Figure 1. The existing foundation must be wide enough to support at least two-thirds the thickness of the new veneer. Otherwise, an extended footing (pictured above) or steel-angle support (Figure 2) will be required.
Illustration: Brick Industry Association
1 Make sure the brick wall is on a sound footing. Although brick veneer is a non-load-bearing component, the weight of the veneer must have foundation support. If the existing foundation is not wide enough to accommodate the veneer (the foundation must support at least two-thirds the thickness of the new veneer), there are two options: pour an extended footing (Figure 1) or provide steel-angle support anchored to the existing foundation wall (Figure 2).
When pouring an extended footing, Trimble recommends that a bond break material, such as flashing or building felt, be placed between the existing foundation and the new footing to allow for expected differential movements between the concrete and brick.
The steel-angle support method is not recommended for multistory structures or for brick veneers that exceed 12 feet in height. When using this approach, make sure to specify corrosion-resistant steel angles, and, if possible, design the detail such that the horizontal leg of the angle is at or slightly above grade so as to keep frost heave of the soil from impacting the veneer support.
|Figure 2 illustrates a steel-angle support anchored to an existing foundation wall. This approach can be used to support a new brick veneer. Illustration: Brick Industry Association|
If the angle must be placed below grade, the space beneath the angle can be backfilled with freely draining granular material surrounded by a geotextile and a compressible pad to protect the angle from displacement. Angles can be attached to the foundation wall using either mechanical anchors or through-bolts. When through-bolting, seal the annular space around the shaft of the bolt to prevent water penetration.
2 Make sure the existing building has a continuous water barrier. Inspect and repair the existing siding as necessary to act as a water-resistive barrier. If the existing siding cannot be readily repaired, wrap it with a new water-resistive barrier. If neither of these options is desired, remove the existing siding and inspect and repair the existing water-resistive barrier and sheathing as necessary. Install a new water-resistive barrier where none currently exists. Existing sheathing should not be used alone as the water-resistive barrier. “In many retrofits increased insulation levels are desired, so removing the old siding and placing rigid insulation in its place is an easy idea,” says Trimble.
3 Don't skimp on the drainage wall details. Provide details in accordance with BIA Technical Note 7, materials in accordance with Technical Note 7A, and workmanship in accordance with Technical Note 7B. “The most important details are around windows and other features such as bay windows,” says Trimble. “Flashing at the window heads and sills is critical for performance in this new veneer.”
4 Provide at least one inch of air space behind brick veneer. This gap functions as the drainage cavity where water is directed downward to the flashing and weeps and out of the brick veneer. If open weeps are used, this air space also helps to vent the cavity, allowing things to dry out quicker, says Trimble.
5 Get anchor spacing right when attaching the veneer to the existing wall. The brick veneer must be securely attached to the existing construction throughout its height. When using adjustable two-piece W 1.7 (MW11) wire or 22-gauge corrugated anchors, provide one anchor for each 2.67 sf of wall area. For other anchor types, provide one anchor for each 3.5 sf of wall area. The maximum spacing of anchors cannot exceed 32 inches horizontally or 18 inches vertically for nonresidential construction.
“Corrugated ties are limited to use with one inch of air space, so if the air space is wider than one inch, use a wire tie,” says Trimble.
6 Flashing is critical. In order to divert the moisture out of the air space through the weeps, install continuous flashing at the bottom of the air space and above grade. Where the veneer continues below grade, completely fill the space between the veneer and the existing construction below the flashing with mortar or grout.
Install flashing at the heads and sills of all openings and wherever the air space is interrupted. Turn the back of the flashing up a minimum of eight inches such that the top edge of the flashing is covered by or sealed to the existing siding. The front edge of the flashing should extend to the face of the brick veneer. Where the flashing is not continuous, such as at heads and sills, the ends should be turned up about one inch to form an end dam.
7 Make sure weeps aren't too far apart. Locate weeps in the head joints immediately above all flashing. The maximum recommended spacing of open head-joint or vent-type weeps is 24 inches on center. When wick materials are used in the weeps, the maximum recommended spacing of weeps is 16 inches on center. “The use of weeps is not rocket science,” says Trimble. “Whatever gets the water out of the wall the quickest is the best approach.”
8 Maintain proper clearance at the top of the veneer. Allow for a minimum ¾-inch clear space between the top of the last course of brick and the bottom of the existing soffit. Bridge the gap with a new molding strip and sealant to protect the wall from moisture intrusion. If the existing eave is insufficient to fully cover the top of the veneer, extend it to protect the top of the brick veneer.
9 Watch out for movement on taller elevations. Since brick grows over time and wood typically shrinks, these differential movements should be taken into account. The movements are ordinarily insufficient in small brick veneer buildings. However, larger structures (taller and longer) may require expansion joints, flexible anchorage, joint reinforcement, bond breaks, sealants, or other design details to accommodate potential differential movements, especially around existing second-story windows.
“At higher elevations, the amount of movement adds up over the height of the wall,” says Trimble. “More space is needed around windows to allow brick's natural growth to occur. Placing a larger sealant joint, say greater than a half inch, may be all that's needed.”
For more on re-cladding with brick, download BIA's Technical Note 28A at www.gobrick.com . —Dave Barista, Managing Editor