shift

In masonry and brickwork, shift is the horizontal distance by which successive courses are offset relative to one another. When bricks, stones, or planks are laid in courses (horizontal rows), the vertical joints between adjacent units in one course should never align with the joints in the course directly above or below. Shift ensures this offset occurs, so no continuous vertical line of mortar runs through the wall, which would create a plane of weakness.

The principle is called breaking joints. A wall laid without shift will fail prematurely under load or water infiltration, because the aligned joints create a preferred path for cracking and for water to penetrate between the stones or bricks. A minimum shift of one quarter of the unit length is conventional in most masonry codes and practices. In a stretcher bond pattern using standard bricks, for example, each course is typically set back by half a brick length relative to the one below, producing a clear, regular pattern of broken joints.

Common patterns and constraints

Shift is controlled by the chosen bond pattern: stretcher bond, header bond, English bond, Flemish bond, and others each produce different shift geometries. Random or coursed rubble masonry also requires careful attention to shift, though the offset may be less uniform. The goal remains identical: no more than two courses in a row should share a joint line. When shift is too small or absent, the wall is said to have poor bond and will exhibit reduced strength and durability.

Shift also matters in roof and floor construction where planks or boards overlap in multiple layers. The term carries the same meaning: the overlapping arrangement offsets the end joints between layers so that loads are distributed across the full width of the structure rather than concentrated along a seam.