakens structural members and makes major architectural repairs necessary. The presence of moisture can also foster termites, carpenter ants, and other insects that can damage your home. Water under the house attracts animals that you really want to avoid such as rats and raccoons.

You can fix the problem of water in your crawl space on your own. Because it is such a time-consuming project, you may wish to call a water remediation company to do the job.

When to Fix Water Problems in the Crawl Space

Water can sit in the crawl space for months, even years, giving a false impression that everything will be fine as long as you own the house. Over the long term, though, standing water can damage the house's foundation; wooden beams and joists will begin to rot; and various strains of mold can develop. You will be required to fix the problem when it comes time to sell the house. A future buyer will be unable to obtain a loan to buy a house with water problems in the crawl space.

Water remediation is a project best handled during dry months. While all of the work is done in protected environments such as in the house or under the house, water can continue to build up under the house and hamper work.

Identify the Source of the Water

When you find standing water on the ground, it is important to identify whether the source of the water is groundwater—water flowing in or seeping up from the ground—or if it is coming from above grade. Above-grade water usually comes from a leak in plumbing fixtures, drain pipes, or water supply pipes running in the space below the floor of the house.

Locate the access opening to your crawl space. This is sometimes an outside hatchway in the exterior wall around the crawlspace or a hatch in the floor, often located in a closet or utility area. Equipped with a good flashlight, sturdy work clothes, and plastic sheeting to protect your clothes as you crawl about, enter the crawl space and inspect every area—both the ground and the structural members of the house above you. Look for signs of standing, puddling water on the ground, and signs of discoloration caused by mildew and wood rot on the wooden posts, piers, and overhead structural members of the house.

Below-Grade Water Sources

Below-grade water problems typically become exaggerated during certain seasons of the year, especially rainy months. If your periodic inspections show that puddling water occurs more during these periods, then it is likely you are dealing with water entering the crawlspace from below grade—either as run-off from rain or from a rising water table.

In many parts of the country, the water table is quite high, and the rainy season can cause water to rise up into standing puddles in low areas of the crawlspace.

Above-Grade Water Sources

If the puddling water does not seem to be affected by seasons or weather, it is possible you are dealing with above-grade sources. This is most likely caused by plumbing problems in drain pipes or water supply pipes running beneath the floor in the crawl space.

If you notice that the pooling, puddling water is found directly below a tub, shower, toilet, or other plumbing fixtures, or beneath drain pipes, you are probably dealing with a plumbing-related water problem. The good news here is that plumbing problems can be corrected by a plumber, which will be less costly than dealing with groundwater issues.

Interior Water Issues

Simple humidity issues arise from water vapor transferring up from the ground into the crawl space. In this instance, you will rarely see puddling or pooling water, but there may be widespread evidence of mildew or mold on the wooden framing of the house.

This can be a severe problem in crawlspaces without vapor barriers and without adequate ventilation. But the solution is often simply to lay a vapor barrier over the ground, which is a much less expensive fix than dealing with major groundwater problems.

Safety Considerations

Working under your home can present many hazards. Dust, dried animal feces, black mold, and asbestos are only a few of the contaminants you might breathe in this space. Always wear breathing protection in the crawl space.

Many sharp objects might be in the crawl space since builders sometimes discard nails, utility knife blades, glass, and metal here. Be sure to wear heavy gloves, knee pads, heavy pants, and long-sleeved shirts or coats.

Before You Begin

Unless the crawl space can be accessed from the exterior, you will need to bring in materials through the house and down an access door. Make sure all areas you walk on are protected with plastic or contractor's paper.

What You'll Need

Equipment / Tools

  • Shovel
  • Tape measure
  • Wood stakes and twine
  • Flashlight


  • Bagged drainage rock
  • Sheet plastic or kraft paper rolls
  • Flexible perforated drain pipe
  • Plastic vapor barrier
  • GFCI outlet
  • Sump pump


The general process of controlling water in a crawl space involves setting up a perimeter within the crawl space and capturing any water that tries to infiltrate that perimeter. When water hits this border, it is diverted into gravel-filled channels and fed by gravity to a sump pump pit. The sump pump then pumps the water from the crawl space.

  1. Remove the Vapor Barrier

    If your crawl space already has a plastic vapor barrier, it should be removed, rolled up, and taken away through the access door.

  2. Dig the Trench

    Dig a trench around the entire interior foundation, using the foundation as a guide. A typical trench will be 18 inches deep and 9-12 inches wide, with a slope of one inch every 10 feet. The trench is typically between 8 inches and 24 inches from the foundation. If the trench is any closer to the foundation, it can undermine the foundation and the home itself.

  3. Lay the Drain Pipe

    Lay the perforated drain pipe in the trench. This will help collect water and direct it to the area where the sump pump will do its work.

  4. Fill the Trench with Gravel

    Cover the drain pipe with drain rock filling in the trench.

  5. Spread the Soil

    Spread any remaining soil from digging the trench evenly around the crawl space.

  6. Install a GFCI Outlet

    Either install by yourself or subcontract an electrician to install a ground-fault protected outlet in the crawl space.

  7. Install a Sump Pump

    At the low end of the perimeter trench, you will install a sump pump. This pump will automatically activate whenever water collects in the trench.

  8. Install a Discharge Pipe

    A discharge pipe will be routed from the sump pump to some appropriate discharge location outside the crawl space.

  9. Lay New Vapor Barrier

    Lay a new 6 mil vapor barrier over the ground of the crawl space to prevent vapor transfer from the ground.

  10. Install the Ventilation

    Where cross ventilation in the crawl space is inadequate, install new vents in the exterior wall of the crawl space. Very large spaces may be equipped with electric ventilation fans to facilitate cross-ventilation within the space.

When to Call a Professional

Water mitigation is not complicated or difficult to understand, but it is hard back-breaking physical labor. Most people opt to hire a contractor. Some factors make the job difficult for the do-it-yourself homeowner. For one, a GFCI outlet must be installed in the crawl space for the sump pump. This outlet must already be in place or you must contract out an electrician to install it. As a do-it-yourselfer, you can do the work by yourself, but it must be under an electrical permit and it must follow code.

In addition, it can be difficult to maneuver in a crawl space. A crawl space that is between 4 feet and 5 feet high is considered spacious, but even at this size it is very difficult to move around in. Many crawl spaces offer only 2 to 3 feet of vertical space. Hundreds of pounds of bagged drain rock must be carried into the crawl space, along with the perforated pipe.

There may be only one small door that allows access to the crawl space, and this door may be located in some inconvenient place, such as a bedroom closet or kitchen pantry.

Call the Right Professional

In wet regions where water problems are common, you will likely have several local companies that specialize in water mitigation services. Do not confuse them with basement drying and restoration companies, which come in after water problems have been fixed and deal mostly with hardscaping. Restoration companies clean and dry out the areas, but they do not fix the problem.

Search for companies that advertise for basement or crawl space waterproofing and drainage repairs. General contractors also can do this work for you, but make sure that they have done this type of work before.

Article Sources
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gay, Ron. 5 Steps to a Dry Basement or Crawl Space: a Guide for Homeowner & Professional: Also Included, Slab Foundations, All about Gutters, Mold and Bacteria. Welkin House, 2013

  2. Chapter 6: Housing Structure. Centers for Disease Control and Prevention