How do I Seal a Crawl Space?

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  • Written By: N. Swensson
  • Edited By: Angela B.
  • Last Modified Date: 13 October 2019
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It can be necessary to seal a crawl space to prevent moisture, pests, and radon gas from entering a home. First, locate any areas in the crawl space that could leak and either seal them or install a pump to remove water. Be sure the door of the crawl space is adequate, replacing it if necessary, and install a vapor barrier on the walls and floor. A vapor barrier can be made from plastic sheeting or concrete. Finally, insulate the crawl space to help provide more efficient heating and cooling of the home.

The first step when you want to seal a crawl space is to repair any existing leaks and seal cracks or holes where insects or water could enter. Areas around plumbing and electrical lines, air vents, ductwork, and cracks in the foundation should be sealed with caulk and expandable foam. Sealing these openings can help to prevent moisture and insects from entering the crawl space.

Sometimes moisture is already present in a crawl space because of groundwater leaking through the foundation. In these cases, it may be necessary to install a sump pump to move water out. A professional contractor who specializes in basement drainage may be able to provide this service as part of encapsulating the crawl space. If flooding is a problem, consider using a backup generator so the sump pump continues to run during power outages.


After addressing moisture problems, the next step you should take to seal a crawl space is to make sure the door is airtight. Many crawl space doors are flimsy and need to be replaced with a thicker piece of wood or metal. In other cases, weatherstripping can be installed around the door to help seal the area.

One of the most important steps when encapsulating a crawl space is to install a vapor barrier. This usually involves placing thick plastic sheeting over the walls and floor of the space. The plastic can help to prevent moisture, pests, and radon gas from entering a home. It also helps to insulate the crawl space, making climate control more efficient. The sheeting should be securely attached to the foundation and properly sealed.

Using concrete to seal a crawl space floor is another option, but it usually still requires use of a vapor barrier. Finally, using foam insulation in the crawl space ceiling is another important way to prevent air exchange with the rest of the home. Following these steps can seal a crawl space and protect your home.


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