Often the ground elevation in a crawl space is lower than the grade outside. This sometimes causes moisture problems in a crawl space. Some indications of excessive moisture in this area are:
·Musty odor in the crawl space or living area of the home.
·Mold on the foundation wall, floor joists or soil surface in the crawl space
·Standing water under the house
·Excessive condensation especially on windows in the house
If evidence of excess moisture is found in the crawl space, have any leaking pipes repaired. See that kitchen, bathroom and dryer vents empty outside the house rather than in the crawlspace. Also, any crawl space air conditioner condensate drains should empty outside.
Water should not stand against the foundation on the outside of the home. To prevent this from happening, provide a minimum slope of 6 inches in 10 feet away from the home on all sides. This can be done by grading soil against the foundation wall or by lowering the elevation in the yard, or both. If needed a perimeter drain can be installed around the foundation to carry water away from the house.
A house should have gutters and down spouts with outlets on splash blocks or with horizontal extensions to discharge water on the ground at a point far enough away from the dwelling that it will not enter the crawl space.
Where the surface of the soil under the house is considerably lower than the outside ground, chances are good that it will be moist and there will be considerable evaporation into the crawl space.
A polyethylene (plastic sheet) vapor barrier on the ground in the crawl space can prevent nearly all evaporation. Plastic sheeting of 6 or 8 mil thickness will be tough and resist damage. Rolls of these sheets can be purchased at a hardware store or lumberyard. Roll the sheets on the ground in the crawl space overlapping the sheets by 4 inches and extend them 4 inches or more up the side of the foundation. The sheets can be sealed together using contractors tape or caulk, or sand or bricks can be piled on the sheeting to keep the material in place. Seal the sheeting to the foundation wall with caulk and furring strips or pile sand or bricks on the sheeting where it meets the foundation wall.
In older homes, plan to install a vapor barrier in several stages. Do not cover the whole ground at once but gradually over two weeks to allow the microenvironment in the crawl space to adjust to the change.
Condensation may occur on the bottom of this polyethylene sheet but this is not serious. The important function of this vapor seal is to prevent moisture from escaping into the air of the crawl space.
There is some controversy about whether it is necessary to vent the crawl space. If there is moisture in the crawl space, it should be vented until it dries out. When the crawl space is dry, it is not necessary to vent it if moisture sources have been sealed out.
To kill mold that is growing in the crawl space, make a solution of chlorine bleach and water (about 1 cup bleach to 1 gallon of water). Scrub the surfaces with the solution and dry quickly. If your under-floor insulation is contaminated with mold, proceed with replacement after you have cleaned and dried all surfaces.
If you have questions in the area of Family and Consumer Sciences, please call the Hall County Extension Service Monday through Friday, 8:00 a.m.-5:00 p.m. at 770-535-8290.
Debbie Wilburn is County Agent/Family and Consumer Science Agent with the Hall (770)535-8290 and the Forsyth (770)887-2418 County Extension Service.
Sunday
July 6th, 2025
1:16AM
