Should You Put Plastic Under Your House in the Crawl Space?

Plastic sheeting in your crawl space can serve a number of useful purposes. Primarily, plastic is installed in crawl spaces to residential buildings to create a barrier against moisture or vapor. This approach helps minimize the risk of mold or mildew intrusion into the home. It can also help create a more suitable storage space for homeowners. It's important to choose the right kind of plastic sheeting for both of these purposes, and to install it correctly.

Under the Porch
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Should You Put Plastic Under Your House in the Crawl Space?

Why Install Plastic in Your Crawl Space

Homeowners use plastic to cover their crawl spaces to control moisture and create a barrier against vapor. Without such a barrier, condensation can infiltrate your home's walls and insulation, creating a substantial risk of mold and mildew. Plastic sheeting can also help turn a crawl space into a usable storage area. A sheet of plastic will help keep properly stored items dry and free from soil and insect intrusion.

Materials You’ll Need

To install plastic in a crawl space, you'll need a straightedge, tape measure, landscape fabric stakes, hammer, utility knife and duct tape.

Bear in mind regional climate and soil differences can call for variations in materials and approaches. However, for most homeowners sheeting made of polyethylene plastic is the best choice for moisture abatement and storage protection.

While some sources may recommend a thickness of six-mil, a thicker grade of material is preferable. Thinner sheeting may be more pliable but generally is not sufficient as a barrier against vapor or moisture.

Additionally, six-mil sheeting can easily be damaged during other crawl space work, including pouring concrete or reinforcing supports. This can create larger holes in the plastic that allow moisture to seep through, defeating the purpose.

Instead, experts recommend sheeting that's either 10-mil or 20-mil for enhanced durability and moisture resistance.

Measure your crawl space's length and width before purchasing your plastic sheeting to make sure you're buying a sufficient quantity. The plastic sheeting you'll need can range from 6' to 30' in width, and come in rolls up to 200' long.

How to Install Your Plastic Sheeting

With your sheeting and materials assembled, begin to cut and lay down strips of your plastic sheeting over the open soil area in your crawl space. Make sure seams between your plastic sheets overlap each other, then tape them down.

Use the landscape fabric stakes and hammer them down into the soil around the edges to secure the sheeting to the soil. Additionally, at the edges of your crawl space where the soil meets the walls, leave several inches of sheeting allowance. Masonry foundation walls should be covered either with moisture-proof insulation or drywall.

A Word About Radon Mitigation

Radon is a colorless, odorless radioactive gas that at certain levels over time will increase the risk of lung cancer. Radon is naturally occurring from igneous rock, soil and some wells, though it's usually the underlying soil in your crawl space that will pose the biggest potential risk to your home and its occupants.

You may want to consider installing plastic sheeting in your crawl space as part of an effort to mitigate radon. Plastic sheeting can help protect your home and occupants from radon infiltration if properly installed.

However, you'll want to seek out a professional for this purpose. Given the seriousness and significance of the potential risk, it's wise to leave radon mitigation as a whole to an experienced contractor who can tackle the entire job for you.