A Step-by-Step Approach to Installing a Crawl Space Vapor Barrier

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Any house or building is only as great as its foundation. The tallest of structures wouldn’t even be towering so high if they weren’t efficiently built from the ground up.

That’s why we give importance to crawl spaces, as they could determine how sturdy our structures can be. Now the question is, how do we make sure our crawl spaces can effectively support and protect the rest of the house or building?

While they may seem like tiny threats, moisture and mold go hand in hand in eating away at a structure’s durability. Since crawl spaces invite humidity from the ground, vapor barriers can help keep moisture and mold out.

If you’re looking for ways how to install vapor barriers in crawl spaces, you’re in the right place. Let’s get our hard hats on and dive right in!

What Are Vapor Barriers?

Vapor barriers serve as a layer of protection for buildings and structures against moisture. When a surface gets too exposed to moisture, it becomes an easy target for mold.

Mold can cause some serious damage to buildings and structures as they feast off of the organic materials on their surfaces. With moisture comes the threat of mold, which is where vapor barriers come in.

Vapor barriers also help combat health problems due to moisture and mold build-up. Mold in damp structures leads to poor indoor air quality and puts people at risk for:

• Respiratory problems and infections.
• Trigger or development of asthma.
• Allergic rhinitis.
• Hypersensitivity pneumonitis.
• Headache and fatigue.

Different Types of Vapor Barriers

There’s a variety of materials that can be used effectively as vapor barriers. Different types of vapor barriers include:

• Exterior grade plywood
• Vapor barrier paint
• Aluminum foil
• Metalized film
• Metal and glass sheets
• Elastomeric coatings
• Polyethylene plastic sheets
• Asphalt-saturated kraft paper

Consider your budget, location’s weather, and purpose in installing a vapor barrier. Thicker vapor barriers will cost more but provide better protection and durability.

Installing a Vapor Barrier in Your Crawl Space

While it’s easier to hire a professional, you can save some money by installing a crawl space vapor barrier by yourself. If you have friends or family members that can help, that would also be great.

Prepare the tools and materials you’ll need before installing a vapor barrier. These are some of the tools and materials you may need for this project:

• A garden rake
• Some trash bags
• A brush, duster, or cobweb remover
• A portable work light
• Double-sided tape (acrylic, butyl, etc.)
• PVC (polyvinyl chloride tape)
• Tape measure
• Straightedge
• Utility knife
• Your choice of vapor barrier

Once you have these ready (and hopefully a team to help you), you can get started with the installation.

Clear Your Crawl Space Floor

Before working on anything in your crawl space, it’s best to tidy up first. Doing so will allow you to move and work freely while removing any object that could get in the way of the vapor barrier installation.

Using a garden rake, remove any trash, debris, or sharp objects from the floor of your crawl space. Sharp objects may become a cause of hazard for injury and damage your vapor barrier.

Gather the clutter in trash bags for easy disposal. If needed, try to dry out your crawl space, as you might have a hard time working on wet surfaces.

Take note that if your crawl space is pretty damp, it may take a few days to dry completely. Remove wet materials and set up fans or dehumidifiers at your discretion.

Assess and Measure Your Crawl Space

Take some time to assess the space you’re working with and measure the surfaces of your crawl space. This will give you an idea of how much vapor barrier you’re going to need to cover everything.

To calculate your crawl space’s perimeter and wall and floor square footage, you’ll need to measure the following:

• The longest wall in your crawl space will serve as its length.
• The shorter wall in your crawl space will serve as its width.
• The height of the walls from your crawl space’s floor to its ceiling.

Once you have those measurements, use these equations for reference:

• (Length + width) x 2 = your crawl space’s perimeter.
• Perimeter x height = your crawl space’s wall square footage.
• Length x width = your crawl space’s floor square footage.

Don’t forget to measure any beams or columns since those need some covering too. If you could go through the trouble of sketching a miniature map of your crawl space, that would be very beneficial.

Lay Down Your Vapor Barrier And Start Cutting

Find a large open area to lay down your vapor barrier so that you can cut and section them properly. Don’t try doing it in your crawl space, as you may not have enough space to move around comfortably.

Remember to use your measurements when cutting the vapor barrier. Also, leave at least 6 to 12 inches of overlap in your vapor barrier for allowance.

