How much shorter should setting blocks for curtain walls be compared to the full width of the rabbet?

The correct length for setting blocks used in curtain walls is typically 1/16 inch shorter than the full width of the rabbet. This slight reduction is important because it allows for proper expansion and contraction of the materials during temperature fluctuations. By having setting blocks that are slightly shorter than the full width, it helps to ensure that there is no binding that could lead to stress or damage to the glass or frame. Proper sizing contributes to the longevity and stability of the curtain wall system by accommodating movement and preventing potential deflection issues.

The choice of 1/16 inch strikes a balance between allowing for necessary adjustments and maintaining the structural integrity and tightness of the assembly. Other lengths, such as 1/8 inch, 1/4 inch, or 1/2 inch, would be excessive and could potentially lead to gaps or instability in the curtain wall system.