The Evolution of Thru-Wall Flashings for Masonry Walls

Words: Dan Kamys

By Chris Bupp

Thru-wall flashing is a complete system that includes numerous potential components such as drip plates (item #3), termination bars (item #1), mortar collection devices, pre-formed corners, weeps and vents.

Remember pagers? Remember cell phones the size of a shoebox? Remember when architectural drawings and details were done by hand? One thing we know for sure is that things continually change all around us. The same can be said about construction in general, and especially exterior wall assemblies. It wasn’t that long ago that we never heard the term “building envelope,” but today that term is in everyone’s vocabulary. Today, we talk about air barriers, vapor barriers, and weather-resistive barriers as part of almost every wall assembly conversation. One of the major systems for managing moisture within the building envelope is still thru-wall flashings. More and more, we are – correctly – looking at flashing as a complete system that includes numerous potential components such as drip plates (item #3), termination bars (item #1), mortar collection devices, pre-formed corners, weeps and vents.

Drip plates

With The Brick Industry Association stating in its Technical Notes, “It is imperative that flashing be extended at least to the face of the brickwork,” UV-resistant membranes that can be left exposed are becoming a more popular choice. Still, the masonry industry recommends the use of a drip plate to extend the flashing beyond the outer face of the brick. Normally, this is accomplished with a stainless steel drip plate that extends approximately 3/8 of an inch beyond the face and turned down on a 30-degree angle with a hemmed edge. Aesthetics can be a major problem with stainless steel drip plates. However, newer drip plates are being manufactured with UV-resistant polymers that come in various colors to match a mortar or brick color. I have seen the elimination of drip plates on many projects because of aesthetics. In those instances, the selection of a thru-wall flashing product that can be brought flush to the outside face of the veneer is critical. As steel stud wall assemblies continue to become more commonplace, flashings are being adhered onto sheathing materials, requiring the use of a termination bar with a sealed top edge to prevent moisture from migrating behind the flashing material.

Non-asphaltic adhesives

Technology and innovation have brought us many improved flashing products that are able to withstand the high temperatures in a masonry wall assembly while not being affected by ultraviolet exposure. New non-asphaltic adhesives provide distinct advantages over older rubberized asphalt counterparts of the past, such as eliminating the possibility of staining by the asphalt material, especially when using lighter colored masonry. And even more important is the concern of melting of the asphaltic products under high heat. Today’s newer non-asphaltic flashings have melting points around 300 F; thus the melting or “drool” concern would be a thing of the past. Also non-asphaltic flashings offer compatibility with most non-asphalt fluid applied air/vapor barrier products, especially with the adoption of the NFPA 285 Fire Testing of Exterior Wall Assemblies Containing Combustible Components. This compatibility between the air/vapor barrier materials and asphalt-based flashings has become a major concern and problem for both designers and contractors. When thru-wall flashings and detail tapes are used in conjunction with the air/vapor barrier systems, they also must be compatible with urethane and silicone sealants being used today. Once again, asphalt-based flashings fall short in this area. As we continue to look for products to be used in a cavity wall application that are less flammable and offer greater compatibility with adjacent materials, non-asphalt flashings have surged in popularity.

If you were designing a long-term structure and looking for a “life of the building” flashing product, historically you would have turned to hard metal materials such as stainless steel and copper. Typically, stainless steel flashing systems have been 26-gauge material, which is pre-bent off site based on architectural detail drawings and shipped to the jobsite. Once at the job, the stainless pieces would then be joined together like a big jigsaw puzzle and either soldered or “glued” together to create a watertight system. As you can imagine, this system was very labor intensive, and many times extremely difficult to install properly. Today, new thinner gauge stainless steel flashing products (item #2) have made their way into the market. They still offer the advantage of a material like stainless steel, but with the ability to bend and shape the product in the field, they are installed very much like most membrane flashings. These stainless steel flashing products also are offered with a non-asphalt adhesive similar to a peel-n-stick. Just think, a “life of the building” flashing that is easy to install!

Copper laminated flashings

Copper laminated flashings have been around for many years, and at one time, were the top-selling flashing type used in commercial construction. In the past, the copper material was protected from damage with a woven mesh and a secondary waterproof layer called … you guessed it, asphalt. The asphalt coating has again been replaced with a clear protective coating that offers a non-staining high temperature layer and is much more UV resistant than the older asphalt version. And just like the stainless steel, the newer, clear-coated copper laminated products are now compatible with an air/vapor barrier as well as urethane and silicone sealants. A peel-n-stick version of copper laminate products is available with the non-asphalt adhesive.

