Wet Georgia Crawlspace

January 01, 2006
January/February 2006
A version of this article appears in the January/February 2006 issue of Home Energy Magazine.
Click here to read more articles about Moisture Problems

Wet Georgia Crawlspace

I have too much moisture in the crawlspace of my 1971 single-level brick home in west central Georgia. Can you recommend a method to lower the moisture level?
        There is no plastic ground cover/barrier in the crawlspace. A 14-inch fan circulates air in the crawlspace (the fan is not located at a foundation vent; it just blows across the crawlspace). The foundation vents are open, including the screened crawlspace entry doors.There’s no ground/rainwater flowing into the crawlspace.There are no roof gutters on the home.
        The insulated ducts in the crawlspace have condensation on them; there is mold forming on floor joists in several places; and heavy moisture is collecting in several places on the floor joists and drips down. There’s no sign of standing water in the crawlspace, including none inside of the foundation wall, but the ground there is damp, especially along the inside foundation wall.The outside air was very humid last summer and temperatures have been in the mid-high 90s.
        Any information you could share would be greatly appreciated.

        A. Mickey, it sounds like you already know what your problem is and what is contributing to it. You need to keep moisture out of your crawlspace, particularly if you are going to put cold A/C ducts down there. If it is difficult and/or expensive to move the A/C ducts, here’s what you need to do:
        Cover the ground with a vapor barrier. A 6-mil poly from your local hardware store is fine for this and will make it much nicer every time you (or an electrician/plumber/cable guy) have go into the crawlspace.
        Close all the crawlspace vents.
        Stop blowing humid air into the crawlspace with a fan.
        Instead, blow (drier, conditioned) air from your house to the crawlspace. You only need a small fan for this once you have sealed all the crawlspace vents. Something like 100 CFM would be plenty.
        Add gutters. Get the water from the downspouts away from the foundation. The ground should slope away from the foundation as well.
        The above may not totally cure your problem if you have rain leaks or groundwater issues, but it will deal with the outdoor air as a moisture source.

California Building Codes Raise New Challenges

        Although readers of Home Energy magazine have known about duct leakage for several years, the issue has now reached the point where it is being addressed in building code requirements. Low duct leakage is now a requirement for new construction in California, Florida, and Washington, as it is for such federal programs as Energy Star Homes and Building America.These specifications have been relatively well accepted, because good duct construction is fairly straightforward during the installation process when ducts are easily accessible. Existing systems present a much greater challenge.
        In one of the biggest changes to hit the California HVAC industry, as of October 1, 2005, the state of California dramatically changed the requirements for installations of new furnaces or air conditioning equipment in existing homes. As part of any change out of HVAC equipment in certain climate zones, the ducts are required to be sealed to 15% of fan flow total or 10% of fan flow to outside. Thirdparty verification by a certified home energy rater is required on a sample of systems. Similar requirements must also be met in existing nonresidential buildings.
        Some systems may be difficult to seal to the 10% or 15% levels, so the code has an alternative requirement: Leakage must be reduced by more than 60%, and all accessible leaks must be sealed and verified through visual inspection by a certified HERS rater. Furthermore, all ducts that are outside of conditioned space must be insulated with a minimum of R-8 duct insulation and contractors are required to use only California Energy Commission-approved duct sealants. There are also new requirements for refrigerant charge tests or use of TXVs in air conditioners.

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