Masonry Anchoring Systems: Today and Beyond
Changes in wall construction have impacted how anchoring systems are used
By Chris Bupp
Today's masonry walls are complex and sophisticated, incorporating an updated set of concepts and materials that, when designed and constructed properly, create sustainable, energy-efficient and environmentally friendly masonry wall systems, far surpassing those of the past. Even though substantial changes in the theory and practice of cavity wall construction have occurred, one thing has remained constant: the importance of the anchoring system and its essential role of holding the veneer in place for the life of the structure. Changes in cavity wall construction include the increased use of air and vapor barrier systems, metal stud assemblies, cavity ventilation, oversized veneer units, and the use of rigid insulation instead of batt insulation. All of these changes in how walls are built have significantly impacted how anchoring systems are being used today.
When discussing anchor systems, a current key issue is the relationship between the anchor and the air/vapor barrier. The anchor and barrier material must be able to create a completely airtight connection. Essentially, the air barrier must be able to self-seal openings from penetrations that anchors can cause. Because of this requirement, self-adhesive sheets and fluid-applied materials have dramatically increased their shares of the current air/vapor barrier market, overtaking the building wraps of the past, due to the inability of building wraps to self-seal and maintain a continuous air/vapor barrier.
With numerous types of anchors on the market, especially for steel stud assemblies, and anchor styles that feature either a single attachment or dual attachment, it can be difficult for designers to verify whether a product will successfully maintain a properly sealed connection with the air/vapor barrier. Testing is required confirm that an anchor system can fulfill the requirements of the modern masonry wall. This is being accomplished with the new ASTM E-2357 testing method, which is the standardized method for determining air leakage of air barrier assemblies. This testing procedure should give peace of mind to both the designer and installer, that the anchor system they have specified, if properly installed, will function as intended.
Another significant issue these days is the increased width of many wall cavities. This increase is occurring because of two major reasons. First, the masonry industry now recommends a two-inch clear air space behind all veneer systems. Second is the ever-increasing desire for energy-efficient buildings, which require thicker units of rigid insulation. Designers have been moving away from batt insulation in steel stud assemblies to rigid insulation in the cavity as a way to push the “dew point” of the wall assembly outboard of the sheathing material, plus rigid insulation creates a more continuous layer of protection from the elements. Additionally, the move toward rigid insulation in the cavity is being prompted by code requirements in certain states and, potentially, a national code change in the near future. The Brick Industry Association states that 4.5 inches is the maximum dimension from the outer face of CMU or sheathing to the back side of a veneer material that can be handled by a “standard” anchoring system. Anything over 4.5 inches requires an “engineered anchoring system.” In many northern parts of the country, insulation amounts already have created cavities well over the standard category. High-strength anchoring systems are necessary to meet these newer design requirements created by increased wall cavity widths, and have become absolutely essential in areas with high-wind loads, especially when they are used in multi-story structures. Seismic activity, and its potentially detrimental effects on masonry walls, as seen recently in the tragic events in Haiti, also requires the use of high-strength products that can withstand the punishment of natural disasters. High-strength systems generally include heavier gauge wire and metal components that require specialized manufacturing to meet today’s stricter codes.
To avoid corrosion and maintain the longterm integrity of the exterior masonry wall, reinforcement and anchors need to be either hot-dip galvanized or stainless steel. Interior masonry walls can still use a mill-galvanized finish, but the trend in the industry is for all reinforcement to be a minimum of hot-dip galvanized to prevent confusion over the material type on the jobsite. The use of stainless materials is rapidly growing and strongly recommended for stone veneer applications. For wall reinforcement, truss type reinforcement is a stronger product, due to its greater effective steel area. However, the ladder type has become increasingly popular, because of its ability to handle more movement and deflection in the wall. More important, as more masonry walls incorporate vertical reinforcement, the design of the ladder type allows for the cores of the block to remain open, so as not to interfere with the placement of the vertical rebar. Wire diameters of nine-gauge or 3/16-inch are available for these applications.
Two major points to consider when selecting an anchoring system are the vertical adjustability factor and the potential for disengagement. Vertical adjustability describes how much flexibility an anchoring system can give the contractor to effectively place the anchor, so that the tie can line up with the veneer joint. This is especially important when using oversized veneer units, and even more so when combining different product types into a single veneer. Disengagement of the anchor through normal wall movement has become another hot topic, and many new products on the market today address this issue for both CMU and steel stud wall assemblies.
For many years, the industry has followed the standard veneer wall construction of the ACI 530/ASCE 5/TMS 402, and this excerpt, “the anchor must be capable of withstanding 100# load in tension and compression without deforming or developing play in excess of 0.05,” has been used to describe the requirements of an anchoring system. But, as you may have already guessed, the days of “picking an anchor out of a catalog” are quickly becoming a thing of the past. The requirements for every project need to be reviewed when selecting a suitable anchoring system to meet the demands of today’s masonry walls. Strength, movement capability, adjustability, and air barrier interface are all items that need to be considered.
With all of the components involved in the modern masonry wall, perhaps the most important factor to consider is the compatibility of all elements going into the wall assembly. With so many anchor types, air and vapor barrier materials, and flashing products on the market, it is becoming increasingly difficult for both architects and contractors to determine what constitutes a high-quality assembly.As the industry evolves,“complete systems” with single-source warranties should become popular, similar to the roofing industry with independent testing and compatibility requirements for all components.
About the Author
Chris Bupp is architectural and educational service director for Hohmann and Barnard.