How To Encapsulate a Crawl Space: (9 Step DIY Guide)

The importance of ensuring that the crawl space is dry is a lesson I see many people learn the expensive way. Unfortunately, they don’t realize that the crawl space is wet until it’s too late. While homes can look pristine from above, the area below the floors could be dank and wet.

Over time fungi and molds could start proliferating beneath your floorboards which won’t only weaken the beams but will also affect the air quality inside your house. Add to that a few critters like rats that may not like to share your new home with, and you will quickly realize that it is critical to ensure that the crawlspace beneath your home is completely dry and sealed.

Fortunately, if the damage from moisture is minimal, encapsulating the crawl space under your home can be undertaken as a DIY activity.

 Encapsulating a crawlspace involves the following:

  • Covering the dirt floor so that any moisture in the ground cannot rise into your floorboards
  • Insulating the sidewalls
  • Sealing off any vents or openings to the outside where moisture could enter from outside
  • Installing a dehumidifier to keep the air below your home dry.

Benefits of Encapsulating Crawl Spaces?

By encapsulating the crawl space, you can prevent moisture from rising and coming into contact with your home’s wooden frames and flooring. Moisture and dampness cause rot which weakens the structure. In addition, mildew and mold form spores which can negatively affect the air quality inside your house.

Encapsulating the crawl space under your home will also keep damage-causing termites out.  Wood-eating termites can enter your home without you being aware that they are there and can cause a tremendous amount of damage to the structure of your house.

An added benefit for sealing off the crawl space is that you will see significant energy savings. By covering the soil under your home, you are essentially insulating the rest of the house from being directly in contact with the cold later of earth on which it lies.

Let’s Get Started!

Step 1 – Perform a Thorough Inspection

The area below your house can be pretty scary. It’s often cold, dank, and dark, with bits of old building rubble lying about. From your inspection, you need to take note of what you need to correct to repair the damage that may have already happened and have a clear picture of the layout before you begin the process of encapsulating the area.

Things to look out for when doing the initial inspection:

  1. Look for water seeping into the crawl space

If yes, check your guttering and grading around the house. Encapsulating the crawl space won’t be effective if groundwater is seeping in under your home. Keep all season’s weather in mind while doing this – do your inspection based on the rainiest season.  

  1. Check for damage to the wooden beams and joists

If there is any sign of rot in the floor beams, you will first need to replace all damaged sections before continuing.

  1. Check for signs of mold

Using a flashlight, check for any signs of mold or mildew. Inspect the corners and areas where rafters are joined. If there are any signs of decay or mold, this needs to be thoroughly treated and all signs of mold removed before starting the encapsulation process.

You can clean mildew that you see by spraying it with foaming mildew killing spray or soaking it in a chemical specially formulated to kill mold. The most important thing that you must remember is to clean and fully dry the areas you have treated for mold before starting the encapsulating process.

Sweep up and remove any debris that has fallen while you were cleaning.   Consider backing up any spot mildew treatments that you have done with a fogger to ensure that there is no chance that any spores could start growing again.

A product like DWD2 Home and Commercial Mold Treatment would be perfect. An aerosol of this kind has been developed specifically to kill all microscopic and airborne spores that may still be circulating.  

  1. Carefully inspect areas where your gas appliances backdraft

Once you have encapsulated your crawl space, the last thing you want is for toxic fumes from some of your gas appliances to possibly be venting into a sealed area.  This could result in a hazardous situation if the fumes build up too much.

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Why Home Inspections Are Important
  1. Level out the ground as much as possible and note areas you will need access to in the future

During your inspection, remove any bricks, rubble, or old beams left lying about during the construction of the house. 

Keep a special lookout for sharp objects like nails or bits of metal that could later puncture the vapor barrier. If the area is neat and level, the process of covering the ground will be much easier.

  1. Measure the surface area and the height of the walls

Since you are already down there, take your tape measure along and note the size of the area you will need to cover.  You should mark special requirements like specific areas of plumbing and wiring that will need to while encapsulating the area.  

Step 2: Seal the Area off From the Outdoors

Older buildings, in particular, may have several vents. Some were even decorative from the outside. The intention was that, theoretically, the air was supposed to allow unrestricted airflow beneath the structure. This isn’t particularly effective, especially in humid climates.

These are also places where critters and bugs can enter and thrive below your home. I once had to call the bee removal guys to come and relocate a swarm that had built a hive in the crawlspace, and it was not easy to get them out safely.

