Design requirements for masonry veneers can be found in CSA S304-14 Design of Masonry Structures, Clause 9. Within the requirements, the Standard provides limits on both the unit material and unit dimensions (Clause 9.1.2) for Unit Masonry Veneer.

9.1.2  Unit material and dimension limitations

Unit masonry veneer shall be construction using clay (shale) masonry units, calcium silicate (sand-lime) masonry units, or concrete masonry units; the individual units shall be limited in height to not more than 200 mm, limited in length to not more than 400 mm, and limited in thickness to not less than 75 mm.
Note: Masonry units exceeding the specified maximum size limits may be considered to satisfy the requirements for unit masonry veneer, provided that independent testing confirms suitability for unit masonry construction methods, tolerances, and load transfer to structural backing.

The size limitations of masonry units have been harmonized throughout all of the material, construction, and design CSA Masonry Standards. Units within those size limitations are suitable for unit masonry construction methods and tolerances due to the extensive research and field experience that has been conducted on units within this size range as well as decades of satisfactory performance of structures featuring these materials. Units exceeding these size limitations are not covered by the standards and therefore the minimum requirements, performance, and tolerances may not be applicable.

Manufacturers are responsible for providing adequate testing to ensure that units which exceed the dimensional limits to unit masonry may still be designed and installed using masonry CSA standards. Test data, analysis, and relevant specifications shall be provided to the designer and masonry contractor to confirm unit suitability for unit masonry construction methods, tolerances, and load transfer to structural backing. This article provides some of the possible issues that should be considered for testing but does not represent a comprehensive list.

Each masonry standard serves a specific purpose. More information about the landscape of masonry-related codes and standards is available here.

CSA A370-14 is a material standard. It provides material requirements for the manufacturing of masonry ties, anchors and fasteners (collectively termed connectors).

CSA A370-14 provides material properties such as minimum connector strength, maximum connector free play, and maximum spacing limits.

CSA A371-14 is a construction standard. It provides requirements for the construction of masonry.

CSA A371-14 outlines guidance for many different aspects of construction, including but not limited to the following: tolerances of construction, reinforcement cover and tying requirements, mortar and grout placement, and maximum spacing of ties.

The design of masonry ties are solely covered by the CSA S304-14. Masonry ties must be designed to transmit lateral loads applied to the veneer from wind or earthquakes, the design of the masonry ties is subject to material properties such as the strength of the tie, expected differential movement, and construction properties such as the material used for the back-up.

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:

1. The building must adhere to all of the requirements of Clause F.1.1. This includes restrictions on the height of the masonry and the seismic hazard index.
2. 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 are not permitted through Annex F and are required to be designed to satisfy the requirements of Clause 9 of CSA S304-14.
3. Only prescriptive connectors may be used with Annex F empirical design. CSA A370-14 by default requires connectors to be designed for factored loads according to the CSA S304-14. While CSA A370-14 does also provide manufacturing and design requirements for prescriptive ties, the use of these provisions are 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 with their spacing based on the factored load and the factored resistance of the tie. Maximum spacing requirements are provided by CSA A370-14 and CSA S304-14. These do not represent a conservative solution without accompanying engineering analysis. The intent of this maximum spacing requirement is to limit cracking of the masonry veneer and has no relevance to strength or performance of the tie itself.

It is important that the most recent editions of relevant CSA standards are referenced. In the case of uncertainty, one can find the relevant edition of the standard in the list of referenced documents accompanying the building code in effect for any specific area. For the current edition of the national model code, National Building Code of Canada 2015, the relevant editions of the CSA standards are circa 2014.

Clause 8.1 from CSA A371-14 states that wire used for bed joint reinforcing shall have a minimum diameter of 3.0 mm and a maximum diameter of half the joint thickness or 5 mm, whichever is less. In practice, there are two common diameter sizes for joint reinforcing, 3.65 mm (termed “regular”) or 4.76 mm (termed “heavy duty”). In most cases, regular 3.65 mm joint reinforcement is preferred and should be specified because it is easier to cut, install, and lay units on, compared to heavy duty bed joint wire reinforcement. Heavy duty wire is more difficult to work with on site due to its increased rigidity and increased thickness relative to the mortar joint size.

The size of bed joint wire reinforcement required depends on the design. In general, when bed joint wire reinforcement is needed for crack control (e.g., over very long lengths of wall between movement joints, around openings, or as required in stack or decorative pattern masonry) then regular (3.65 mm) size wire should be used. The need for heavy duty wire is typically a result of meeting prescriptive reinforcing ratios for seismic design requirements or resisting in-plane shear forces in loadbearing walls. Therefore, its use must be determined by the designer and detailed within the contract documents.

When specifying bed joint wire reinforcement for cored clay brick or unreinforced concrete block, truss-type bed joint wire may be used. Truss-type bed joint wire reinforcement is fabricated by securing the cross-rods between wires at an angle to form a truss. The cross-rods will interfere with any vertical reinforcing bar placement in the masonry because of how the cross-rod passes through the open cell (across the middle).

