How to Seal and Encapsulate a Crawl Space

A pop of color on a front door or an accent wall will surely get you paid compliments, but some DIY projects while not visual, or even visible, pay greater dividends. DIY crawl space encapsulation certainly falls into this category.

No one will know you did it unless you say so, but the benefits go beyond most above-ground projects you attempt. Granted, few homeowners want to spend time in their crawl space, but if you take an "out of sight, out of mind" approach to your crawl space, it could easily become "out of sight, out of pocket."

What Is Crawl Space Encapsulation?

Encapsulating your crawl space is simply insulating the walls, using a vapor barrier on the dirt floor, and sealing off vents and outdoor openings to reduce more humid air entering. Properly sealing your crawl space doesn't take any specialized tools or skills (but you may want to invest in some quality knee pads).

One quick trip to the hardware store for readily available materials and a day or two of your time (depending on the size of your crawl space) and you will soon be reaping the benefits of cleaner air in your home and using less energy to heat and cool it.

What Is a Vapor Barrier?

Pros of DIY Crawl Space Encapsulation

Cost

DIY crawl space encapsulation can cost upwards of a couple hundred dollars, but that is a fraction of the cost of having it done professionally which can be in the neighborhood of $3,000-5,000.

Improved Air Quality

About 50% of the air in your home comes from your crawl space. Encapsulating it will significantly reduce foul or musty smells in your home, potentially reduce allergen and asthma problems by improving the air quality, and can increase HVAC efficiency by up to 20%.

Prevention of Larger More Expensive Repairs

Avoiding sealing a crawl space can result in larger, more costly repairs in the future. Wet, humid crawl spaces left unattended can develop mold, musty smells, and even sagging or rotting joists and subfloors.

Pest Prevention

Crawl space sealing goes a long way in preventing unwanted guests from making your home their home. Rodents, termites, and carpenter ants to name a few find a wet, humid space the perfect accommodations to live, breed, and compromise your home's foundation.

Potential for Increased Storage

Depending on the size, ease of access, and the degree you can keep water and humidity out of the crawl space, you may find it an ideal location for seasonal or long-term storage.

Cons of Crawl Space Encapsulation

Discovering Unforeseen Problems

Applying a vapor barrier is a fairly straightforward project, within the capabilities of many DIYers. However, discovering pest infiltration, wood rot, a faulty sump pump or an extremely unlevel crawl space floor may push this project from DIY to needing to consult professionals.

Potential HVAC Upgrade

Encapsulating a crawl space increases the energy efficiency of your home, which can reduce the amount of air movement. This could result in older furnace units needing to work harder (perhaps too hard) to maintain a comfortable temperature in your home.

Personal Time and Discomfort

Because, by definition, a crawl space usually requires crawling, and because the space is dark, dank, and off-putting, it may just be beyond the discomfort some homeowners are willing to endure to DIY it, even if it is found to be fairly straightforward.

Add in the fact that, depending on the size and condition of your crawl space you may be down there the better part of a few days, it just might not be a project everyone feels like tackling themselves.

Cost/Time to Maintain

Encapsulation of a crawl space doesn't have to be a major financial investment, but it does require some consistent attention and perhaps some financial investment to keep the space from being compromised.

Tools and Materials

Spray Foam

There is a wide variety of foams on the market. Some are designed to fill big gaps, others for narrow cracks, and some are specially formulated for insect control. You also have the choice of brands that are latex which makes clean-up easier.

Weather Stripping

Many varieties of weather stripping are available for various purposes, particularly for access doors and vents.

Measuring Tape

To accurately determine how much vapor barrier and other materials you'll need.

Flashlight or Head Lamp

Of course for seeing better (it wouldn't hurt to have a backup just in case).

Caulk

For filling cracks and smaller gaps.

Scissors or Utility Knife

For cutting vapor barrier, waterproof tape, and insulation.

Insulation

Fiberglass batting is helpful for nooks and crannies and between floor joists. Rigid foam board is great for larger areas and the inside of access panels and doors. Foam board should be at least two inches thick with an R-Value of at least 10.

Plastic Sheeting (Vapor Barrier)

The minimum thickness recommended by experts is six millimeters (the thicker the better).

Waterproof Tape

To seal seams and around cuts and openings in the vapor barrier.

Rake and Shovel

May be necessary if the crawl space is not level enough for efficient vapor barrier insulation.

Gloves and Kneepads

It is, after all, a space for crawling.

Clothing You Don't Care About

This is not the time to wear a coveted concert shirt or your 'good' anything.

Before You Begin Crawl Space Sealing

Ensure Proper Grading

Take a walk around the outside of your home and make sure you have proper grading.

Soil, mulch, landscaping, and lawn should slope away from your home's foundation. If it doesn't, you're definitely going to want to address that sooner rather than later.

