How To Seal Crawl Space Vents

How To Seal Crawl Space Vents

Are you tired of that unidentifiable, funky smell wafting from your floors coupled with the scratching noises of intruding four-legged guests from below? What about that nagging feeling that no matter what you do, you can’t seem to cool or heat your home to the desired temperature? If the answer to these questions is a resounding yes, then sealing your crawl space is exactly what you should do.

When it comes to the question of how to seal crawl space vents, a clean and sealed crawled space with an excellent performing vapor barrier can effectively eliminate odors by impeding the growth of mold, restricting entry to insects and rodents, and elevating the quality of air. As a result, that eases the latent load on your HVAC system, stepping up its efficiency by a few notches. The resulting encapsulated crawl space also facilitates extra room for storage beneath your home.

This guide will give you insight into how to properly encapsulate or seal a crawl space vent.

Tools Required

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  • Work gloves
  • Trash bags
  • Marker
  • Measuring tape
  • Utility Knife
  • Knee pads
  • Drill with masonry bits
  • Disposable breathing mask
  • Ample lighting: utility lamps, flashlight, or headlamps
  • Rubber paint roller
  • Protective eyewear

Materials Required

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  • Double-sided construction tape
  • Mechanical fasteners such as termination bars
  • Concrete screws
  • Vapor barrier seam tape
  • Vapor retarder or crawl space vapor barrier or moisture barrier


a crawl space vent
Image Source: Devin Holland
  • Duration: Up to 12 hours for two people per 1000 sq. ft.
  • Difficulty Level: Moderate to high depending on the amount of clearance of your crawl space. The tighter the space, the more challenging the project.
  • What it entails: Working, cutting, taping, and drilling in tight spaces.

Step 1: Prepare The Crawl Space

While it might be a challenging part of the process, depending on the age of your home and its previous owners, clean out the crawl space and prepare it for crawl space encapsulation.

Although it’s a no-brainer that your crawl space isn’t where you spend much time, you might discover that a wealth of other living things have found a sanctuary underneath your home that is ideal for eternal rest, acorn storage, or breeding.

The arduous clearing and cleaning of the crawl space will deliver a great wellness check for your home. The preparation process can be done in the steps below.

Avoid Still Water

The last thing you need is electrocution when you bring lighting or power to the crawl space. If you have still or standing water in the area or excess moisture buildup, consult a professional before you enter.

Clear and Clean the Area

Once it’s safe to proceed, get rid of sharp rocks, old poly, debris, and wet/old insulation. Install the crawl space vapor barrier on the ground and get the surface as smooth as possible for optimum comfort and safety while working on the crawl space floor.

Perform a Wellness Check

A wellness check involves calling an electrician to check loose wiring and a plumber to examine the pipes, wood rot, or termite damage. It’s always recommended to engage the professionals now that they have a clear path to eliminate any problem areas.

Air Conditioning

Determine how the crawl space ventilation works. Whether you require a dehumidifier and other items in the space can determine where and how you locate your drainage and insulation.

Step 2: Get Started With The Walls

With a clear and clean crawl space, it’s time to start by addressing the vertical surfaces. The wall liner that’ll be in a fixed position will eventually tie into the horizontal plane. Therefore, the foundation walls are the most ideal place to get started. Ensure excess material from your wall liner that ties into the horizontal cover overlaps with the ground vapor barrier at 6-inches.

Keep in mind that you should leave a small gap at the top of your masonry walls to remain in compliance with your local building codes. If the code doesn’t indicate the exact size of the gap to leave, leave 3 to 4 inches exposed for a termite inspector to get the job done.

  • Begin by applying the double-sided construction tape to the masonry wall
  • The adhesive backing of the tape will effectively hold your installation firmly in position until you can permanently secure it with a mechanical far, for instance, a termination bar
  • Slowly remove one side of the release liner, moving gradually along the wall while pressing the adhesive down firmly to form a straight line
  • Apply the unrolled vapor barrier along the vertical wall to the double-sided, exposed tape. Keep in mind that the tape serves as the sealing to your crawl space, barring harmful odors and moisture buildup. Therefore, apply it uniformly and firmly around your masonry walls
  • Ensure the vapor barrier extends higher than the double-sided tape
  • Once the vapor barrier is stuck to the walls, use the concrete with termination bars to secure it firmly in place
  • Most masonry screws call for pre-drilling a hole into the concrete wall. If the termination bar has holes to hit, position the term bar as a template to mark them

Step 3: Penetrations And Pipes

Before you roll out the vapor barrier in your crawl space, keep in mind that the most efficient way to encapsulate your crawl space is to first address the fixed position areas. Therefore, that holds for utility penetrations such as pipes that pass underground and into your house.

It’s advisable to handle these tricky spots with small patches of material to cut down on the effort and time of rolling out material in these areas.

Then, use seaming tape to hold everything in place. Remember that the complete installation will result in a monolithic seal of the crawl space from soil gases and vapor. That includes the pipes and penetrations to tightly seal the vapor barrier around each pipe or penetration using the seam tape.

Step 4: Columns

If the crawl space includes columns, particularly masonry, then preparing the columns is the next course of action. Here’s how to get the ball rolling.

  • Use double-sided construction tape to prepare the columns just as you would the foundation walls
  • Then, use the same smaller and lightweight vapor barrier that you used on the termination bars and vertical walls

Although the foundation walls have an adequate vapor barrier to lay flat on the ground, the extra material can make the columns trickier. At every corner of the column, cut a relief slit into the material for it to lay flat.

Doing so will facilitate a four-edged, tight encapsulation of the column while availing an excellent seaming target that will come in handy when you roll out the material on the ground.

Step 5: Roll Out

If you’ve followed these steps to the letter, that’s your cue to roll out the vapor barrier to entirely cover the crawl space surface. Whether you’re running up against detail work such as your walls or overlapping three seams of material, remember to overlap each seam by at least 6 inches.

Once you tape down all the seams, you’re good to go. As a tip, some manufacturers have wider roll dimensions to save you the materials, time, and effort compared to using seaming tape.


With these steps, you’ll be well on your way to converting your dank crawl space, taking care of any moisture problem you have, getting rid of the critters lurking in it, and eliminating odor, turning it into a healthier environment that will benefit your home in its entirety. An encapsulated crawl space will work magic on your indoor air quality, energy efficiency, and pest control.