You can label each section of the vapor barrier you cut for easier installation. Doing so will help you quickly determine where to place them in your crawl space.

Save any excess sheets of vapor barrier from cutting. You can use those later for covering exposed surfaces, columns, and reinforcing seams.

Cover Every Corner, Wall, and Pier

Brush off any excess dust on the wall or surface before applying your vapor barrier. This will help your tape and vapor barrier stick better on its surface.

Covering Walls

1. Apply a generous amount of double-sided tape on strategic spots to your crawl space’s walls.
2. Attach your vapor barrier according to its label and which section it should go in your crawl space. Make sure it runs a tight fit against the surface with no space or room to breathe.
3. Use PVC tape to seal the edges of your vapor barrier against the wall.

Covering Floors

1. Lay down sections of the vapor barrier you cut based on your crawl space’s measurements.
2. Cut extra sections of the vapor barrier to fit the edges and corners of the walls, as well as any piers or columns.
3. Let the overlaps of the sheets you cut run up on the walls and piers. Seal them against the wall with PVC tape.
4. Cover any exposed floor area with excess sheets and seal with PVC tape. Do the same for seams caused by overlaps.

Covering Piers

1. Wrap a tight fit around each side of the pier. If it helps, imagine you’re wrapping a Christmas present in the form of a giant pier.
2. Cut the overlaps of the vapor barrier according to the measurement of each side of the pier. The vapor barrier won’t wrap around the pier tightly if you don’t cut the gaps at the bottom.
3. Seal the top edges of the vapor barrier against the pier with PVC tape.
4. Be sure to cover any seams or exposed areas with PVC tape and excess vapor barrier sheets if necessary.

What Vapor Barrier Size Should You Use in Your Crawl Space?

The amount of vapor barrier you need to use depends on your crawl space’s measurement. Always remember that whatever the results of the measurements are, you need to add 6 to 12 inches of overlap for allowance.

The ideal minimum for vapor barrier thickness is six mils. Though, you’ll need to consider the landscape and purpose of your crawl space.

A vapor barrier that’s at least 12 mils thick or more is best if:

• The floor of your crawl space isn’t smooth and has some natural chunks, such as roots, rocks, and concrete.
• You will regularly access your crawl space for maintenance and other purposes.
• You’re going to use your crawl space as a storage room.

A helpful tip to remember is that there is no one-size-fits-all vapor barrier for crawl spaces. On that note, be as patient and accurate as possible when measuring your crawl space.

Where Does the Vapor Barrier Go in Your Crawl Space?

If it’s the usual method, your vapor barrier should cover at least six inches of height for walls and piers. As for the floor of your crawl space, the entire floor area should be covered.

It’s a different story if you want a total encapsulation for your crawl space, though. Total encapsulation will need your vapor barrier to cover the entire surface of your crawl space.

How Much Does it Cost to Install a Vapor Barrier in Your Crawl Space?

The cost of installing a vapor barrier depends on the type of vapor barrier, measurements of your crawl space, and other materials or tools. On average, this could go from around 1,200 USD to 4,000 USD.

It’s worth noting that the thicker material your vapor barrier has, the more costly it will be. This, of course, is in exchange for better protection and durability.

The average costs of vapor barriers per thickness are as follows:

• 6 mils = 160 USD to 200 USD (per roll)
• 8 mils = 200 USD to 230 USD (per roll)
• 10 mils = 230 USD to 300 USD (per roll)
• 12 mils = 300 USD to 350 USD (per roll)
• 20 mils = 350 USD to 500 USD (per roll)

This is another reason why accurately measuring your crawl space is vital. You wouldn’t want to end up having a lot of excess vapor barriers, as that’s extra money spent for nothing.

Final Thoughts

Installing vapor barriers in your crawl space is a project that needs some preparation and a fairly generous budget. Though, it’s still a good investment since it prevents a lot of health and structural risks.

Your family’s respiratory health is at risk just with the presence of mold. Not only that, but they’re also adept at weakening your house’s durability.

Either way, you and your family will be at risk if you don’t consider the benefits of installing a vapor barrier. You might as well take the effort and save up for such a beneficial project.

Learning how to install vapor barriers in crawl spaces can save you extra money from having to hire professionals. At the very least, you get to protect your family and house while spending less.

Be safe and spend wisely!

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