Wavy walls, also known as crinkle crankle walls, use fewer bricks than straight walls because they can be made thinner and still provide stability. The wavy design allows for a single layer of bricks, while a straight wall would require additional support or thickness to withstand lateral forces. This type of wall is commonly found in England and was also used by Thomas Jefferson in the United States. The wavy design provides stability and helps the wall resist wind and other external forces.