Peel-n-stick membrane flashings have become extremely popular mainly because they are easy to install – and also cost-effective. These membrane products have a “carrier” made of polyethylene or similar material. Historically, the adhesive used was rubberized asphalt, which could provide waterproofing and self-sealing characteristics. However, many projects all across the country have experienced the dreaded “drool” of melting asphalt. Therefore, the non-asphalt adhesives have become increasingly popular. Detail tapes used at door and window openings must use membrane materials and non-asphalt adhesives that can provide compatibility and good adhesion with sealants to maintain the continuity of the barrier system.

‘Install-ability’ of the materials

When discussing thru-wall flashing materials, one of the most important criteria should be the “install-ability” of the material with the success of the system largely related to the proper installation in the field. Certainly, a good, high-quality material is essential, but I would argue that just as essential is the ability for the contractor on the jobsite to be able to work with the material and create a total watertight system that includes numerous detail points at inside/outside corners, head and sills of window openings, elevation changes and other transitions. Today, these detail points can be accomplished with preformed detail shapes at inside and outside corners, plus end dams at door and window openings. These preformed shapes make the installation of the flashing system much easier and can dramatically minimize failures at those crucial points. With the development of improved adhesives that can be used with membranes and metal products, the choices of quality and easily installed flashings continues to grow.

Weeps and vents

The main goal of any flashing system is to get the moisture out of the wall. Whatever flashing material is used, we accomplish this with the use of weeps located at every flashing line. Traditionally, plastic tubes and cotton cords were installed 16 inches on center, but they have become much less popular recently, and are giving way to full-height weeps made of honeycomb plastic, aluminum or synthetic mesh spaced 24 inches on center. These more common products are installed into the vertical head joint of the brick course on top of the flashing. Many of these new materials come in various colors to match a mortar color. The cavity area must be kept open and unclogged at the flashing line to allow any accumulated moisture to be able to fall to the weeps via gravity and exit out of the wall. The mason contractor placing a wooden board at the bottom of the cavity had accomplished this in the past, and after a number of rows of brick were installed, this board would be raised up and out of the cavity with any excess mortar droppings being removed to keep the cavity area clean. Today’s mortar collection devices provide a similar level of protection with the use of mesh or grooved materials that will collect the excess mortar droppings while still providing a pathway for moisture to exit the wall. These collection devices MUST be placed at every location within the wall assembly where flashing has been installed. The key factor in a quality product is something that will not clog or potentially create a dam or blockage within the wall. Woven mesh products perform this function quite well.

Another major development in our industry related to moisture management is the concept of ventilating the cavity air space through the use of vents at the top of a cavity wall section in addition to the weeps at the bottom of the section. This combination allows for the circular movement of air in and out of the cavity to allow materials within the wall to dry out. The masonry industry now recommends a 2-inch air space behind the brick to provide a clean, open area for any moisture to more easily work its way to the bottom of the cavity, onto the flashing material and out through the weeps. Ventilation can be accomplished through the use of similar weep-type materials or open head joints. This ventilation concept also lowers the air pressure differential between the outside air and the air with the wall assembly, thus slowing down the moisture drive into the wall.

Obviously, masonry wall design has become increasingly more complex with so many components coming together in the wall assembly. Designers and specifiers must look at all of the various materials and how they interact with each other to provide a complete system approach that can accomplish all the requirements of the 21st century structure. Component manufacturers must be keenly aware of how all of these products must effectively function together, and not just understand their own particular product. Contractors have the ultimate responsibility of constructing these complicated wall systems to manage moisture and give the owner a building that performs up to today’s high-performance standards. While the products of the past served their purposes, technology has brought us improved products using materials that still are user-friendly, but now can answer the biggest concern in our industry today … compatibility.

Chris Bupp is director of architectural services for Hohmann & Barnard and has been involved in the construction industry for more than 28 years with the building envelope as his primary area of expertise. Chris has worked as an independent manufacturer’s rep, a sales manager for a masonry related product company, and as a national speaker and writer on the subject of masonry wall design.




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