During the late 1990s, a leading masonry expert attributed the deaths of 30 people and injuries to 81 others to 49 incidents involving falling masonry from unsafe façades. The late forensic engineer Tom Grimm noted in the March 2000 issue of The Construction Specifier, that masonry was falling from a building façade somewhere in the U.S. about every three weeks. Grimm then urged the masonry community to adopt new anchorage devices, materials, and designs to mitigate the serious problem.
To architects, concern for a building's façade involves its exterior exposure. They view the presentation of the windows, doors, metal railings, coatings (such as stucco), or coverings as the image the building owner wants to express to the world. But to the mason contractor, the performance of the non-structural elements of the masonry covering, including stone, brick, terra cotta, and cast stone, should be approached as anchored veneer.
The masonry community has responded pro-actively to this serious problem in the last decade. Spurred by a series of municipal code enactments that required periodic inspections of building exteriors, mason contractors now have a host of efficient forensic equipment, durable repair materials, and sturdy anchorage devices to help ensure long-term veneer wall integrity. As the recent seismic tests on masonry veneers conducted last summer in San Diego demonstrated, when code guidelines are followed in anchorage design and material selection, veneer on walls performs safely (MASONRY CONSTRUCTION, May 2009).
Many of these improvements are based on recommendations from investigations of the late 1990s. Due to the cyclical and conservative nature of building codes, many of these improvements are now finding their way into the various masonry construction codes and guidelines that cover façade repair. For contractors wanting to be a part of this growing industry segment, it's important to stay abreast of what is happening.
As always, the best place to start is by reviewing the current Building Code Requirements and Specifications for Masonry Structures. One of the topics in the report by the Masonry Standards Joint Commission (MSJC) is anchorage, specifically for veneer. Currently published on a three-year cycle, many municipalities are updating their masonry construction standards by referencing the 2008 MSJC Code edition. (The MSJC code document does cover installing dimension stone.)
Defining masonry veneer
The 2008 MSJC Code defines masonry veneer as "a masonry wythe that provides the exterior finish of a wall system and transfers out-of-plane load directly to a backing, but is not considered to add load resisting capacity to the wall systems." When brick, cast stone, or stone façade is constructed as a wythe, its design should conform with Chapter 6 of the MSJC code.
This information provides engineers and contractors guides regarding designing and detailing anchored masonry veneer. Specifically, Section 184.108.40.206 provides current anchor requirements for veneer masonry. Contractors should note that this is a change from previous MSJC code documents.
In reviewing concrete documents that pertain to façade repair, contractors should pay close attention to use the words tie and anchor. The MSJC 2008 code defines wall ties as "metal connectors that connect wythes of masonry walls together."
In the commentary section, the authors provide guidance on this important concept. They agree that veneer anchors could be considered to be ties. But they point out that using the term anchor regarding veneers has become common in model building codes. They suggest veneer anchor better describes the devices specifically designed to perform this reinforcement.
The authors say this distinction is needed as veneer anchors often allow movement of the veneer section in the vertical plane. Yet these anchors resist movement perpendicular from the plane, or away from the structural wall or stud. Since anchor manufacturers provide data outlining test results for stiffness and strength for their proprietary units, contractors should check materials for each job.