How To Install 2-in-1 Vapor Barrier Flooring Underlayment

In this illustrated step-by-step guide we will show you how to install 2in1 Vapor Barrier Flooring Underlayment. 2in1 Vapor Barrier Underlayment is a combination of the standard underlayment sealed with a moisture barrier attached on the bottom. The moisture barrier prevents moisture from getting into the flooring and potentially causing major damage. Vapor barrier underlayment is used whenever there is possibility of moisture coming up from the sub-floor. 2in1 Vapor Underlayment is rolled over the subfloor prior the floor installation. It is suitable for several types of floating flooring including laminate flooring and engineered wood floors.

Note: If you are installing flooring with a pre-attached underlayment, don’t use 2in1 underlayment; use Visqueen 6Mil PE  Vapor Block Film instead.

2-in-1 Vapor Barrier Underlayment Installation Guide:

Installation of the 2in1 Vapor Barrier is not complicated and we will walk you through it. Follow our illustrated step-by-step guide and become an expert!

Before starting the installation, be sure you have all necessary tools and supplies ready. Be certain to have a thorough understanding of the scope of the project and the expectations of time of completion before starting the job. Good organization will save your time and energy!

One more advice before starting: as with all flooring installations, the site must be climate controlled for at least 48 hours before the installation. The room temperature should be at least 65°F and the relative humidity should not exceed 65%.

Are you ready? Let’s get started!

Step 1: Organize Your Installation Materials

You will need:

  • 2in1 Vapor Barrier Underlayment
  • Flooring (laminate floor, engineered wood, or any other type of floating floor)
  • Broom & Dust Pan
  • Tape
  • Scissors or Utility Knife
    How To Install 2in1 Vapor Barrier Underlayment:Tolls and supplies you need
    Tools and Supplies You Will Need

Step 2: Clean The Jobsite

Laminate flooring can be installed over existing vinyl, wood or ceramic floors. Remove carpet or any other type of the existing flooring with a cracked, damaged, or uneven surface. The surface you will be working with must be perfectly flat & clean. Take your broom and sweep up all dust and debris before continuing the installation.

How To Install 2in1 Vapor Barrier Floor Underlayment: Clean your subfloor
Clean Your Subfloor

Step 3: Inspect And Fix The Subfloor

The structural integrity and the flatness of your subfloor is critical for a satisfactory flooring installation and performance. Your subfloor must be free of defects. Make sure that the concrete subfloor is level, flat, structurally sound, and dry. The subfloor must be level and flat within 3/16” over a 10’ span. Faulty areas should be repaired to have the best results and a smooth laminate surface.

Concrete subfloors must be at least one month old prior to installation. Before installation, a calcium chloride test must be performed. The maximum allowable reading on this test is 5 lbs./24 hours/1,000 square feet.

How To Install 2in1 Vapor Barrier Floor Underlayment: Inspect your subfloor
Inspect your Subfloor

Step 4: Install Underlayment

Once your subfloor is inspected, repaired, and prepared, you are ready to start your installation. 2in1 Underlayment comes in rolls and has an overlap on one side of the roll. Unroll one width of the 2in1 Vapor Underlayment. The yellow plastic film should face the subfloor and the overlap should be on the opposite side of the wall.

How To Install 2in1 Vapor Barrier Underlayment: Unroll the first row
Unroll The First Roll – plastic-side down, with the overlap strip facing away from the wall

Step 5: Cut Your Underlayment

After rolling your underlayment out from wall to wall, measure and cut your first section to fit accordingly. Remember to measure twice and cut once!

How To Install 2in1 Vapor Barrier Underlayment: Merasure and cut your underlaymet
Measure and Cut Your Underlayment

Step 6: Add Flooring

As you move forward with your underlayment installation, add the flooring. Stop flooring installation when you reach a distance of 1 foot from the edge of the underlayment.

How To Install 2in1 Vapor Barrier Underlayment: Stop installing your flooring when you are 1 foot from the edge of the underlayment
Stop Installing Your Flooring When You Are 1′ From The Edge
Tip: Make sure to acclimate your flooring at least 48 hours before the installation. Cross stack your floor in original packaging. Room should have at least 65°F and the relative humidity should not exceed 65%. Cartons should not be opened until time of the installation since atmospheric conditions may alter the product, thus making it more difficult to install. Always handle cartons carefully so you will not damage the product inside.
Cross Stack Flooring Boxes To Acclimate
Cross Stack Flooring Boxes to Acclimate for 48 Hours

Step 7: Roll Out Next Row of Underlayment

Just like Step 4, unroll another section of underlayment right up against the previously installed underlayment section. Measure and cut accordingly. You may be tempted to continue laying down underlayment – Do not lay down everything at once. This way you will have full control of your project and seamless, moisture-resistant connections between each of the sections.

How To Install 2in1 Vapor Barrier Underlayment: Unroll your second row
Unroll Your Second Row Covering The Overlap

Step 8: Use Attached Overlap

When unrolling your rows, install your next row on the top of the overlap, however be sure to not overlap the foam edges. Using the attached overlap creates a seamless moisture seal between rows when properly installed.

How To Install 2in1 Vapor Barrier Underlayment: Butt the rows together
Butt the Edges of the Underlayment Together
How To Install 2in1 Vapor Barrier Underlayment: Don't overlap the foam
Do NOT Overlap the Foam

Step 9: Securely Tape The Seam

Use packing tape to seal the rows together – this will keep your 2in1 Vapor Barrier Underlayment in place and assure the functionality of the vapor barrier.

How To Install 2in1 Vapor Barrier Underlayment: Tape the rows together
Tape the Rows Together

Step 10: Repeat!

Continue and repeat Steps 4 to 9, installing underlayment and flooring together. Make sure to follow installation instructions provided by the manufacturer of the flooring.

How To Install 2in1 Vapor Barrier Underlayment: Install your floor on the top on the underlayment
Repeat Steps 4 – 9 until Installation is Complete

Now you should be know how to install 2in1 Vapor Barrier Flooring Underlayment, however if  you have additional tips that you think we should include in this guide, please let us know! Share your tips and experiences in the comments below!

More Installation Tips:


  1. Thank you so much for this article. It was easy to understand. I am ready to begin!

  2. Hey Billy! You can slightly run the padding up the wall to ensure it is under the floor completely, obviously just trim it when the floor is fully laid! Thank you for reaching out.

  3. Thanks for the article,
    I was just wondering if the vapor barrier needs to be stuck to the wall in some way. Would the damp not find a a way of working its way around the edges?

  4. Thanks! Glad it was helpful Koli.

  5. thanks your sharing. really useful..

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