Copyright Goodheart-Willcox Co., Inc. Chapter 14 Wall Systems 283 differences between the mean maximum and mean minimum temperatures of the outer wythe of the cavity wall, as well as the absence of restraint usually provided by dead and live loads, masonry bonders, or filled collar joints in solid walls. For this reason, it is recommended that expansion joints be provided through the outer wythe of the cavity wall on each side of an external corner where the walls are 50′ or more in length. Where possible, the expan- sion joint can be placed in line with the jambs of the windows nearest the corner. Hollow Masonry Bonded Walls Hollow masonry bonded walls are walls used as foundation and exterior loadbearing walls. They are popular in some parts of the United States. Though economical, they are not resistant to high moisture. See Figure 14-11. Anchored Veneered Walls Brick and stone masonry units are widely used as facing veneer. See Figure 14-12. In this applica- tion, the loadbearing properties of the materials are not used. The veneer is attached to the backing, but does not act structurally with the rest of the wall. In anchored brick veneer construction, a nominal 3″ or 4″ thick exterior brick wythe is anchored to a backing system with metal ties. There is a clear air space between the veneer and the backing system. The backing system may be constructed of wood frame, steel frame, concrete, or masonry. A veneer wall has a facing of masonry units or other weather-resisting, noncombustible materials. The facing is securely attached, but not bonded to, the backing. See Figure 14-13. Brick veneer is designed to carry loads due to its own weight, but also needs to resist wind and seismic conditions that contribute stresses to the brick veneer. The manufac- turing and installation of brick should conform to ASTM C62, ASTM C216, or ASTM C652 for building brick, facing brick, and hollow brick, respectively. Two sources that discuss brick veneer design, procedures, and practices are MSJC Code Chapter 12 Veneer and BIA Technical Notes on Brick Construction 28B, Brick Veneer/Steel Stud Walls. Both are valuable resources when planning brick veneer. Trade Tip Salvaged brick is not recommended for use as brick veneer. At one time, brick veneer construction was mainly limited to wood frame houses. It is now being used on low-rise commercial and institutional construction and is frequently used for high-rise buildings, especially with concrete masonry or steel stud backing systems. Veneer wall construction looks much like cavity wall construction in its final form. However, the construction and function are considerably different. For example, the supporting structure in a veneer wall is completed before attaching the veneer, which is not loadbearing. Both wythes in a cavity wall are loadbearing and are built at the same time. Goodheart-Willcox Publisher Figure 14-11. Hollow masonry bonded walls. Header course Header course Header course Header course Goodheart-Willcox Publisher Figure 14-12. Brick and stone veneer attached to frame construction using metal ties. These veneers must rest on an extension of the foundation. Brick Veneer on Frame Stone Veneer on Frame