Crawl Space Moisture Barrier: Essentials to Know February 28, 2019 – Posted in: Blog

Crawl spaces are often dirty and damp, mainly due to their exposure to water and moisture. This makes it a perfect environment for mold, mildew, rust, and insects to grow. But you can prevent this unwanted growth from thriving if you invest in a crawl space moisture barrier.

This is the barrier that stops moisture coming from the dirt floor from being absorbed by your crawl space, lowering the air quality in your home. The moisture barrier is a plastic material or foil sheet that effectively prevents vapor from penetrating into the crawl space.

Crawl Space Moisture

The moisture in crawl space under house usually comes from three main sources, including bulk water, outdoor air coming in through the crawl space vents, and moisture from the ground.

Water usually gathers in the crawl space due to plumbing leak or drainage blockage. The longer the water stays stagnant in the area, which is bound to happen because you rarely visit crawl spaces, the worse the moisture problem will get. The next time you check your crawl spaces with this amount of moisture under the house, don’t be surprised to see floor joists growing spores and getting worse if the humidity in the area is above 70%.

Uncovered soil, even ones that look dry, still releases moisture into the air and into your crawl space. This is especially true among old houses since new ones already get vapor barriers placed on the ground. The vents in your crawl space are the perfect gateway from vapor from outdoor air to come in, raising the area’s relative humidity to unhealthy levels.

Crawlspace Moisture Control

Proper moisture control in crawl space is necessary if you don’t want to end up with the negative health effects caused by mold and mildew, rot, and rodents and vermin, not to mention the reduction in your house’s resale value. Even before the effects of moisture take a hold of your house, effective under house moisture control can help your property pass property inspection and avoid driving away prospective buyers. Fortunately, there are several crawl space ground cover for moisture control tools and techniques that can be used.

Acceptable Moisture Levels in Crawl Space

To prevent further adverse effects brought about by moisture in your home, you need to reach the acceptable crawl space moisture levels. The US Environmental Protection Agency (EPA) noted that relative humidity in a building should be between 30% and 50%. Low humidity may also prevent dust mites and pests from thriving at home.
In most cases, crawl space moisture levels rise due to steam radiators, humidifiers, combustion appliances like stoves, and moisture-generating appliances, such as dryers.

How to Get Rid of Moisture in Crawl Space

If you’re ready to hear the answers to questions about moisture in crawl space how to fix them, here are some crawl space moisture solutions to consider:

  • Dehumidifier. This moisture crawl space fix does what its name says – remove humidity from the air. As a result, it prevents condensation from adding moisture to the crawl space foundation and reduce the relative humidity in this corner of the house.
  • Sump pumps. These are mainly used to remove and change the direction of the water away from the building. They get to work when the water level rises, preventing water from getting accumulated close to your property.
  • Drainage systems. They prevent crawl space moisture problems by carrying water away from risky areas, passing water through the drainage pipe and into a safer area where moisture cannot build up. These are often installed under the gravel.
  • Downspouts. These work just like the drainage systems, but they are used to carry water away from your roof.
  • Open windows. This is ideal in the fall and spring for better humidity regulation in your home. This allows stagnant air to get out and fresh air to get in while maintaining humidity at an acceptable level.
  • Plants. Cactus plants, for instance, are great at seeping moisture from the air or the ground. You may also try ferns. You can put these plants at a certain corner in the house and see them grow even without getting a lot of exposure to the sun.
  • Encapsulation. This can be done by installing vapor barriers to the crawl space’s foundation walls and floor. This also involves sealing all plumbing and supports, as well as applying caulking to the wall and barriers to avoid releasing moisture into this particular spot in the house.
  • Vapor barriers. These are polyethylene sheets that can be placed on the uncovered soil in your crawl space to prevent moisture from seeping through and increasing the relative humidity in the area. They are well-known answers to the question about how to get rid of moisture under the house and you can try installing them in yours, too.

How to Install Crawl Space Moisture Barrier

You can remove a great amount of moisture from your house first by sealing off any source of unwanted moisture from your crawl space using an effective moisture barrier. Just follow these steps:

  • Locate the crawl space entrance.
    This is often found in a closet, as signified by a hatch door, or under the carpet, with seams on them. It may also be found in the pantry, guest bedroom closet, or utility room. In some houses, the crawl space entrance may be found outside the home, close to the exterior walls.
  • Get rid of moisture.
    Use a dehumidifier, large fans, or sump pumps to completely remove moisture and mold from the crawl space. It may take a few days to do this.
  • Clean up the crawl space.
    Given how the moisture barrier is made up of a lightweight, polyethylene material, it is vulnerable to anything that can pierce it. Once any part of it gets pierced, it won’t be able to completely seal the crawl space and prevent moisture from getting in, rendering it useless. Make sure to remove any debris from the area and even out sharp surfaces before laying down the moisture barrier.
  • Lay down the plastic barrier.
    Install the 6-millimeter moisture barrier by rolling it out on the floor, starting from one end and working your way to the other end. Leave some overlap and secure them to the floor with a poly PVC tape. Seal it properly to avoid moisture from getting in.
  • Install barrier to the walls and columns.
    Even the walls should be sealed off. Secure the sheet with double-sided tape. Make sure every single wall space is covered. The same goes for columns in the crawl space that are supporting the weight of the entire house. Cover them up to 12 inches from the ground. Again, use double-sided tape to secure them to the columns and a poly PVC tape to secure the overlaps between the sheets.
  • Cover the vents.
    The vents may have been installed to let stale air out, but this is not exactly the case during summer when moisture build up increases. Aside from the double-sided tape, you may also want to caulk the vents’ edges for an additional layer of protection against moisture.

A moisture barrier can help reduce moisture buildup and the relative humidity in your home if the source comes from below the crawl space, but it won’t work if the problem is from above the area. If you want your barrier to work, don’t forget to address the plumbing and drainage issues around the house. Do it before the water gets into your crawl space and cause more moisture-related problems.

Related Resources:

Conditioned Crawl Space