A simple theory is proposed for the structural design of the seismic reinforcement for adobe houses, typical of Peru and other Andean countries. The reinforcement consists of welded meshes added over the adobe walls, in order to simulate confinement beams and columns. This kind of reinforcement was applied to existing houses in 1998 in Peru and later in other Andean countries. The reinforced adobe houses located in the areas affected by the earthquakes of 2001 and 2007 in Peru had a good structural behavior, while neighbor houses suffered heavy damage. This paper shows how the out-of-plane seismic forces in the adobe walls can be resisted by meshes located at the corners and longitudinal meshes. The hand calculations of the forces were verified with a finite element computer model, with close results.