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How the pros mount the SIGA Majrex smart vapor barrier

Level up your Majrex smart vapor barrier installation with these steps.

Every vapor barrier is different. 

When you’re making your pick, the decision should be based on two factors:

  • The location of the product in your wall assembly
  • The permeability you need based on your climate

SIGA Majrex is a smart directional vapor retarder that limits moisture transportation into the wall cavity and at the same time maximizes inward drying. The result is a dry and mold-free roof, wall, or floor over the lifetime of the building.

Quick Tips for Installation

  • The printed side of the smart vapor barrier displaying the dash lines and SIGA Majrex label must face toward the installer into the room. The blank side of the smart vapor barrier should face into the wall assembly detail and away from the installer.
  • Overlap sheets by 4 inches, both vertically and horizontally.
  • Install the Majrex flat and without tension. There should be light slack at the inside and outside corners for tension relief.
  • The Majrex smart vapor barrier is suitable for containment of loose-fill insulation with adequate structural blocking and proper venting. Click here for the Majrex system guidelines for more info.
  • All insulation (except loose fill) should be installed before mounting the Majrex.
  • Seal using only SIGA system components.
  • Repair any small damages to the Majrex with SIGA Rissan 60.
  • All non-service cavity installations, plumbing and electrical should be completed before installing the Majrex.

How to Mount on Wood or Metal Framing with Twinet Mounting Adhesive

Before mounting the SIGA Majrex you’ll need to have your Twinet mounting adhesive installed on the wood or metal studs.

Twinet is a ¾ inch mounting tape that is pressure sensitive and reinforced with acrylic adhesive and an embedded fiber-strand layer. It’s primarily used for mounting vapor control layers to building frames and panel goods.

Step 1: Measure the Space

Starting from any wall corner, measure across the length of the wall. Make sure to extend your SIGA Majrex 6 inches past any inside or outside corner to provide enough material for necessary overlaps.

Measure the SIGA Majrex

Once you have your material measured out, follow the print guidelines to cut a straight, clean line.

The guidelines are there to help you measure necessary overlap, but they also provide you an easy path to follow to get the straightest line possible in the field, so you’re not wasting material.

The dash lines at the top and bottom of the Majrex are four inches apart (blue arrows), which is our required overlap.

The other dash lines are 1.25 inches from the factory edges at the top and bottom and work as your tape centering guidelines (green arrows).

The plus signs are 10 centimeters apart.

SIGA Majrex plus signs 10 centimeters

The distance between one large dash line and another is one meter.

SIGA Majrex distance between dash lines 1 meter

Step 2: Cut into the Twinet at 59 inches or Make a Leveling Line

Make a cut into the Twinet using your razor knife at the top of where your membrane is going to fall. It will allow you to start working with the lower portion of the wall.

However, another option would be to make a leveling line at 59 inches, the height of the Majrex roll. 

Each option provides you a guide for installing your Majrex smart vapor barrier level.

Step 3: Remove the Twinet Backing and Apply Majrex to Adhesive on Bottom Row

Working on the bottom half of your wall assembly, remove the backing on your Twinet to expose the adhesive.

For an easier install, only remove half of the backing, starting at the top. This will allow you to apply the Majrex to the exposed adhesive along the top of the first run of Majrex. As a result, you’ll be able to adjust the smart vapor barrier as needed for a flat installation.

Tip: You can use your razor knife to hook the Twinet backing to remove it quickly from the adhesive.

Press the Majrex onto the exposed Twinet adhesive, firmly moving across the wall assembly at the top.

Once the Majrex is mounted at the top of the first run, start in the center stud and reach under to remove the remaining Twinet backing.

If you ever have too much tension and can’t pull the backing from the middle of the run where you left off, you can pull the backing, starting at the bottom.

Once you have the adhesive exposed, begin pressing the Majrex firmly along the entire length. Repeat the process, moving outward from the center stud.

Tip: It’s easier to work on one stud at a time instead of removing the backing on all the studs and going back to apply the Majrex. Starting on the center stud provides support and increases the chance of a non-wrinkled install.

Step 4: Check your Horizontal Overlap

Make sure your rows of Majrex have a four-inch horizontal overlap to create a continuous smart vapor control layer.

Once you’ve confirmed you’re ready to move forward with the install on the next row of Majrex.

Step 4: Remove the Twinet Backing and Apply Majrex to Adhesive on Top Row

Pull the Twinet backing down from the top to where you can reach it from the ground.

Roll your Majrex out across the wall assembly, pressing it firmly to the exposed adhesive and covering the studs from one side to the other.

Once the Majrex is installed along the top of your wall assembly, start pulling the Twinet backing off on the middle stud and applying pressure to secure the Majrex fully. Repeat this process for the remaining studs, working to the right or the left.

And there you have it. The complete process for installing the Majrex smart vapor barrier on a wood or metal stud using Twinet mounting adhesive.

But what happens if you’re mounting the SIGA Majrex on wood with T50 staples? 

The process looks similar but has some key differences.

How to Mount on Wood with T50 Staples

Step 1: Measure the Space

Starting from any wall corner, measure across the length of the wall. Make sure to extend your SIGA Majrex 6 inches past any inside or outside corner to provide enough material for necessary overlaps.

This step is the same process you’ll experience if you’re installing using SIGA’s Twinet mounting adhesive.

Measure the SIGA Majrex

Once you have your material measured out, follow the print guidelines to cut a straight, clean line.

Step 2: Staple Majrex Along Leveling Marks

Create a leveling line at 59 inches, the height of the Majrex roll. Align the Majrex smart vapor barrier along the leveling marks and staple at the top edge of each stud.

TIP: Maintain plumbing alignment and avoid tension when installing the Majrex to the wall.

Step 3: Staple Each Vertical Stud

Continue stapling along each vertical stud.

How far the staples are spread apart depend on the insulation you’re planning on using. 

Staple every 4 inches for batt insulation.

SIGA Majrex staple every 4 inches for batt insulation

Staple every 2 inches if you’ll be installing loose-fill (blown-in) cavity insulation afterwards.

SIGA Majrex staple every 2 inches for loose fill insulation

Step 4: Check your Horizontal Overlap

Make sure your rows of Majrex have a four-inch horizontal overlap to create a continuous smart vapor control layer.

Once you’ve double checked your overlap you’re ready to move forward and install the next row of Majrex.

Step 5: Repeat Stapling Process for Every Majrex Row

Repeat the stapling process using the printed guidelines on the Majrex to ensure accuracy for every needed row of Majrex for a continuous vapor control layer.

Step 6: Cover Staples with Rissan (Optional)

If you’re attempting to achieve superior air sealing along with your vapor control, it’s recommended to cover each staple with Rissan air-sealing tape.

Conclusion

By following these instructions, you’ll be a pro at installing the SIGA Majrex in no time and on your way to producing smarter, more comfortable buildings.

Have questions about the SIGA Majrex smart vapor barrier? Contact our team to discuss your project or download our Majrex system guidelines for more details.

Majrex System Guidelines How to Install the SIGA Majrex

Jessica Kumor

Jessica is SIGA North America's Content Marketing Manager. It's her job to deliver you the latest research and practical tips for building air and weathertight buildings. When she's not interviewing customers and posting about building science you can find her refinishing furniture.

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