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From Bikes to Buildings: The Importance of Embracing Rainscreen Wall Designs and the New Building Codes.

Words: Keith LolleyPhotos: Advanced Building Products



Have you ever been asked to do a project over the course of your lifetime? For example, when my kids were little, my wife asked me to assemble their bicycles. So, I opened the box, dumped out the contents, and cast aside whatever I thought was unnecessary. Usually, that was the installation instructions. How hard can it be? A frame, two wheels, handlebars, pedals. No problem. Once installation was complete, I noticed the manufacturer always included extra pieces in the box. How thoughtful of them.

Being in the construction industry for over twenty-seven years and speaking with contractors, I noticed we have the same thought process. We do not see a need to follow installation instructions. It looks like a cladding, so it must be installed like every other cladding. Well, many failed wall systems across America have proven otherwise.

Over the years, there have been some great innovations in claddings, both visually and by the materials used to manufacture these claddings; however, many of these claddings are made from absorptive building materials. This is not a terrible thing. We, as designers and installers, just need to plan for these absorptive claddings to, well, absorb moisture. The question is, how do we design these walls to manage moisture intrusion effectively?

The answer is in the building codes, otherwise known as installation instructions. You know, the ones we tend to avoid reading. With ninety percent of all wall failures traced back to moisture-related issues, it is time we started reading and understanding the new building codes.

Recent changes to the 2021 and 2024 International Building Code and International Residential Codes have addressed the need for a capillary break between the backside of the cladding and the front side of the weather-resistant barrier. Moisture will get through claddings made from absorptive materials. The new codes explain proper design techniques to allow these walls to drain and dry effectively. These wall systems are referred to as rainscreen wall designs. Here is the code language taken from the 2021 IRC that I am referring to.

  • R703.7.3.2 Moist or marine climates. In the Moist (A) or Marine (C) climate zones indicated in Figure N1101.7, water-resistive barriers shall comply with one of the following:

  • 1. In addition to complying with Section R703.7.3.1, a space or drainage material not less than 3/16 inch (5mm) in depth shall be added to the exterior side of the water-resistive barrier.

  • 2. In addition to complying with Section R703.7.3.1, Item 2 drainage on the exterior of the water-resistive barrier shall have a drainage efficiency of not less than 90% as measured in accordance with ASTM E2273 or Annex A2 of ASTM E2925.
 

According to the new codes, an airspace not less than 3/16 of an inch is required. How do we go about creating this airspace? Again, the answer is in the installation instructions aka the current building codes. Specifically, ASTM E2925, where it calls out three methods to create this capillary break.

  • Type A – Entangled Mesh Material

  • Type B – Formed/Textured Sheet Material

  • Type C – Formed Battens
Let us review these three options.

Type A – Entangled Mesh Material

These products come in a variety of patterns, colors, and thickness. Manufactured from polypropylene, high-density polyethylene, or nylon six, these products can be manufactured to a variety of compression tolerances and thicknesses depending on the application needed. Most come with a heat-bonded filter fabric. This filter fabric acts as a mortar/scratch coat deflector, which is important for stucco, manufactured stone, or other masonry cladding applications. The filter fabric allows moisture, but not mortar, to pass through, keeping the 3/16 inch air channel clear of debris and allowing for convective airflow from the bottom to the top of the wall. This design not only drains but dries the wall system, keeping surfactants from harming the weather-resistant barrier and excess moisture from the backside of the cladding and fasteners. The filter fabric also doubles as a bug screen at the base and top of the wall. Having a bonded filter fabric to the entangled filaments provides superior shear strength as well. The fabric will not allow the entangled net to stretch, keeping uniformity throughout the surface area of the wall. Another benefit of the heat-bonded filter fabric is the ability to snap a chalk line on the mat and use it as a guide during cladding installation. Entangled net products are pliable, lightweight, easy to work with, compatible with a variety of sealants used in everyday construction, and affordable. Be sure when using or specifying an entangled mesh that it has been evaluated to the ASTM E2925 criteria, which consists of the following tests.

  • ASTM E2925 - Standard Specification for Manufactured Polymeric Drainage and Ventilation Materials Used to Provide a Rainscreen Function
         - ASTM D3045 – Heat Aging
         - ASTM D5199 – Nominal Thickness Test
         - ASTM D5322 – Immersion Procedures
         - ASTM D 6108 – Compression Testing
         - ASTM D 6364 – Short-Term Compression Testing
         - ASTM E84 (Class A) – Surface Burning Test
         - ASTM E2273 – Drainage Efficiency
         - ASTM G 154 – UV Testing
 



Type B – Formed/Textured Sheet Material

These products come in a variety of colors and configurations as well. Commonly used in below grade and horizontal applications because of their compression strength, these products can also be used in sidewall applications. Often Type B products are designed with dual drainage and ventilation on the front and back side of the product and allow multi-directional drainage similar to entangled mesh; however, there are some Type B products designed with drainage and ventilation on just one side and are not multi-directional. Review the data sheets before specifying and installing. Again, make sure Type B products have been evaluated to ASTM E2925 before specifying.



Type C – Engineered Batten Strips

In recent years there have been innovations in engineered batten strips. Some have dual drainage and ventilation on the front and backside of the batten. This reduces surface to surface coverage where moisture could otherwise remain trapped.

Engineered battens are uniform, which means they are all the same dimensions reducing the need for cutting and shimming on a job site. Engineered battens have cross ventilation capabilities as well. They can be installed vertically or horizontally and work effectively. Be sure the engineered batten you are considering has been evaluated to ASTM E2925.

Now that we know the language in the new building codes and what type of products are acceptable, join me online through Masonry Design Magazine next month when we talk about the proper way to install these products.





About: MAP Partner
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