Code Requirements for Anchoring Masonry Veneers
Add quality and prevent failure by recognizing errors.
By Jeremy Douglas
Last week, on a project site, I was asked to look over air barrier detailing and flashing installations. As I glanced across the wall, it was obvious that the anchorage fastened into the steel stud backing was too far apart. My initial reaction, thinking the worst, was to ask the contractor why he was choosing to space the anchors so far apart. When we went to the trailer and pulled out the pile of drawings, I learned immediately that I was wrong. The drawings indicated inadequate spacing. Since drawings can be incorrect, all mason contractors should know and understand masonry code requirements for anchoring masonry veneers.
TMS-402 Building Code Requirements for Masonry Structures (formerly known as ACI-530) is maintained by The Masonry Society. It is the Code of Reference for the masonry sections of the Residential and International Building Codes. Pertinent requirements for anchoring masonry veneers in typical wall conditions with common two-piece systems include:
- Minimum air space of 1 inch in a veneer assembly. While this may not be directly related to anchor systems, it is relevant to the overall size of the tie system used. While 1 inch is a minimum requirement, it should be noted that a larger air space is desired to improve ventilation within the cavity and to make laying brick substantially easier.
- Any span of cavity greater than 4½ inches requires an engineering analysis. This span is measured from the back of the veneer to the face of the block or concrete if a masonry backup wall is used or to the face of the stud if a CFM stud or wood framed wall is used. This span will likely become larger in future codes, provided that the anchors used meet certain physical and performance criteria.
- Veneer anchors require a minimum embedment depth of 1½ inches to the bed joint. Measure carefully when integrating continuous wire in the veneer; while you are required to maintain this minimum embedment depth, you also are required to provide a minimum of 5/8 inch of mortar cover of those anchoring components to the exterior face of the bed joint.
- All embedded anchoring components must be sized no greater than one-half the thickness of the mortar joint. Most veneer ties are manufactured with 3/16-inch wire to comply with this requirement, though ties engineered for special conditions or higher strength will need to be specially formed where embedment occurs in order to be used with standard 3/8-inch mortar joints.
- All two-piece anchoring systems must have no more than 1/16 inch of clearance between parts. These connections must be tight. Do not mix components from different manufacturers.
- Anchor systems in walls exposed to weather, earth or an average relative humidity equal to or greater than 75 percent must have a hot-dipped galvanizing finish, be epoxy coated or made from stainless steel. Mill galvanized components should be used in low-humidity interior walls only. Also, any stainless steel components should be of a 304 grade stainless in standard wall conditions, or a 316 grade if being used in particularly wet conditions or salt-air environments.
- Under ordinary conditions, anchors are to be spaced no greater than 32 inches horizontally, with a maximum vertical spacing of 25 inches. These spacings are often narrowed by special conditions, such as seismic requirements, wind load analysis, wall height, or cavity spans. Manufacturers may recommend limited spacing on particular anchors because of load capacity of a particular anchor. Also, openings greater than 16 inches require anchors be placed within 12 inches of the perimeter. Anchor spacings will usually be reduced at the corners, as well, to accommodate higher wind loads.
Additional building code requirements exist when using a corrugated wall tie to anchor a masonry veneer, which has rendered these types of anchors impractical to use in most modern construction. First, the wall configuration must include both a minimum and a maximum of a 1-inch air space between the back of the veneer and the face of the sheathing. This means it is not possible to use any type of exterior continuous insulation with these ties. All corrugated ties are required to be a minimum of 22 gauge in thickness and 7/8 inch in width.
While 28-gauge corrugated ties are readily available in masonry yards all over the country, they are not permitted by code. Corrugated ties also are only permitted to be fastened to wood backing, and the fasteners used must be located within ½ inch of the 90-degree bend. If you use these types of ties regularly, be sure you’re meeting these requirements for anchoring masonry veneers.
If you do not have a copy of the code including the requirements for anchoring masonry veneers, this information is easily accessible from groups such as International Masonry Institute (IMI, http://imiweb.org) or Brick Industry Association (BIA, GoBrick.com).
As an installer of these anchoring components, you are not only the last line of quality control for the veneer system, you also have an opportunity to prevent potential failure within your brickwork – and, more important, an unforeseen callback later down the road. Being recognized as an industry professional who has a solid understanding of his craft, as opposed to being perceived as a contractor who simply follows a bad plan as drawn, is an added benefit.
Jeremy Douglas, CSI, CCPR, is the director of architectural services for Hohmann & Barnard. He serves as the primary technical resource to the design community and has written dozens of seminars and technical resources on the subjects of moisture control, building envelope systems, reinforcing and anchoring and masonry restoration.