How to Get Rid of Water in a Crawl Space

HVAC Crawl Space
jmrodri/Creative Commons/Flickr

Water in the crawl space: what fun!  Instead of putting your hard-earned money into something delightful--a new kitchen counter or bathroom flooring, you get to sink it into water mitigation.  Lucky you.

Is The Water Is Not Coming From Above Grade?  Answer:  No

Imagine that you live in a very wet area.  Under your house, in the crawl space, is a permanently wet area. After a hard rain, the wet area's diameter expands to about 10-12 feet.

The ground, instead of merely being muddy and spongy, begins to pool up with water, about 1/2" deep.  

During the dry months of June to October, the pool of water shrinks down but it never completely goes away. 

If this type of moisture sounds familiar--the kind of moisture that is everywhere but seems to be coming from nowhere--this article is for you.

If From Above Grade, That Is Likely a Plumbing Issue

The water might be attributed to leaking water supply or drain pipes.  If a water-related action happens within the house--someone takes a shower, dishwater runs, toilet flushes, bathtub drains--and more water develops in the crawl space, that is your likely culprit.  

Water Plus Lack of Light Creates Mold

With excessive water in the crawl space, you have the related problem of mold.

Mold loves to grow in places that have: a.) Moisture; b.) Lack of light. Both conditions perfectly describe a crawl space.


Mold will grow on the piers, joists, ducts, and other hard surfaces. But mold also grows on the "soft" materials, such as fiberglass insulation and on the plastic vapor barrier. When fiberglass insulation develops mold, it is impossible to clean off. Rip it out and replace it.

Who To Contact?

In water-prone areas, certain companies specialize in water mitigation services.

 Do not confuse them with basement drying and restoration companies, which come in after the problem has been fixed.  Restoration companies clean and dry out the area; 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.  

How Water Mitigation Companies Will Fix Your Problem

The process described here basically sets up a perimeter within the crawl space and seeks to capture any water that is trying to infiltrate the perimeter.

When water hits this border, it is diverted into gravel-filled channels and fed by gravity to a sump pump. The sump pump then siphons up the water and purges it from the crawl space.

  1. Protect: Unless you can access your crawl space from the exterior, you will need to bring in materials through the house and down an access door. You will need to protect all walk areas with plastic. Or, to prevent slipping, you can use builder's or rosin paper.
  2. Remove Vapor Barrier: Your crawl space may already have a plastic vapor barrier. Remove this and discard.
  3. Dig Trench: Dig trench around entire interior foundation, using the foundation as a guide. Trench should be between 8" and 24" from the foundation. If not, it may undermine the foundation.
  1. Lay Pipe: Lay down 3" socked flex perforated pipe through entire perimeter trench.
  2. Cover with Gravel: Cover with 1 1/2" drain rock.
  3. Spread Soil: What to do with all of that dug-up soil? Spread it evenly around crawl space.
  4. Install GFCI: Install a GFCI outlet in crawl space (the company will contract an electrician to do this).
  5. Install Sump Pump: At the low end of the perimeter trench, install a sump pump as recommended by manufacturer's directions.
  6. Discharge to Exterior: Sump pump to discharge perimeter trench water to outside.
  7. Install Vapor Barrier: Install 6 mil vapor barrier to prevent vapor transfer to crawl space.

Should You Fix Your Crawl Space Yourself or Hire a Company?

Water mitigation is not genius work but it is hard physical labor.  A few factors that make this project especially difficult:

  • Power:  A GFCI outlet must be installed in the crawl space for the sump pump.  Mitigation companies will not do this.  It must already be in place or they (or you) must contract out an electrician to install it.
  • Low Ceiling:  A crawl space that is between 4' and 5' is considered tall.  Even a "tall" crawlspace is very difficult to move around in.
  • Heavy:  Hundreds of pounds of bagged drain rock must be carried into the crawl space, along with potentially hundreds of feet of perforated pipe.
  • Tight Access Point:  There may be only one small door that allows access into the crawl space, and this door may be located in some inconvenient place, like a bedroom closet or kitchen pantry.

Cost Estimates

Cost differs according to where you live and the size of your house (and the size of your problem; bigger or even multiple sump pumps may be needed).  

One water mitigation project in the Seattle area:

  • 170' of perforated pipe
  • Drain rock
  • Single Zoeller 1/3 HP sump pump
  • Electrician installing GFCI

Cost:  About $5,000.

How Urgent Is This?

For anything dealing with water and enclosed spaces, the easy, prudent answer is always:  do it immediately.

Realistically, you do have some leeway.

Water can sit in the crawl space for a long time without having any adverse effect on your house.  In the short term, you are dealing with mold on hard surfaces and perhaps some insulation needs to be removed and replaced.

However, over the long term, you are in for trouble: standing water can damage the house's foundation; wooden beams and joists begin to rot; and harmful strains of mold can develop.  

At the very least, you will be required to dry up the crawl space when it comes time to sell your house.