Study Your Home’s Floor Plan

If you happen to have a copy of your home's floor plan handy, a quick study of it can help you more readily navigate what's down there, make the process more efficient, and help you estimate how much you'll need of various materials like plastic sheeting and insulation.

Gather and organize tools and materials and help. Before you head down there, create a checklist of tools and materials as well as a convenient method to transport them (a bucket or milk crate works well—tool belts can be cumbersome in such tight spaces).

Of course, it never hurts to have an extra set of hands to make the project go more smoothly and quickly, but this can be a one-person job. If you will be doing this solo a charged smartphone is quite helpful should you need to contact someone above for materials, tools, assistance, or even a snack.

It's also handy to take photos you may need to assist you with any potential issues that you may not be able to identify yourself in the moment, and for future comparison of the condition of your crawl space. Plus, it's a bonus flashlight.

Inspect Your Crawl Space

Before any encapsulation begins, you will want to inspect your crawl space for rot in your beams, joists, subflooring, and any other supportive wood. You will also want to look for, and eradicate, any mold or fungus.

Not doing so will result in the mold or fungus being trapped in place, essentially defeating the purpose of the encapsulation. Remove and locate the source of any standing water and check that your sump pump is functioning properly.

This is also the best time to look for and eliminate any signs of unwanted 'guests' that could have been calling it home and will want to do so again for themselves and their offspring.

Sealing Your Crawl Space

1. Remove Existing Vapor Barrier

If your crawl space already has a vapor barrier, remove and dispose of it.

2. Inspect the Crawl Space Floor

If the floor of the crawl space looks relatively level, you can comfortably proceed with installation. However if there are obvious hills and dips in your floor you may want to take steps to even them out preventing water from pooling.

3. Cut and Install the New Vapor Barrier

Again, experts recommend at least 6 mil thick plastic sheeting for crawl space floor and walls (the thicker the better). Be sure to overlap sheeting by at least 6 inches to ensure moisture is kept out. For an extra level of protection, seal the seams with waterproof tape..

4. Cover Foundation Piers, Pipes, Wires, and Plumbing

Make tight, close cuts and use waterproof tape to seal any seams or cuts. You can also use plastic sheeting on crawl space walls, but rigid foam insulation is easy to handle, easy to cut to size, and easy to install on walls and between subfloor joists.

Fiberglass batts can also be used to insulate between subfloor joists and smaller gaps.

Sealing Vents, Crawl Space Access, and Gaps

1. Vents should be completely sealed and caulked. Rigid foam insulation (preferably at least two inches thick or with an R-value of at least 10) works well in this application.

2. Access panels/doors to the crawl space should also have rigid foam insulation applied (again at least two inches thick or an R-value of at least 10). But because these panels/doors will be opened and closed, use a high quality weather stripping to get a tight fit that will seal out moisture.

3. Cracks and gaps should be filled with expanding foam or caulk. Ignoring these small openings can be enough to defeat the purpose of encapsulating your crawl space.

After You've Encapsulated Your Crawl Space

Now that you know the steps to successfully sealing your crawl space, you're going to want to consider protecting your (money and time) investment. The best way you can do this is to make sure the space remains dry.

Consider purchasing a crawl space dehumidifier. A dehumidifier specifically designed for crawl space use does so much more work than a household dehumidifier is capable of tackling.

Encapsulating a crawl space goes a long way to keeping moisture out, but a dehumidifier conditions and pulls moisture out of the crawl space air depositing it in your sump pump pit (or outdoors if you don't have a sump pump).

The downside to adding a dehumidifier to your encapsulation project is the cost. The unit, alone will range from 300-1200 dollars depending on the model and size, and expect to add another $1000 for labor and installation. This is a project not many DIYers would want to tackle themselves.

If the dehumidifier option is outside your budget, at least consider a humidity monitor ($12-$20). This is a wireless device with a home base that will allow you to keep tabs on the moisture levels and know just how well the encapsulation is doing its job or if there are points of entry for moisture that need to be addressed further.

Just because you've successfully finished the sealing of your crawl space doesn't mean you're forever off the hook for going back down there. You will still want to regularly visually inspect the area for any breaches in the vapor barrier or insulation, particularly if you intend to use your crawl space for storage. Consistent inspections and a humidity monitor can give you some serious peace of mind.

We've laid out the major pros and cons of DIY crawl space sealing for you. The first step for you should probably be to make your own list of pros in cons factoring in how comfortable and confident you are working on a dank, dirty, cramped, and cumbersome project yourself versus having it handled by professionals.

We've already mentioned several worthwhile benefits like improved air quality, higher efficiency for your HVAC system, and vast reduction in potential pests gaining access to your home. But again, there is also cost to consider.

A capable DIYer can successfully encapsulate a crawl space for a fraction of the cost of professionals. We're talking a difference of a few hundred dollars to do it yourself, versus thousands for a pro.

The discomfort you may feel while in your crawl space for a day or two may well outweigh the potential discomfort in your bank account.