Four Ways to Create a Better Building
You can create a better buildings through the implementation of compatible materials.
The walls of today’s masonry buildings are becoming more complex than ever as designs are modified to meet new energy code requirements. These modifications require more components in walls than in the past, and these components can come from different manufacturers.
A basic masonry cavity wall is simply two wythes of masonry separated by a space or cavity of varying dimensions. Masonry is among the most ancient of building materials, but until fairly recently, masonry walls were solid masonry with no cavity between the inner and outer wythes. Also called “barrier walls,” solid masonry walls were the only types that could be built at one point, due to limitations of materials manufacturing and building technology. Barrier walls relied on sheer mass to provide structural strength, resistance to heat transfer and water infiltration protection.
Now, designers must choose from a wide variety of materials to specify a sustainable wall that meets today’s exacting energy codes. All of the materials must perform together, although they are made by a differing manufacturers who may not test their products for compatibility with other companies’ products.
Let’s shed some light on which of the most commonly used materials are compatible from both a materials composition and functionality standpoint, as well as which should never be used together.
Bricks and mortar
The bricks and mortar of the outer wythe must be matched to provide a look that coincides with the designer’s vision, plus a combined compressive strength that supports the weight of the wall and any other materials attached to it. Bricks are locally manufactured, so brick appearance and strength will vary depending on the raw materials used and each manufacturer’s individual processes. Standard clay bricks and lightweight bricks using materials such as fly ash are available. Please consult your local brick manufacturer to determine the right type of brick to specify for each job.
Brick ties and stone anchors
A variety of ties are available for cavity walls to link the outer wythe to the structural wall. The most effective are three-part systems that consist of a barrel that has been engineered specifically for the cavity width, with a screw designed to penetrate the specified structural backup wall. Examples of this include concrete masonry units (CMUs), or steel or wood studs with sheathing; a plastic clip that acts as both a thermal break and a dissimilar metals break; and the wire tie, which can be hot-dip galvanized or stainless steel.
Stone anchors must be custom manufactured and typically are made from stainless steel to avoid galvanic responses between the ties and minerals in the natural stone. Cast stone, which is actually concrete, does not require stainless steel. However, given the small cost difference relative to the cost of anchor failure, stainless is the better choice, since it eliminates compatibility problems.
Ladder-type or truss-type horizontal joint reinforcement is used in CMU structural walls to provide lateral stability. Truss-type reinforcement may be incompatible with CMU walls with full or partially grouted cells, not because of a materials issue, but because the cross wires can interfere with vertical rebar placement and grout flow. Minimum wire thickness is 9 gage or .1483 inches, and mortar bed thickness must be at least twice the thickness of the embedded wire.
Assure you specify stainless steel, hot-dip galvanized after fabrication or epoxy-coated wire to avoid in-wall corrosion. Ladder-type wire reinforcement may be formed in a way that spans the cavity, either with solid wire or with eyes designed for use with separate pintles, so it acts as both CMU reinforcement and a brick tie. It is highly recommended that ladder-type wire reinforcement that does not extend past the exterior of the CMU backup wall be used in combination with the separate brick anchors described above. This allows greater movement in the wall and provides an effective thermal break.
Airtight and watertight washers
For maximum energy efficiency, use 2-inch diameter plastic washers with the brick tie barrel anchors when they are penetrating RI in the cavity. This helps to seal out air and moisture while permanently attaching the insulation. One manufacturer’s washers also have pre-spotting prongs that embed into the insulation for easy on-the-wall veneer anchor assembly and attachment through the RI and into the substrate. Two manufacturers of washers, ties and fasteners have tested their products to be compatible and are also components in a complete wall system. This means that all components, including WRB, mortar dropping collector, wall flashing, pre-formed corners and end dams, and weep vents are proven compatible and have passed NFPA 285.
With all the components available to the designer and builder in modern masonry cavity walls, it can be time consuming to process. But it is important to verify that all selected components are compatible for material performance and functionality, as well as with the environment in which they’re installed. Fortunately, manufacturers are offering tested wall systems in which multiple components have been proven compatible, making the designer’s job faster and less risky.