Q: Why are corrugated wall ties permitted in brick veneer walls with wood stud back-ups, but not in brick veneer walls with steel stud backup walls?
A: Metal anchors are used in masonry veneer walls to transfer lateral loads from the veneer to the backup wall. In most areas of the country, design wind loads are greater than design seismic loads. Corrugated anchors generally have lower capacity than other types of masonry veneer anchors. However, the reason that they are permitted for wood stud backups and not for steel stud backups is related more to historical usage than it is to engineering. Corrugated wall anchors have been used for decades with limited failures. However, engineering calculations often show that these anchors do not have sufficient capacity without excessive movement.
Their low rate of failure is probably related to the fact that these systems are typically used in residential construction. Exterior brick veneers in residences often have many corners and offsets. These features strengthen the veneer. As a result, the masonry veneer in many cases can safely handle wind loads without significant contribution from the backup wall. Since building codes limit brick veneer with wood frame construction to three stories in height, the wind loads are also significantly less than those in taller buildings.
Although corrugated anchors are allowed for wood frame structures, the ultimate responsibility regarding the appropriate anchor belongs with the designer or contractor. The Brick Industry Association's Technical Note 28 states that “the ties must be capable of resisting tension and compression resulting from forces perpendicular to the plane of the wall.”
Consider the application before using corrugated anchors. If the residence has large, tall walls with very few corners or offset areas that could stiffen the wall, or if the residence is located in an open area, consider engineering wall anchors to resist lateral load rather than relying on prescriptive code requirements. Consider using air spaces wider than one inch, since wider air spaces reduce the risk of mortar bridges; with wider air spaces, corrugated anchors are not permitted. When corrugated anchors are used, they should typically be bent at the fastener to increase capacity and greatly reduce flexibility, screws should be considered for fastening the anchor to the studs instead of nails, and additional anchors should also be added at the tops of walls.