Despite their poor performance, non-standard clay bricks are commonly used in construction of low-rise buildings and rural houses in Indonesia. These clay bricks are produced traditionally in home industries. Indonesia is located in an active seismic region and many masonry buildings were badly damaged or collapsed during recent earthquakes. Such buildings are classified as non-engineered structures as they are built without using any proper design standard. Lateral load response of un-reinforced masonry walls is investigated in this research project, with the aim of better understanding the behaviour of these masonry walls using low quality local bricks. A comprehensive experimental program was undertaken with masonry wall elements of 600 mm x 600 mm x 110 mm constructed from local bricks from Cikarang in West Java - Indonesia. Wall specimens were constructed and tested under a combination of constant vertical compression load and increasing horizontal or lateral in-plane loads, of monotonic, repeated and cyclical nature. The vertical compressive loading was limited to 4% of maximum brick compressive strength. Masonry mortar mix used to construct the specimens was prepared according to Indonesian National Standard. Three different types of masonry wall panels were considered, (i) (normal) brick masonry walls, (ii) surface mortared brick masonry walls and (iii) comforted surface mortared brick masonry walls. The results indicated that the lateral load bearing capacity of masonry wall is usually lower than that of mortared and comforted walls. Despite this, the lateral load capacity under cyclic loads decreased 50 % of the average capacity of the walls under monotonic and repeated lateral loads. Using the results from the experimental program, a simplified model for the equivalent diagonal spring stiffness of local clay brick walls was developed. This stiffness model derived from experimental results in then used to simplify the structural analysis of clay brick wall panels in Indonesia. The design guideline for brick masonry houses and low-rise buildings in six Indonesian seismic zones was developed, as a contribution towards the development of design guidance for constructing brick masonry houses in Indonesia.