Boundary Walls, Copings and Caps
It is desirable for the sake of economy and time to build boundary and garden walls with relatively thin walling. The problem with such free-standing thin walls is their inherent lack of strength, so they need to be thickened with piers. These are attached at strategic points along the length of the wall, or where additional strength is needed, such as the point where a gate is to be supported.
Attached piers along the length of the wall provide increased strength against lateral forces (for example, wind pressure) that might otherwise overturn the wall. The inclusion of attached piers, their size and frequency along the wall length are directly affected by the height of the wall; the taller the wall, the greater the face area, and the more significant the lateral wind loads that have to be resisted. Tall, slender walls will be more vulnerable, as their height increases in relation to their thickness.
As a general rule of thumb, attached piers are spaced every 3m or so between end piers and/or returns (corners), which act as a buttress.
Walls higher than 2m start to enter the realms of structural design, including the provision of buttressing returns, and this is beyond the scope of this book. The advice here relates only to the more basic, lower structures.