Crawl Space Encapsulation: Pros, Cons and Costs

Though it’s a part of the home that you rarely visit, the health of your home’s crawl space can have a serious impact on the entire house. A damp crawl space can lead to mold growth that can have serious impacts on indoor air quality. It can also cause wood rot that can damage the framing around the home’s foundation.

A crawl space can also attract pests such as insects, rats, and even snakes. Fortunately, there’s a solution for homes that face these challenges: crawl space encapsulation. Crawl space encapsulation seals the crawl space of a home with thick plastic sheeting and maintains the humidity level in the space with a dehumidifier, eliminating excess moisture while keeping pests out. 

In this article, we’ll explore the pros and cons of encapsulating your crawl space, what you can expect to pay for a project, and review the steps that encapsulation involves.

Crawl Space Encapsulation

What Is Crawl Space Encapsulation?

Crawl space encapsulation involves sealing off the crawl space under a home using plastic sheeting to create a clean, dry area that prevents mold growth while keeping pests out. While a basic encapsulation may only involve installing plastic sheeting, more sophisticated encapsulation projects might also require the addition of a dehumidifier to maintain the humidity level in the space and a drainage system to prevent water from collecting under the house.

Should I Encapsulate My Crawl Space?

Whether or not one should encapsulate their crawl space is largely a question of whether the benefits justify the cost, which can be considerable.

Given that the average cost of a crawl space encapsulation is $5,500, it only makes sense to encapsulate a crawl space if it’s going to pay off by protecting one’s home. If your crawl space remains dry throughout the year and is pest-free, it may not make sense to invest the money in encapsulating it.

However, if you have a crawl space susceptible to mold growth or routinely attracts pests, encapsulating a crawl space may be worth it when one considers all the headaches a crawl space can cause.

These tight areas with limited airflow can be a haven for mold, which, when unchecked, can do structural damage to a home while lowering the indoor air quality in the living area above.

Encapsulate crawl space diy
Crawl Space. Source: avlxyz

Pests can wreak havoc on a home’s foundation or use the crawl space as a means for entering the home’s living areas. Once they’ve infested a home, removing them and repairing any damage they’ve created can be a costly endeavor.

A damp crawl space will also cause wood fibers to deteriorate faster, eventually resulting in rot to the framing around the first level floor, which can be very expensive to correct.

If encapsulating your crawl space is something you’re considering, then you more than likely are dealing with one or more of the above problems. Given the amount of damage these issues can cause, it may make sense to protect your investment by springing for the cost of encapsulating a crawl space.

Benefits of Crawl Space Encapsulation

Encapsulated crawl space
Crawl space finishing. Source: Greg Marks (1)

There are many benefits to encapsulating your crawl space, ranging from eliminating excess moisture in the space to keeping out dangerous gases that emanate from the earth. In this section, we’ll review the benefits you can expect from a crawl space encapsulation.

1. Reduces Moisture and Mold

While moisture and small puddles of water in a crawl space won’t cause structural damage to your home, they can create conditions that will. The water vapor these puddles produce can cause mold and rot on the walls, weakening the home’s framing. Mold can even take root in wet insulation.

Encapsulating a crawl space of a home located in a region with high humidity will eliminate the moisture that causes these problems.

2. Prevents Pests From Entering the Crawl Space

Water and moisture also attract pests such as rats, termites, spiders, dust mites, and other creatures you don’t want taking up residence under your home. Eliminating moisture in the crawl space makes the habitat under your home less hospitable for rodents, insects, and reptiles.

Plastic sheeting also creates a barrier that keeps creepy crawlies out of the space while making it more difficult for them to find an entrance into the living space of the home.

3. Serves as a Barrier Against Gases, Dust, and Allergens

As much as 50 percent of the air in a home’s living area originates from the crawl space. This means the air quality in a crawl space directly impacts the air quality in your home. Mold spores, dust, and gases released from the earth can find their way into the home, creating a musty smell and exacerbating respiratory problems.

Encapsulating the crawl space can dramatically improve the air quality in the crawl space, translating into much cleaner air in a home’s main living area.

4. Improves Insulation

Most crawl spaces under a home have vents around the foundation that allow air to circulate through the crawls space. While this helps keep a crawl space dry and mold-free, it also allows hot air or cold air to circulate beneath the home.

Given that much of this air finds its way into the living area above, this can make a home’s heating and cooling system work harder to maintain the desired indoor temperature, lowering the energy efficiency of the house.

Encapsulating a crawl space eliminates the need for these vents, which creates a space that is better insulated from extreme temperatures outdoors, improving the energy efficiency of the living space.

