As a design professional, when it comes to anchoring systems for anchored masonry veneer, you may be inclined to simply leave it to the contractor to figure it out as a part of the means and methods of construction.
Understanding Anchored Masonry Veneer
While there is some truth to that, many architects and design professionals provide anchoring designs in their specifications and design details and also provide services during construction in which the anchoring systems may be open for observation and inspection, so a good understanding of how to properly anchor this type of veneer is definitely beneficial.
Masonry Veneer Types
First things first, masonry veneer has two primary types: anchored and adhered. Adhered masonry veneer is commonly known as “thin brick” or “thin stone” and is directly adhered to the underlying structural wall, be it a stud-framed wall, or solid concrete or CMU backing. Anchored veneer is that type of masonry veneer where the veneer units are secured and supported laterally across an air space/drainage cavity through anchors secured to the structural backing. Anchored veneer is also vertically supported by the foundation or other structural elements (steel angles, lintels, etc.).
The International Building Code (IBC) regulates exterior walls in chapter 14 and regulates wall coverings in section 1404 (2018 edition). Section 1404.6 regulates anchored masonry veneer, requiring conformance with certain provisions of The Masonry Society (TMS) document 402, which is titled “Building Code Requirements for Masonry Structures.” It’s really easy to skip over that small section of the code as it’s less than one sentence, but it’s very important that you understand what’s in the TMS 402 document, as it provides the rules related to prescriptive anchored masonry design.
TMS Document 402: Building Code Requirements for Masonry Structures
TMS 402 offers two options for the design of anchored masonry veneer: prescriptive or rational (engineered). Prescriptive design is generally going to be easier if your project can accommodate standard masonry construction, as the prescriptive rules are all laid out in the TMS 402 document, and all you have to do is “do it by the book” and make sure your details and specs match the prescriptive rules in the code. Alternatively, if your masonry design falls outside of the parameters of prescriptive design, an engineered design is required to make sure the veneer is properly attached to the underlying structure. If your design cannot accommodate prescriptive veneer attachment for any reason, an engineered solution is required.
Veneer System Backing
TMS 402 regulates, among other things, the “backing” of the veneer system. The term “backing” is specially defined as the wall or surface to which the veneer is attached. Throughout the TMS 402 standard, prescriptively speaking, the backing can be one of four options: wood studs, metal studs, solid concrete, or a CMU wall. This should cover most of the common types of construction nowadays, but if your building features a different exterior wall system, the prescriptive standards may not apply and an engineered design would be required.
Veneer System Anchors
TMS 402 also regulates the types of anchors/ties that are to be used for the veneer. These anchors include corrugated metal ties, wire anchors, adjustable anchors, and others. The spacing requirements for each type of anchor are also noted, with limitations on maximum spacing in the field of the wall, and requirements for additional anchors around openings in exterior walls (doors, windows, etc.). When it comes to things like anchor spacing, if the structural backing is a stud-framed wall, it can be important to make sure the anchor spacing is compliant with the stud wall spacing. For example, if the maximum allowable spacing for a masonry anchor is 32″ o.c. horizontally, and your walls are framed at 24″ o.c., then your anchor spacing will have to be 24″ o.c., and cannot be 32″ o.c. because the studs don’t line up. Also keep in mind the project’s wind zone, as high wind zones (hurricane zones, etc.) will require tighter anchor spacing, and may fall outside of prescriptive standards entirely for extremely high wind areas.
As to openings, this standard requires additional anchors around the perimeter of the openings, with anchors required within 12″ of the opening. If you’re providing construction observations or inspections, it might be a good idea to understand these special requirements so you can verify if the construction is being done per code or not.
Ultimately, as a design professional, the TMS 402 document is important for you to have and understand, so your designs can properly match the requirements of the code in this regard, and so you understand when prescriptive design cannot be achieved and an engineered design is required. Even though it may be tempting to just leave this to the contractor, you’ll be a better design professional if you understand and can speak to this aspect of building design and construction with knowledge.