blocks are usually excluding mortar joints. Block cores are typically tapered so that their top surface (as laid) has a greater surface on which to spread a mortar bed and for easier handling. Most CMUs have two cores, but three- and four-core units are also produced. A core also allows for the insertion of steel reinforcement to span courses in order to increase tensile strength. This is accomplished by grouting the voids of blocks containing rebar with concrete. Thus reinforced, CMU walls are better able to resist lateral forces such as wind load and seismic forces. Cores may also be filled with expanded-polystyrene (EPS) block foam insulation, substantially increasing the R-value of the resulting wall to be in compliance with the US national energy code. A variety of specialized shapes exist to allow special construction features. U-shaped blocks or knockout blocks with notches to allow the construction of bond beams or lintel assemblies, using horizontal reinforcing grouted into place in the cavity. Blocks with a channel on the end, known as "jamb blocks", allow doors to be secured to wall assemblies. Blocks with grooved ends permit the construction of control joints, allowing a filler material to be anchored between the un-mortared block ends. Other features, such as radiused corners known as "bullnoses" may be incorporated. A wide variety of decorative profiles also exist. CMUs may be formulated with special aggregates to produce specific colors or textures for finish use. Special textures may be produced by splitting a ribbed or solid two-block unit; such factory-produced units are called "split-rib" or "split-face" blocks. Blocks may be scored by grooves the width of a mortar joint to simulate different block modules. For example, an block may be scored in the middle to simulate masonry, with the grooves filled with mortar and struck to match the true joints. General information Uses Concrete block, when built with integral steel reinforcement, is a very common building material for the load-bearing walls of buildings, in what is termed concrete block structure (CBS) construction. One of the common foundation types for American suburban houses is the "crawl space foundation" which consists of a concrete block wall around the perimeter on which dimensional lumber floor joists are supported. Retaining walls, which also can be constructed of concrete blocks, either using blocks designed to be set back each course and used with a sand base and without mortar or reinforcing