When selecting a vapor barrier, consider thicker material that has a higher R-value than thinner cheaper plastic. Though it may be more expensive up front, you’ll make that money back in lower heating and cooling costs.

5. Improve Structural Integrity

Even though there may not be enough moisture in your crawl space to create a mold problem, damp air can still cause the wood framing around the foundation to maintain a high moisture content, which can cause the wood to lose its structural integrity more quickly than dry wood.

This can result in uneven house settling or even more significant structural problems down the road. Damp air in the crawl space can also cause the soil under your home to retain moisture longer. This soft, damp soil can cause different parts of the foundation to sink.

Encapsulating a crawl space eliminates this damp air, keeping your home’s framework and the soil beneath the house dry, improving its structural integrity.

6. A More Pleasant Crawl Space to Visit

Utilities and plumbing typically run under the first floor of the home, which means some household maintenance requires you to occasionally visit the crawl space. It’s a good idea to inspect a crawl space annually to make sure there are no issues with the floor joists or foundation.

You shouldn’t feel like you’re crawling into a musty, dirty space where snakes, insects, and rats may be lurking. A clean, dry space encapsulated in plastic sheeting is a much more pleasant crawlspace to enter than a dank, damp, musty one.

Negatives to Crawl Space Encapsulation

1. Very Expensive

While there are few negatives to encapsulating a crawl space, the biggest hurdle to completing this upgrade is cost. The average cost of encapsulating a crawl space is $5,500, with that price tag jumping to as high as $12,000 depending on the crawl space’s square footage, condition, and the market.

Larger crawl spaces will require more material and time and therefore cost more to encapsulate. Any cracks, mold, moisture, structural issues, or pests that must be dealt with before encapsulating the space will also drive up the cost. The price of a crawl space encapsulation will also be higher in markets in and around major cities with a higher cost of living.

2. Can Hamper Future Maintenance

Most crawl spaces have wires and pumps for the home’s electrical and plumbing running through space. When a home is encapsulated, all of these utilities are typically covered by plastic sheeting.

If there is an issue with this plumbing or electrical, or if you’re making renovations to the above living space that requires access to these utilities, you’ll have to cut away the sheeting to access it then replace it when the renovation or repair is complete, which can be a hassle.

With this in mind, it makes sense to address any maintenance needs before encapsulating the crawl space to limit the number of times you’ll need to cut through the sheeting.

3. Does Not Stop Flooding

While encapsulating a crawl space will keep out smaller amounts of moisture and humid air that can cause condensation, it won’t stop flooding.

If you have a crawl space that periodically floods, you’ll need to install a water drainage system such as a french drain or sump pump that will direct water away from the home’s crawl space and foundation before encapsulating it to prevent water damage.

4. Can Be Tricky With Gas Appliances

If you choose to encapsulate a crawl space and you have gas appliances such as a dryer, water heater, or furnace, it’s crucial to make sure they do not vent into the crawl space.

Gas appliances use combustion to create heat and therefore have carbon dioxide emissions that must vent outside to prevent these gases from building up and entering the living space of the home.

A gas appliance must have a vent that leads outside of the home. Any gas appliances in the crawl space should also be checked by a professional to ensure there are no leaks before encapsulating the space.

How to Encapsulate a Crawl Space Yourself

How to encapsulate a crawl space
Vapor Barrier – Vented Crawlspace Source: The EnergySmart Academy

It is certainly possible to encapsulate a crawl space yourself. And, given the steep cost of hiring someone to do this job, it’s easy to see why you may want to attempt this project on your own. That said, this can be a complicated task that can make a DIYer quickly feel overwhelmed.

In this section, we’ll review the steps this project requires so you can decide if this is a job you’re willing to take on by yourself.

Step 1: Prepare the Crawl Space

Depending on the current condition of your crawl space, this can be an easy task or a challenging one.

Begin by assessing the drainage in our crawl space. If rainwater is draining into the crawl space, you may need to grade around the foundation so that water runs away from home as opposed to toward it. Consider hiring a drainage company to fix these problems before encapsulating the space.

Inspect the floor joists and any HVAC equipment in the home for mold. If you discover any mold, it’s vital that you eliminate these issues before encapsulating the crawl space.

Finally, if you have gas appliances in the crawl space, check to make sure they vent to the outside and are not leaking exhaust fumes or gas. Carbon monoxide emissions and gas leaks are not something you can accurately assess on your own.

Call a professional to assess your gas appliances for emissions leaks and the gas company to ensure no gas leaks. A gas appliance with a minor leak that may not have been a big issue in a vented crawl space can cause a disaster in an air-tight encapsulated space where fumes can quickly build up.

Step 2: Seal the Crawl Space

Encapsulating means sealing off the crawl space from the outdoors.

