Dimensional Limits per UBC

The Uniform Building Code has always set limits on the minimum dimensions of shear walls. This is mainly a result of their desire to limit the deflection of the wall. It also relates to the interaction of the sheathing and framing in narrow walls. The closer the edges come together, the greater the ratio of bending to shear forces in the panel. Bending forces generate tension and compression forces in the plywood layers; forces that are inappropriate where approximately half of the wood fibers are facing the wrong way to accept the force.

Shear Wall Size as defined by the UBC (Table 23-II-1)
Of note here is the vertical gaps between shear wall regions.  The depth of framing is not considered in the height of
shear walls when calculating the height to width ratio.  Where whole shear wall lines are analysed as piers, special
care must be taken to transfer forces around each wall opening.  In general, the costs of creating these transfer paths
far exceeds their benefit.

E Aho Laula

It is important to note that the 1997 Uniform Building Code has changed the dimensional limits on shear walls in seismic zones 3 and 4 to comply with those set for plywood diaphragms. Previously the limit on height to width for plywood sheathed walls was 3.5 to 1.  This ratio has now been reduced to 2 to 1. This will affect future designs and your remodeling options related to future projects.

Comparing Diaphragms and Shear Walls
If a shear wall is half of a diaphragm, then the allowable height to width ratio should
be half of that allowed for diaphragms. This is exactly what the Code recommends;
4:1 for diaphragms and 2:1 for shear walls.