Copyright Goodheart-Willcox Co., Inc. Chapter 14 Wall Systems 309 The thermal expansion properties of concrete, stone, and terra cotta are similar to those of brick masonry, and these materials usually do not pose extreme problems with differential movement when applied as caps and copings. Corbels and Racking A corbel is a shelf or ledge formed by projecting successive courses of masonry out from the face of a wall. Corbeling of brick masonry is done to achieve a particular appearance or to provide structural support. The total horizontal projection should normally not exceed one-half the thickness of a solid wall or one-half the thickness of the veneer of a veneered wall. The projection of a single course should not exceed one-half of the unit height or one-third of the unit bed depth, whichever is less. Code Note Corbel Projection Limitations The International Residential Code (IRC) speci- fies that the maximum corbeled projection beyond the wall face should not exceed the following: • One-half of the wall thickness for multiwythe walls bonded by mortar or grout and wall ties or masonry headers. • One-half the wythe thickness for single wythe walls, masonry-bonded hollow walls, multiwythe walls with open collar joints, and veneer walls. Racking is masonry in which successive courses are stepped back from the face of the wall. When racking back to achieve the desired dimensions, make sure the cores of the units are not exposed. Segmental Retaining Walls and Hardscape Segmental retaining walls (SRW) are constructed of high strength concrete blocks or units made specifically for dry stacking without the use of mortar. SRW blocks are used to build retaining walls for commercial and residential applications. Retaining walls and other masonry landscaping materials are sometimes called hardscape. See Figure 14-71. This term can refer to concrete retaining wall materials, piers, dividing walls, pavers, and caps for walls and piers. Hardscape is made similar to concrete block, but is intended for decorative applications and is laid on a gravel and sand base. Hardscape can be purchased in numerous sizes, shapes, and colors. Retaining walls, tree rings, planters, and edgings can be made from concrete masonry units that have a locking lip on the lower back edge. See Figure 14-72. The units are placed so the lip locks behind the course below to provide proper alignment and prevent forward movement exerted by earth pres- sure. Typical retaining wall products include straight and beveled front units with uniform or tapered widths. See Figure 14-73. Brick Industry Association Figure 14-70. Terra cotta coping for a parapet wall. The coping slopes toward the roof to deflect water from the front of the building. Terra cotta coping Full collar joint Z ties Flashing and counterflashing Rigid insulation Anchor Wall Systems, Inc. Figure 14-71. These mortarless masonry units provide a significant amount of flexibility in laying up straight or curved retaining walls.