To do that, you’ll need to begin by sealing any vents in the foundation walls of the crawl space. Cut the foam insulation to fit the vent cavities and seal them in place using spray foam.

Next, look for smaller gaps around the crawl space, including cracks that can allow outdoor air to enter the space and any gaps between vent pipes or wiring that may run through the foundation walls or the above floor sheathing. Seal these cracks and gaps using spray foam insulation.

Step 3: Determine How the Air Will Be Treated

For encapsulation to be effective, you’ll need to maintain a humidity level of around 50% in the crawl space. For that, you’ll need a dehumidifier specially designed for use in crawl spaces. These box-shaped units are about the size of a small cooler and typically run off of a standard 120-volt outlet.

They are typically rated by the amount of square footage they can serve. Place the dehumidifier in a central location in the crawl space so it can effectively serve the entire space The rubber tube that runs out the back of the unit that drains the moisture the dehumidifier condenses out of the air must run to the exterior of the house to an area that drains away from the foundation.

Step 4: Cover the Walls

It’s time to encapsulate your crawl space. Begin encapsulation by covering the walls with plastic sheeting. Starting with the walls first makes it easier to overlap the crawl space vapor barrier later.

Carefully run double-sided construction tape around the masonry that makes up the foundation wall of your home, making sure to leave a gap of about 3 inches between the tape and the wood framing of the house that rests on the foundation. This gap will give the termite inspector access to the framing that’s in the crawl space.

Once the tap is in place, remove the liner to expose the sticky side of the tape. Hang the sheeting by pressing it against the double-sided tape. The sheathing should be wide enough to run onto the floor of the crawl space so that the crawl space vapor barrier can overlap it by at least 6 inches.

Once the sheathing is attached to the tape, secure it in place using a termination bar with masonry screws.

Step 5: Columns and Pipes

Before laying the plastic vapor barrier on the floor, you’ll need to deal with any piers or pipes first. Cut small pieces of sheeting to size secure around any pipes or other utilities that may need to pass through the plastic sheeting. Use seam tape to create a tight fit.

Attach vapor barrier to square peers using the same method you used to secure sheeting to the wall. You’ll need to make cuts to the corners to allow the sheeting to lay flat on the floor around each pier.

Attach double-sided tape to the piers, then run sheeting around the peers and finish with termination bars.

Step 6: Install the Vapor Barrier

Now that the walls are covered and you’ve prepped the space by covering the support piers and any pipes, it’s time to install the plastic vapor barrier.

Unroll the vapor barrier out in space. Make sure to overlap seams on the floor and walls by at least 6 inches and tape each seam with seam tape so it’s secure.

How Much Does Crawl Space Encapsulation Cost?

A homeowner will spend an average of $5,500 to encapsulate a crawl space, according to Home Advisor. This cost includes both supplies and labor. That said, costs can vary widely from $1,500 up to $15,000 depending on various factors.

Some encapsulations are more involved than others. Encapsulation systems that only consist of thin plastic will be much cheaper than those that include thicker materials or multiple vapor barriers. The addition of a crawl space dehumidifier can add between $500 and $1,000 to the cost.

The installation of a crawl space drainage system can add hundreds or thousands of dollars to the cost depending on how complex the system needs to prevent the area from flooding. Other factors that affect total cost include the size of the crawl space as well as the market.

Does Crawl Space Encapsulation Add Value to Home?

Crawl space encapsulation eliminates moisture issues and protects the foundation of your home, so it does add to the value of the house. While the return on investment for encapsulation may not match the amount you put into it, it certainly makes a home more attractive to potential buyers. It also shows that you care about the condition of your home since you’re willing to protect the areas people rarely see, which can impact a potential buyer’s perception of the home.


Though it is a significant investment, encapsulation is an excellent solution for homes that are dealing with moisture or pest problems in the crawl space. Encapsulation creates an air-tight space that will prevent mold growth while keeping insects, rodents, and reptiles out.

It also makes periodic visits for termite and foundation inspections and utility maintenance a more pleasant experience.

While encapsulation is often a big project that is best left to the pros, the high cost of encapsulation installation may prevent this option. By carefully following the steps outlined above, encapsulation is certainly a project one can complete on their own.

Whether hiring a professional to do the job or doing it yourself, make sure to properly prep space by addressing any drainage or pest issues and by inspecting any gas appliances that may be in the crawl space before encapsulating.

(1) Shared under a Creative Commons (BY) license

Written By: Yevgen

YevgenI'm a DIY nut, and the founder and chief editor here at Weekend Builds.
This site is a result of my DIY passion, and to share the joys I have experienced fixing, building, and creating things over the years.

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