Wall System Options

One way in which barrier membranes vary is the manner in which they are applied within the wall assembly. The following are a few common barrier types you might encounter.

Self-Adhesive

Self-adhesive membranes are robust, strong choices for a number of reasons. They prevent lateral migration of air, vapor and water, and when there is a breach, the breach stays localized. Air and water cannot travel behind the membrane because the full back surface of the membrane is adhered, and it therefore cannot enter the structure.

Self-adhesive membranes are manufactured with a controlled thickness, are externally reinforced by the surfacing film and require no mixing or special equipment to apply. When working with self-adhesive barriers, keep in mind that they tend to have seams approximately every 3 feet, and they require sealing of the overlaps to avoid fish mouthing. The material is designed to stick to itself, so sealing is easily accomplished. Sheet materials such as these may not be ideal for intricate detailing or for use with complex geometries.

Among the permeable air barrier lines available on the market, self-adhered membranes have varying adhesive properties. An effective permeable air barrier must readily adhere to most building surfaces, so look for an option with strong adhesive qualities, and ideally find one that does not require a primer for its installation to maximize installation efficiency.

Mechanically Fastened

Mechanical fastened air barriers benefit from being relatively inexpensive and easy to install. As is the case with self-adhesive membranes, however, detailing can be complex with mechanically fastened barriers. They are loosely applied, and they are therefore vulnerable to tearing at fastener points. All joint, lap and fastener penetrations need to be completely sealed to provide a continuous barrier to avoid moisture intrusion. Mechanically fastened barriers do not protect against lateral migration of air or water, and they do not transmit negative wind load, meaning their structural integrity many not withstand high suction loads caused by wind being directed around the building at high force.

Mechanically fastened materials are used because the material itself is economical, but it is rarely installed correctly in accordance with manufacturers’ recommendations. When mechanically fastened materials are installed per the manufacturer’s recommended application procedures, the installed cost is similar to that of adhered systems. Adhered materials, however, outperform mechanically fastened materials on all fronts. For example, air and water can travel unrestricted once behind the mechanically fastened membrane. The breach is not contained or localized and the actual source of the breach is nearly impossible to locate. As previously stated, adhered materials stick well to the substrate and prevent the free flow of air or water if a breach occurs. Any breach is contained to an isolated area that is easily detected.

Liquid-Applied

A third type of membrane, a liquid-applied (or fluid-applied) barrier, is typically easy to install and can save time versus sheet material applications. These liquid-applied barriers are seamless, work well on any geometries or applications with intricate details, and require minimal substrate preparation.

The biggest challenge with liquid-applied barriers is thickness control, as it is fully dependent on the installer. Mixing of the material in the container is typically required, and spraying equipment is usually involved, although many of these products may be installed with a roller. There can also be variability with the material, and subsequent application requirements, due to climatic conditions. For example, some materials cannot be installed near freezing temperature, and some may require additives depending on the temperature. There are also differences in composition and the percentage of solids content in liquid materials, and the percentage of shrinkage from wet film to dry film correlates directly to the solid’s content. Be sure to read the product data sheets and installation instructions carefully prior to starting any work.

With numerous types of wall system options available, there is more than one right answer to fit your need. The best option for you is often a matter of preference based on your circumstances and experience. For example, you many have a block structure with brick ties, in which case a liquid may be the best option for the job. Alternatively, you may have a project that requires 40 stories of barrier material where overspray could be a concern, and this application may lend itself to using a sheet material. In general, manufacturers that are dedicated to providing materials designed to protect the entire building envelope will offer sheet materials and liquid-applied barrier options that are compatible and will effectively secure all tie-ins from air-moisture intrusion. If you find a manufacturer you trust, you can likely find reliable materials with the adhesion properties you want.

Conclusion

The ways in which wall systems become wet and ultimately dry are complex, and there is no one simple solution to equipping wall systems with barrier material that is ideal in every situation. Sometimes an impermeable vapor barrier will be needed, sometimes a high-permeability air barrier will work well, and sometimes you will want both. There will also be applications where a self-adhesive sheet material is easiest to apply and will perform admirably, and there will be situations where fluid-applied or mechanically applied barrier material makes the most sense. One thing that is for sure, however, is that any decisions made about vapor control layers should be done in the context of holistic enclosure design.

• Wall systems not only have a positive impact on energy savings, they also create more comfortable environments for building occupants while protecting the integrity of the structure.
  
  
• As showcased in the examples throughout this course, it is important to understand the benefits of and differences between air barriers and vapor barriers, as one option does not fit the needs of every building design and application condition.
  
  
• When designing the correct wall system for any given job, take into consideration climate, geography, conditioning and wall components to determine which wall system assembly will perform best.
  
  
• There are a number of options to consider when choosing a system—from various barrier materials, to wall assembly designs, to adhesion methods that will best suit the application.
  
  
• Whatever materials you choose, be sure they are compatible, will adhere to one another, and will physically transition smoothly from surface to surface to create safe, healthy building environments.

Finally, when you do tackle your next installation, remember to work with a manufacturer that can provide tested solutions on all areas of the structure for the highest likelihood of a successful application. When you are using materials that are designed to be used together, you need not worry about compatibility issues that could affect the longevity of your installation.

Jack Garnett is a Product Manager with SOPREMA.

SOPREMA offers a comprehensive line of roofing, waterproofing, wall protection and civil engineering solutions combining superior products and systems with decades of proven performance. Our solutions include industry leading SBS-modified bitumen membranes, polymeric PMMA/PMA liquid applied membranes and synthetic single ply PVC membranes. www.soprema.us