How can I approach designing a masonry veneer?
Designing masonry veneers involves careful consideration of various factors to ensure structural integrity, aesthetics, and performance. The requirements for masonry veneers will vary based on various aspects of the type of structure they are intended for. Different approaches to design are required, considering the project’s specific requirements. For instance, the design considerations for a veneer on a small residential building differ from those applicable to a high-rise office building. For the veneers of buildings that require engineering analysis, careful attention should be paid to the requirements applied, depending on the loading conditions and type of backup structure. Understanding the scope and limitations of the different design paths is important. While veneers on small residential buildings, designed according to Part 9 of the building code, are restricted to a height of 11 meters when constructed from the building foundation, masonry veneers subject to engineering design following the CSA S304 masonry standards are not bound by height limitations.
Conflicts occasionally arise due to a lack of clarity, errors, or omissions in masonry specifications related to masonry veneers. Take a look at our articles about masonry specifications for a detailed discussion, as well as recommendations, that can help avoid conflicts.
Masonry veneers under the scope of Part 9 of NBCC
The National Building Code of Canada 2015 provides prescriptive requirements for buildings under Part 9 Housing and Small Buildings. NBCC, Section 9.20, limits the height of masonry veneer walls constructed on the foundation walls to a maximum of 11 m.
The building code also specifically prescribes the type of masonry units and minimum dimensions, type of mortar, mortar mix, allowable support types, specific types of veneer ties and tie spacings, and specific building envelope requirements for moisture and thermal resistance. In the case of any deviation from those requirements, engineering design of the veneer on Part 4 Structural Design of the code is required (which refers to CSA S304 for masonry design).
Masonry veneers under the scope of Part 4 of NBCC
Masonry veneers designed in compliance with Part 4 of the National Building code must be designed using the CSA S304 Design of Masonry Structures standard. Designers may be able to choose between using either the main body of CSA S304 (Clauses 1 to 16) or using the Empirical Design methods in Annex F if the structure meets the strict criteria which permit empirical design.
Masonry veneers under the scope of CSA S304: Annex F
For a masonry building that qualifies for design using Annex F, the masonry veneer may be designed using empirical methods. To design masonry ties using Annex F there are several important things to consider:
- The building must adhere to all the requirements of Clause F.1.1. This includes restrictions on the height of the masonry and the seismic hazard index.
- Veneers must be supported by a structural backing of concrete or masonry and must have a slenderness ratio, kh/t, less than or equal to 20. Design of veneers on wood or steel stud back-up walls is not permitted through Annex F and is required to be designed to satisfy the requirements of Clause 9 of CSA S304-14.
- CSA A370-14 by default requires connectors to be designed for factored loads according to the CSA S304-14. While CSA A370-14 also provides manufacturing and design requirements for prescriptive ties, the use of these provisions is limited to the same criteria that also apply to empirical design (low seismicity, limited wind loads, reduced building height, etc.). Prescriptive connectors must also be spaced at no more than the maximum spacing limits provided in Clause 10 of the CSA A370-14 as well as follow all of the requirements listed in CSA A370 for the specific connector used.
For cases where Annex F does not apply, ties for the masonry veneer must be designed according to Clause 9 of the CSA S304-14.
Masonry veneers under the scope of CSA S304: Clause 9
For masonry veneers according to Clause 9 of CSA S304-14, veneer ties must be designed to transfer the lateral load on the veneer (wind or earthquakes) to the structural backing. Their design is based on properties such as the strength of the tie, expected differential movement, and stiffness of the structural backing, to ensure the masonry veneer satisfies minimum requirements with respect to strength, serviceability, and resistance to moisture penetration.
Design of masonry veneers as specified in Clause 9 is limited to “unit masonry”, meaning that units must be no longer than 400 mm, no taller than 200 mm, and not less than 75 mm in thickness.
Clause 9 requirements offer designers considerable flexibility in their approach, provided that the structural supports for masonry veneers are designed to withstand applied loads and possess a stiffness compatible with the masonry. Additionally, attention must be given to addressing the effects of differential movements between the veneer and the structural backing, adjacent elements (whether structural or non-structural), and other rigidly attached components.
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