- Question: How far beyond the front edge of an angle can a brick unit project? What problems result if the horizontal leg of the angle is too short?
Answer: The angle should support 2/3 the thickness of the brick masonry veneer, according to the Brick Industry Association's Technical Note 28B.
The brick can fall off during construction if the angle does not support more than 1/2 of the units. These brick units can be temporarily supported at the outer edge off the top of the brick wall below during construction. This approach cannot be used at window lintels where there is nothing immediately below the outside edge of the brick to shim against.
Initially, when the mortar is still green, the units may rotate to maintain full contact with the angle. However, as the mortar begins to set the units no longer rotate to conform to the deflecting shape of the shelf angle. The shelf angle continues to deflect as more weight is added.
Even though this deflection is very small, it still causes the center of the reaction between the brick and the angle to shift closer to the back portion of the brick masonry. Therefore, even if the angle initially supports 2/3 of the brick, after construction only the back portion of the brick veneer may be effectively supported by the shelf angle.
Shelf angles should always be designed to handle at least 2/3 the depth of the masonry veneer to properly support the flashing and masonry during construction. If walls are built with less than 2/3 bearing, replacement of the angles may not be necessary. Unless other problems exist, the angles may be capable of supporting the masonry. In these cases a structural engineer should be hired to review the condition.