How to Remove Moisture From a Crawlspace

Home crawlspaces are probably the least visited areas of most homes. They are designed to provide a natural air barrier between the main floor of a house and the earth below. Due to their being dark, confining and not easy to access, maintenance and inspection is often ignored. This can lead to circumstances developing that cause flooding or other moisture buildup and promote mold, infestation or wood rot. Removing existing moisture and safeguarding against future moisture buildup is crucial maintenance that shouldn't be overlooked.

Things You'll Need

• Topsoil
• Vents
• Polyethylene plastic
• Plastic seam tape
• Utility knife
• Tape measure
• Sand
• Insulation
• Insulation hangers
• Staple gun

Instructions

1. Inspect the crawlspace for cracks or holes in the foundation walls and make any necessary repairs. Check water piping and drain pipes for leaks that may add moisture to the crawlspace. Clear any debris or materials that shouldn't be in the crawlspace.

2. Verify that the ground around the outside base of the foundation slopes downward slightly to keep water runoff from collecting near the house and possibly entering the crawlspace. If necessary add soil to create a slope for water to be drawn away from the house.

3. Add vents to allow proper airflow. Local building codes set the number of vents required, but some older homes don't have enough or sometimes any at all. A home inspector can recommend the proper amount.

4. Lay down a vapor barrier over the floor of the crawlspace using 4 to 6 mil polyethylene plastic sheeting. Seams should overlap at least 6 inches and be taped with plastic sheeting tape. Extend the plastic up the walls from 6 to 12 inches.

5. Add a 2-inch layer of sand over the plastic to help reduce moisture buildup on the plastic and protect against rips or tears. In some homes with difficult-to-access crawlspaces, this step may be impossible to perform.

6. Place rolled insulation between the joists of the floor above the crawlspace with the paper side up against the wood floor. Use joist hangers to hold the insulation in place.

7. Cover the joists and insulation with the same plastic sheeting as used on the ground, and staple the plastic to the joists to create a vapor barrier over the insulation.

Tips & Warnings

• Seal the vents in summer, insulate them with a sheet of foam insulation in winter, and open them to promote airflow in the spring and fall. This will remove any moisture accumulated while they were sealed.

• Use a waterproof sealer on the outside foundation if it is prone to leaks into the crawlspace.

• Use eye protection, gloves and a mask when working in a crawlspace.

• Check often for problems in the crawlspace. Leaky pipes or seeping foundations can appear suddenly, and it is always better to catch such issues as early as possible.

References

• "Home Maintenance For Dummies"; James Carey and Morris Carey; 2009