Buildings are unevenly loaded, particularly where they change height, for example, from single storey to two storeys. Normal seasonal factors, such as moisture content changes in the subsoil, cause different movement between the two parts. The cracks are cosmetic in nature. They are non-progressive but if re- pointed they will recur seasonally.
When a load distribution is uneven, for example when a building changes from singel storey to two storey height, a crack can occur on the intersection.
On sand or gravel soil this can occur soon after construction. Seasonal changes in soil volume cause the building to lift and fall. It is much easier for expansion to lift the single storey part of the building than the two storey parts. A crack occurs roughly in line with the change in load point.
The crack may be straight through the bricks or blocks, or it may follow the mortar joints. This depends on the relative strength of the bricks and mortar.
The cracks are generally minor and uniform in width, although a little rotation may occur causing the crack to taper, being widest at the top and narrow at the bottom. As the crack is only likely to be hairline to 1 mm this will be minor. The crack will not be significant in structural terms and no remedial work is usually required. On exposed elevations however, a small crack might allow moisture penetration. In such circumstances the crack may be need to repair or sealed for this reason. Once a crack has occurred it creates a weak point. If it is re- pointed is likely to recur seasonally on the same line