Do You Need Vapor Barriers in Your Crawlspace?

Moisture seeping into your home's crawlspace can cause problems ranging from structural damage to mildew and bacteria buildup. Keeping your home's interior safe can be as simple as installing a crawlspace vapor barrier that controls moisture and keeps the area clean and dry.

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What Are Crawlspace Vapor Barriers?

A crawlspace moisture barrier is made of thick polyethylene plastic sheeting and designed to cover the sides and floor of your crawlspace. Moisture can come from condensation and ground seepage, which is why both the floors and sides require coverage. Vapor barriers control moisture but aren't completely waterproof, so they can't keep out floodwater.

The crawlspace vapor barrier material should be thick enough to sufficiently keep out moisture and resist punctures. For extremely damp environments, you might also want a drain system that funnels water away from the area and a dehumidifier that pulls moisture from the air.

What Does a Vapor Barrier Do?

Crawlspace vapor barriers, also known as vapor retarders, block out moisture that could cause damage to your home. This moisture comes into your crawlspace from the surrounding ground and can cause problems if left unattended.

Some of the potential problems caused by ground moisture in a crawlspace include:

• Damage to electrical wires or connections in the space

• Structural damage due to rot

• A buildup of mold, mildew and allergens

• Rusting of pipes in the crawlspace

• Degradation of crawlspace insulation

Vapor barriers also improve indoor air quality. Because the air in your crawlspace sometimes travels up through the floor into your home, a properly installed vapor barrier reduces exposure to potential contaminants, such as mildew and mold.

Do Vapor Barriers Work in a Crawlspace?

A vapor barrier under the house or in a crawlspace blocks out humidity and small amounts of water vapor, but it doesn't block flooding or pooled water. Vapor barriers should only be installed in a dry crawlspace. If the wood or concrete in your crawlspace is already wet, installing a vapor barrier over the damp areas could trap moisture and lead to further damage.

Vapor barrier installation in a home crawlspace can be a DIY project, but it's often a good idea to hire someone to install the plastic liner. Before putting crawlspace plastic down, you need to make sure the area is clear of debris and graded so the floor surface is level. During installation, you need to ensure the plastic sheets overlap and the seals are airtight between them. Exposed dirt or wall surfaces could let moisture in later, so you want to aim for full ground coverage. An annual inspection to check for rips and holes helps keep a crawlspace vapor barrier working effectively for up to 20 years.

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Do You Need Vapor Barriers in Your Crawlspace?

If your area is prone to moisture or humidity, it's a good idea to have a crawlspace liner that keeps things dry. An under-home vapor barrier can also keep out pests, including insects and rodents. Crawlspaces with a dirt floor often need a vapor barrier to prevent seepage from the ground.

Some local building codes may require the use of a crawlspace vapor barrier. In this case, there may also be requirements for the minimum thickness and the type of material used. The cost of a vapor barrier depends on the exact material used and the size of the crawlspace.

Overall, crawlspace vapor barriers provide protection from moisture and are a good investment in areas with heavy humidity or groundwater seepage. Keeping the crawlspace dry can help prevent costly structural problems and improve the air quality in your home.