February 2006 Edition

Crawl Space Mold?

The buyer’s inspector said "Your crawl space has mold growing on the framing." What do we need to do to eliminate the problem?
There is a reason for concern. The mold in the crawl space can enter the living space through your furnace ducts and through openings in the floor. Mold represents excessive moisture on the framing. The moisture typically enters from the ground and through the foundation walls. Most older crawl spaces have concrete block foundation walls and moisture will go straight through them. This is normally evident by moisture stains and white powder called efflorescense on the inside face of the walls. To remove the moisture requires a series of corrective actions.

Crawl Space

We recommend doing all of the following:
1. REMOVE THE SOURCE
First of all, remove any source of moisture if possible. If your house does not have gutters, install them. Make sure all downspouts terminate into drain pipes that carry the water away from the structure. Downspouts are the number one cause of wet basements and crawl spaces. Next, if water is running towards the foundation, re-grade to divert the water away from the house. Make sure all of the grading at the foundation slopes away from the house and falls a minimum of 6 inches in the first ten feet.
2. FOUNDATION DRAINS
Install a footing drain around the house to capture water that does seep in at the foundation. Dig down to the side of the concrete footing. Lay a 4 inch perforated drain tile and cover with a minimum of 4 inches of coarse gravel. On top of the gravel, lay a filter fabric to prevent mud and silt from clogging the pipe. Compacting the backfill will make it difficult for ground water to soak in. You can rent compactors at most building equipment rental stores.
3. SEAL THE FRAMING
Next, go inside the crawl space and look for holes or openings in the framing. Seal around all pipes, wires, ducts, anything that penetrates the framing. Also, caulk along the sill plates where they meet the foundation and along the top and bottom of the rim joist (see drawing). Either a good quality caulk or spray foam sealer will do . Your main goal here is to keep the moisture from sneaking in at the siding or around the wood framing.
4. INSTALL A FULL VAPOR BARRIER
A vapor barrier is needed over all of the foundation walls and ground to keep out the rest of the moisture. Use a minimum of 6 mil plastic that can be purchased at most home centers. Use 12 foot wide rolls to eliminate as many seams as possible. Before you install a vapor barrier, make sure the crawl space is clean of all debris and is dry. This may mean waiting for a dry spell which shouldn’t take very long in Atlanta. Never seal a wet crawl space. Pump out any standing water and use a dehumidifier if needed to help dry out the space. Fill in all foundation vents and seal them. After the crawl space is dry, run a sheet of vapor barrier along the walls and out into the floor four feet from the wall. You want the vapor barrier on the wall to be separate from the one that covers the ground. Anchor the top of the vapor barrier with a pressure treated furring strip. The furring strip should be approximately 4 inches down from the top of the wall. This will leave a view strip so you can visually inspect the wall for wood destroying organisms or what are commonly referred to as termites. Seal the end of the vapor barrier and furring strip with duct mastic available from any heating and air conditioning supplier. This will prevent moisture from escaping from behind the vapor barrier. Next, cover the ground, taking great care to cut around all pipes and supports. All joints should lap a minimum of 12 inches and must be totally sealed with mastic. Do not use tapes. Most tapes will peel off after a while.
While you are working in the crawl space, go ahead and insulate the framing with a minimum of R-11 fiberglass insulation and the water pipes with pipe insulation. The last thing you will need to do is make sure your door is solid, secure and weather-stripped. After going through all of this effort, you don’t want air leaking in around the door. Although a comparative study has not been made on the cost efficiency of sealing the crawlspace, I would be surprised if there is not a reduction in your utility bills.
The Princeville Research Project is an ongoing Advanced Energy project started in the eastern North Carolina town of Princeville. It has shown sealed or "closed" crawl spaces do a much better job of controlling crawl space moisture levels than do well-built wall-vented crawl spaces. While relative humidity in the wall-vented crawl spaces exceeds 80% for the majority of the spring and summer months, the Princeville closed crawl space designs control relative humidity below 65% during the same period. The research also shows that the homes built on closed crawl spaces save up to 15% on annual energy usage for heating and cooling when compared to the homes built on wall vented crawl space foundations.
Advanced Energy, a private nonprofit corporation in Raleigh, N.C., offers field tested solutions to moisture problems in its 2005 publication "Closed Crawl Spaces," by Bruce Davis, Cyrus Dastur and Bill Warren. Photographs, illustrations and sample designs supplement the text, which provides detailed instructions for designing and building a closed crawl space. The 75 page guide was funded by a grant by the U.S. Department of Energy and can be downloaded for free at the Advanced Energy web site www.crawlspaces.org. 

If you have a question, change of address, comment, home tip or would like to send Home Tips to your clients, send your letter to Home Tips, Christian Building Inspectors, Inc., 3697 Habersham Lane, Duluth, Georgia 30096. You can E-Mail your questions to us at rodharrison@christianbuildinginspectors.com. We reserve the right to edit questions for length.


Quote Of The Month

"The average person puts only 25 percent of his energy and ability into his work. The world takes off its hat to those who put in more than 50 percent of their capacity, and stands on its head for those few and far between souls who devote 100 percent."

Andrew Carnegie


A Tip Of The Hat To:

Donna Irwin

Coldwell Banker Residential Brokerage

4790 Sugarloaf Parkway, Suite 200

Lawrenceville, Georgia 30044

**** Thank You****


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