Seal all openings to the outside. You can use foam board and foam spray to completely close all gaps. An excellent way to identify small gaps is to work on a sunny day, and while you are inside, switch off your torch and see where sunlight is coming in.

Your goal is to create an encapsulated sterile pillow for the building to rest on, so all holes need to be adequately sealed.

Step 3: Add a Thermal Barrier to Your Walls

By adding a thermal barrier to your walls, you can keep the temperature inside the crawl space from fluctuating dramatically through the seasons. The result will be savings on your heating and cooling bills, so it is worth considering.

Foam insulation board can either be used around the outside walls of the crawl space or just in areas of particular concern, for example, if your house is sea-facing or experiences regular heavy weather from one specific direction.

Step 4: Decide on the Thickness of the Vapor Barrier You’ll Need

There are various thicknesses of vapor barrier plastic available—these range from the thinnest, which is 6 mil, to the thickest, which is 20mil. The thicker the plastic, the less likely it is to puncture and will last for longer. If you use your crawl space to store anything, it may be worthwhile to invest in reinforced plastic.

The other important factor you should consider when deciding on the thickness of the vapor barrier that will be right for your home is inspecting the ground in the crawl space. If it consists entirely of bare dirt, you may want to consider a thicker reinforced plastic covering. 

Step 5: Calculate How Much Vapor Barrier You’ll Need

When calculating the area you need to cover, don’t forget to purchase enough material to overlap at each seam. You need to work out the amount required to cover the entire floor area and the walls.  The amount overlap should be at least 6-12 inches at each seam.

Step 6: Tape the Seams to Seal the Barrier

It is vital that the vapor barrier material sticks properly to the top of the inside wall and that there are no gaps. Generally, you will need a lot more tape than you think! Remember that you may want to wrap a few strips around the top of piers or towers to ensure that no moisture can get into the area.

There are a few different types of tapes and fasteners that you may need for various sections while securing the vapor barrier.

  • Vapor Tape – this is the standard type of tape used that seals and waterproofs.
  • Butyl Tape – for more challenging areas, this specifically designed tape will hold the liner as you move along, applying it to the sides. This tape can also be used in the areas where the liner overlaps as it is double-sided. While you are working, the seams won’t pull apart, and you can use the regular vapor tape later to tape down the loose top edges later so you won’t hook up when you come down there later. 
  • Christmas Tree Fasteners – these are also called ratchet fasteners and are used to secure softer materials to solid objects. By drilling through the Butyl tape at regular intervals, you can create an airtight, secure seal.

Step 7: Install a Dehumidifier

If your crawl space never had a damp problem, there is no need to fit a specific dehumidifier. You should just regularly check that the area is still dry, and if necessary, you can just run a line and use your normal dehumidifier for a few hours. You could even run an electric fan for a few days until you are sure that your crawl space is entirely free of any dampness.

If you have struggled with damp issues in the past, it may be a good idea to fit a commercial-grade dehumidifier specially designed for this area. Crawl space dehumidifiers differ from regular units because they are small enough to fit into the area and drain directly to the outdoors.

I recommend the Santa Fe Compact70 Dehumidifier available at Amazon. I’ve seen many of these over the years, and they do a great job. Don’t try to use an indoor dehumidifier in a crawl space, as the collection bin fills quickly and will shut off if not emptied.

You’ll also need a condensate pump to expel the water collected to the outside. I recommend the Little Giant Automatic Condensate Removal Pump with Safety Switch available at Amazon.

You’ll need a GFCI protected outlet to plug in the dehumidifier and condensate pump in the crawl space. You should call an electrician to install an outlet protected by a GFCI breaker. You should do this so that if the GFCI trips, you can easily reset it without going into the crawl space.

Both the dehumidifier and condensate pump are available below:

Step 8: Don’t Forget the Access Door

Before you finish, don’t forget to put sealing insulation tape around the edges of the access door that leads down to the crawl space. The door was probably open while you were working, so before you leave, be sure that there are no gaps around the frame where moisture could get in.

Step 9: Do Regular Inspections of the Crawl Space

After completing this task, the only thing left to do is to routinely do checks that everything is still as you left it. Over time, tree roots or burrowing rodents could break the barrier seal over the floor, so an occasional look around is well worth the effort. The most critical time when this check should perform is before the onset of winter.  Any rips in the vapor lining would allow the air in the space to cool, which will lower the temperature in your house.

Conclusion

The crawl space under your home does not have to be a damp and musty space that is full of cobwebs. By encapsulating the area, you can create an insulated pillow under the floor of your home that will protect your wooden structure from rotting and ultimately save you money on energy bills.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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