Vapor Barrier Installation 101

By: Contributors  | 
Close up of a person installing vapor barrier around the skylight in the attic of a house.
Installing vapor barrier isn't as difficult as you might think, but it's incredibly important to the longevity of your home.
brizmaker / Shutterstock

A vapor barrier is an essential part of a building, but it’s often installed incorrectly or omitted entirely. Fortunately, vapor barrier installation isn't as complex as it may seem.

When it comes to protecting your home from the damaging effects of moisture, few things are as critical as a properly installed vapor barrier. But what exactly is a vapor barrier, and why is it so important in building construction?


Essentially, a vapor barrier is a material used to block moisture, and prevent water vapor and mold spores from penetrating walls, ceilings, crawl spaces, and floors. It's an essential component in maintaining the integrity of structural elements of a building, preventing mold growth, and ensuring a healthy living environment [source: Wallender].

Vapor barriers can be made from various materials, including plastic sheeting, foil, and coated paper. Each type is designed to control the diffusion of moisture through walls, though the choice of material often depends on specific conditions and requirements.

This guide will cover the basics of vapor barrier installation, from selecting the right type of barrier to the final touches of sealing it in place. Understanding the role of proper installation is an investment in the longevity and health of your home. So take care to learn as much as you can.


Tools and Materials

Preparation is a key component of any installation project. When it comes to installing vapor barriers, preparation starts by gathering the necessary tools and materials.


  1. Utility knife
  2. Staple gun (and staples)
  3. Tape measure
  4. Chalk or line marker
  5. Scissors or shears


Vapor barrier sheet, which is available in various materials:


  • Polyethylene plastic sheeting, which is common in residential construction and ideal for most climates [source: U.S. Department of Energy].
  • Foil-backed paper, which is often used in colder climates.
  • Metalized film, which is used in applications that require peak durability and longevity.

Sealing tape

Acoustic sealant or caulk


Preparing for Installation

Now that you've assembled the necessary tools and materials, it's time to prepare the area for installation. For the purposes of this demonstration, let's pretend that you're planning on installing crawl space vapor barriers.

Assess the crawl space by inspecting the walls, ceilings, and floors where the vapor barrier will be installed. This is also a great opportunity to measure the area to determine how much material the job requires.


Next, you'll want to keep your crawl space clean by removing any dirt, dust, debris, and any loose material. This is also a great time to repair any cracks or holes in the walls or framing that can compromise the effectiveness of vapor barriers.

Finally, before you start, you'll need to read up on any local building codes to ensure compliance with any specific requirements to vapor barrier installation in your area.


Step-By-Step Installation Instructions

Now that the area is prepared and you have all your tools and materials on hand, it's time to begin the actual installation. Follow these steps to ensure a secure and effective installation [source: Shannon-Karasik].

Unroll and cut the vapor barrier:


  • Measure and cut: Unroll the vapor barrier material and measure it against the area you are covering. Cut the material to size using your utility knife or scissors.
  • Leave extra material: It's recommended to cut the vapor barrier slightly larger than the area to ensure complete coverage and allow for overlap at the seams.

Attach the vapor barrier:

  • Start from the top: Begin at the top of the wall or ceiling and gradually work your way down.
  • Use the staple gun: Secure the vapor barrier to the framing using the staple gun.

Overlap seams:

  • Ensure overlap: When you need more than one sheet, overlap the edges by at least 6 inches.
  • Seal the seams: Use the sealing tape along overlaps to ensure that prevent moisture problems.

Properly seal the edges: Use acoustic sealant or caulk along the edges of the vapor barrier where it meets floors, ceilings, and corners.

Inspection: Once the vapor barrier is fully installed, inspect it thoroughly. Look for any tears, gaps, or areas where the barrier may no be fully sealed.


Ensuring a Moisture-Safe Environment

Congratulations! You just learned about one of the most crucial steps in safeguarding your home from ground moisture. The installation of a vapor barrier is a commitment to the longevity and health of your living space. By carefully following the steps outlined above, you can effectively control moisture, and protect your home from the potential dangers that come with it.

It's important to remember that the effectiveness of a vapor barrier lies not only in the quality of the material, but also in the precision of its installation. But the work doesn't stop at installation. Regular inspections and maintenance can help ensure that it continues to function effectively for years to come.


If, after reading this, you feel less enthusiastic about your chances of successfully addressing crawlspace moisture yourself, that's alright too! There are plenty of vapor barrier experts nearby, ready and willing to tackle your crawl space vapor barrier project.