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Water in the Crawl Space

Water In The Crawl Space, How Bad Can It Be?


Richard Acree

During a recent Nashville Home Inspection a HABITEC Home Inspector observed moisture in a crawl space. If you have a crawl space, and you are like most people, you don't hang out down there much. So what's a little water in the crawl space hurt anyway? Maybe a lot. See the pix below. What's wrong?

HINT: What's that shiny stuff in the insulation?

ANSWER: Wait, that's water! Lots of water! That cannot be good, can it? Well, a little moisture in the crawl space is OK, but a lot is bad! And insulation should never be wet. If you start to pull the wet insulation down to see above, guess what you find. See below.

Pulling the insulation all the way out may reveal the whole truth, and it's not pretty. See below.

So how much water/moisture in the crawl space is too much?

I am not aware of any numerical metric to declare a crawl space too wet or not, but mushrooms in the crawl space has to be over the limit. 

Bottom line, keep those crawl spaces as dry as you can! Read on to learn how.

Water can access the crawl space from many different directions. Plumbing leaks, poor exterior grade, poor exterior roof drainage systems, poor moisture barrier installation, and HVAC ductwork condensation are some of the more common sources of water in the crawl space.

The common interior sources of water intrusion into the crawl space are plumbing leaks, poor moisture barrier installation, and HVAC condensation. Plumbing leaks happen but not that often really. The real culprits here are condensation from HVAC lines and a poor moisture barrier installation.

The condensation from HVAC ductwork usually occurs in the summer months when temps and humidity are at their highest. The best way combat this is to make sure your crawl space vents are open and flowing freely. While you are checking these vents, make sure the installation is intact. Cracks or gaps in and around these vents can allow unwanted guests like insects, rodents and reptiles!

 Another way to combat this issue is to increase the depth of the insulation surrounding the ductwork. Contact a HVAC technician to discuss that possibility.

Moisture barriers are the plastic poly that is placed over the floor/ground of the crawl space. HABITEC recommends a moisture barrier that covers the ground 100%, is overlapped at the seams, and is attached to the piers/posts and to the foundation walls.

If the moisture barrier does not reach the foundation wall openings in the moisture barrier allow moisture to evaporate into the crawl space from the ground below and can contribute to high humidity in the crawl space. This high humidity can then cause condensation from the HVAC ductwork and it can create a condition conducive to mold growth.

Exterior sources of moisture penetration include a failed roof drainage system and poor grade. Actually the two are related somewhat.

Homeowners should verify that their gutter/downspout/extension systems operate correctly. Overflowing gutters or disconnected downspouts deposit water directly at the foundation wall. Eventually some of this water makes its way into the crawl space.

Likewise flat or negatively sloped grade at the exterior of the foundation wall channels water from rain or sprinkler systems back towards the house. Again, eventually some of this water makes its way into the crawl space. HABITEC recommends a minimum 6" drop in grade over the first 10" of horizontal space/run away from the house.


Condensation drains from HVAC systems can deposit up to 7 gallons of water a day at the condensation drain termination. Drain Terminations that end at the foundation wall will again supply some more water to the inside of the foundation. See the photo to the right. These terminations should terminate away from the foundation wall and to terrain that slopes away from the home.

Making sure that your water management systems are properly designed, installed and maintained can go a long way to keeping your crawl space dry. Moisture in the crawl space is a serious issue and can create problems such as structural failure and mold.

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Thank you,

Richard Acree

Comments in this article are the copyrighted intellectual property of Richard Acree, President, HABITEC Home and Building Inspections, LLC, and contributing members of the Active Rain Real Estate network, and are intended to educate and otherwise assist home owners, sellers and buyers, building owners, sellers and buyers, realtors, real estate investors, property managers, and lenders in the process of owning, buying or selling homes or commercial buildings. HABITEC is a residential (home) and commercial building inspection company serving Middle Tennessee including Nashville, Brentwood, Franklin, Murfreesboro, Smyrna, Mt. Juliet, Hendersonville, Dickson, Belle Meade, Columbia, Spring Hill and more! In addition to building inspections HABITEC offers Environmental Services for mold assessments, radon testing and water quality analysis. Additional information about HABITEC can be found on our website at, or call 615-376-2753.

Richard Acree is the author of the HABITEC Home and Building Inspections Blog and founder of the ActiveRain Group Tennessee Home and Building Inspectors. All are welcome to join and see more blogs like this one.

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