Specifying truss reinforcing in masonry walls that will also be vertically reinforced will create great difficulty in placing the vertical reinforcing. Typical masonry construction practice will have the vertical reinforcing bars placed after the wall is constructed. If there are diagonal cross wires present within the cells it will make the placement of this reinforcing extremely difficult and will likely push the placement of outside of its tolerance window. In some cases, contractors may cut the diagonal cross wires of truss joint reinforcement to facilitate the placement of vertical rebar. However, CMDC generally discourages that practice.

To avoid situations where the bed joint reinforcing will interfere with the vertical reinforcement, truss type bed joint reinforcing should not be specified with vertically reinforced walls.

There is no recognized structural difference between ladder- and truss-type bed joint wire reinforcement. Ladder-type bed joint wire reinforcement has the advantage of locating cross-rods perpendicular to the main reinforcing wires in the face shells. Therefore, cross-rods can be arranged so that they lie on, or close to, unit webs ensuring they do not interfere with vertical bar placement. To alleviate any possible conflicts on site, ladder-type bed joint wire reinforcement should always be used with concrete block masonry.

Since vertical reinforcing bars are not easily or typically placed in clay brick or 10 cm concrete block masonry units, truss-type bed joint wire reinforcement may be used. When hollow or semi-solid 15 cm, 20 cm, 25 cm, or 30 cm concrete block masonry units are used then only ladder-type bed joint wire reinforcement should be used. This is the safest approach because of the possibility for these units to contain vertical reinforcing bars, however, truss type joint reinforcement can be acceptable with these types of units when designed and constructed as unreinforced.

Other than for veneer applications, the vast majority of bed joint wire reinforcement used in masonry construction does not require any additional corrosion protection requirements (i.e., plain steel is acceptable and preferred).

Typical bed joint wire reinforcement assemblies (ladders and trusses) are manufactured to be 40 mm narrower than the actual unit width resulting in a mortar cover of 20 mm. CSA A371-14 provides cover requirements for all reinforcing in masonry elements. Except where required for veneer walls, single wythe exterior walls, foundation walls, or interior columns and beams, all reinforcing bars (20M and smaller, without corrosion protection) or bed joint wire reinforcement in masonry walls require only 20 mm of cover from the masonry surfaces.

Designers are reminded that concrete masonry walls (e.g., shear walls and partition walls) are considered to be “interior” when they are located on the inside face of the wall cavity behind the building envelope’s waterproof membrane. These walls are not considered to be exposed to any direct precipitation, or weather, as defined by CSA A371-14. Exceptions can be made, for instances, where masonry is used within certain industrial settings such as  a sewage treatment plant, or for other special cases such as for a decorative fountain or pool, etc. when corrosion resistance for interior walls becomes a concern. However, in most applications plain steel embedded with at least 20 mm of mortar cover is sufficient for corrosion protection of bed joint wire reinforcement.

In cases where bed joint wire reinforcement is required in masonry that is exposed to weather (single-wythe walls, veneer walls), or potentially corrosive environments (industrial settings), then CSA S304-14 Clause 4.11.3 requires that the joint reinforcement must have the same corrosion protection as required for ties in accordance with CSA A370-14. Where corrosion protection is required, it should be indicated in the project plans in accordance with the levels of corrosion protection described in CSA A370:

• Level 1: no corrosion protection (plain steel or mill galvanized)
• Level 2: hot-dip galvanized after fabrication (requirements, including coating thickness are indicated in CSA A370)
• Level 3: stainless steel (acceptable grades of stainless steel indicated in CSA A370)

Spacing requirements for bed joint wire reinforcement are determined by the designer. There is no one-size-fits all spacing requirement for bed joint wire reinforcement. Since it is most commonly required to meet a prescriptive area of reinforcement (e.g., crack control) or to resist in-plane shear forces (e.g., seismic), the size and spacing requirements for bed joint reinforcement are dependent on many possible factors.

Crack control in masonry can be achieved with bed joint wire reinforcement, most commonly in concrete brick and concrete block walls. In such cases, designers may refer to industry recommended guidelines for its use (click here to open in new browser tab) and the recommended methods to determine if and how much may be required. Typically, crack control in very long spans of masonry, or around openings, is achieved by providing a horizontal reinforcement ratio based on net wall area of approximately 0.002. Seismic design requirements for non-loadbearing and loadbearing masonry may also require prescriptive horizontal reinforcement ratios based on the gross wall area per CSA S304-14. However, prescriptive maximum spacing limits and minimum reinforcement ratios may also account for the presence of bond beams. Furthermore, loadbearing walls may be governed by the need for bed joint wire reinforcement to resist in-plane shear forces, which itself may present different prescriptive limits.

Spacing of bed joint wire reinforcement should not be left to the specifications; instead, it should be established during the design of the masonry elements and based on the requirements of CSA S304-14 and CSA A371-14. There are few cases, in addition to stack pattern masonry, where a common size or spacing across all walls is necessary or justified; however, in many cases bed joint wire reinforcement that is added to meet no other definable design objective rationally calculated represents an unnecessary added cost.