Three-dimensional (3D) sandwich precast concrete walls are often used in building construction due to their superior performance, thermal efficiency, and speed of fabrication. When applied to low-rise buildings, this technology facilitates a cellular structure composed of squat sandwich walls sustaining gravity loads and performing as shear wall against lateral loads. Not much research information is available on squat 3D sandwich walls under in-plane lateral loading. This paper discusses experimental investigations on eight squat 3D sandwich walls were tested, in which four were without and four with boundary elements. In each group of four walls, two were provided with only weld mesh as reinforcement and remaining two were provided with additional longitudinal reinforcement. The shear span-to-width ratio of walls was 1.0 or 0.87 subjected to lateral quasi-static reversed loading cycles, while the vertical load was kept constant. The dimensions of unstiffened 3D sandwich walls are 1250 mm × 1250 mm, whereas the dimensions of the stiffened 3D sandwich walls are 1125 mm × 1250 mm (size of stiffening element: 370 mm × 1250 mm). The behavior of squat 3D sandwich walls has been investigated in terms of load–displacement response, crack pattern, mode of failure, ductility, stiffness degradation, and energy dissipation. Also, the present study attempts to validate the current design practices, both in Europe (Euro code 8) and in the United States (ACI 318) in relation with the experimental results. Also, other available design equations established for reinforced concrete walls to verify the applicability of these empirical formulae for sandwich walls have been examined. From the test results on 3D sandwich walls, it has been observed that the addition of longitudinal reinforcement and the boundary elements exhibited strong coupling action of shear due to the squat nature of the walls. The 3D sandwich walls with additional longitudinal reinforcement showed significant strength and stiffness. © The Author(s) 2017.