By: Mike Lopez
Most people understand the components of a building’s support system. Beams, columns and slabs create the basic framework for a building. But, a building also moves due to the fact that materials expand and contract.
A detail, known as the shelf angle, is commonly found in concrete framed buildings where there is a masonry or stone veneer that requires support. Typically, shelf angles are found at every floor level, and are comprised of steel “L” shaped angles. The angles are attached to the concrete frame of the building to support the masonry at that floor level; however, just as importantly, the angle provides a break in the veneer to allow for the expansion and contraction of the masonry and the concrete structure. Sometimes shelf angles are referred to as relieving angles; however, it is a common misconception that the term relieving angle refers to the angle providing relief to the masonry veneer. It would take a substantial amount of weight to cause a masonry wall to fail.
The most common issue we encounter with shelf angles is improper waterproofing detailing. The lack of waterproofing or insufficient waterproofing usually leads to deterioration and rusting of the steel. Necessary repairs may then include a substantial amount of brick removal/replacement, and sometimes steel replacement. These costly repairs exponentially raise the overall cost of a project.
Improper detailing as it relates to building movement can be another problem. As mentioned, building materials expand and contract. Proper detailing must account for each material expanding and contracting at a different rate. The steel of the shelf angle is attached/bolted to concrete. The concrete expands at a slower rate than the brick masonry the shelf angle is supporting. As a result, brick displacement and cracking can occur if the detail is incorrect. Repair details must include installation of an adequate expansion joint beneath the shelf angle that provides a cushion to absorb this expansion and contraction. Repairs can be costly and sometimes repetitive if the proper detail is not in place.
Application of sealant over the entire shelf angle joint is another common example of improper detailing. While water will not be able to infiltrate at the joint, any water entering from above the shelf angle joint will not be able to properly weep out, or in other words, exit the facade. This almost always results in rusting and deterioration of the shelf angle joint. Owners and Building Managers should reconsider this repair recommendation.
The shelf angle detail may appear to be a small aspect of the entire restoration project. However, if designed or installed incorrectly, it can lead to serious long-term deterioration of building components and materials, and negatively impact construction budgets.