December 2000 Edition

Damp or Wet Crawlspace 

Our crawlspace has mold growing on the framing. Is this a problem and what can be done to eliminate it? 
Mold represents excessive moisture on the framing. If the moisture level reaches 20%, wood decay could begin. As bad as that seems, structural damage is not the worst thing that can come out of a damp and moldy crawlspace according to John Tooley, a building science specialist with Advanced Energy of Raleigh, NC. "A lot of fungi you find down there are not your friendly bread mold type. Some of it will land you in the hospital. It’s pretty scary when you find leaky ductwork running through an environment like that, transporting moisture and spores up into the rest of the house." Tooley’s warning coincides with growing public health concerns over fungi and the mycotoxins they produce. Of particular concern at the moment is a fungus called stachybotrys chartarum, which has been associated with iodiopathic pulmonary hemorrhage in infants. Some health officials believe that the worrisome rise in asthma and allergies in the U.S. is related to poor indoor air quality, with fungus spores playing a leading role.
Crawl Space
To remove moisture and dampness in the crawlspace requires a series of corrective actions. We recommend doing all of the following:
First of all, remove the 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 crawlspaces. 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.
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.
Next, go inside the crawlspace 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. 
A vapor barrier is needed over all of the foundation walls and ground to keep out the rest of the moisture. Before you install a vapor barrier, make sure the crawlspace is dry. This may mean waiting for a dry spell which shouldn’t take very long in Atlanta. Never seal a wet crawlspace. 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 crawlspace 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 mastic. 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 must be totally sealed with mastic.  
While you are working in the crawlspace, 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. 
Despite the potential for trouble, crawlspace construction is gaining popularity in some parts of the country, because it cost less than building a full-size basement while still providing an out-of-the-way place to put plumbing, electrical wiring and ductwork. "It’s an okay way to build a house so long as it’s done right," say Tooley. "The problem is, it’s usually not." Tooley and other building scientist have been working for years to educate builders and code officials on the right way to build a crawlspace. John Tooley can be reached at Advanced Energy, Raleigh, NC. 919-857-9000.
Excerpts from The Journal Of Light Construction

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