Replacing flashing

Q: My company is currently replacing the flashing on a building because of leakage problems. We are taking out alternate sections about 4-ft long and replacing the veneer in these areas before removing the masonry adjacent to it. This approach is being used to support the masonry during the flashing repair. Unfortunately, this plan results in splice joints in the flashings every 4 ft or so.

What is the maximum length that can be taken out?

A: The maximum length that can be removed without impacting the masonry above depends on many factors, such as location of expansion joints, height of the wall, and condition of the masonry. The veneer must span between the alternating piers of masonry. Any expansion joints located within the region between the piers prevent arching of the masonry from occurring.

In these cases, only a small amount should be taken out on either side of the expansion joints so that the masonry can cantilever from each of these piers rather than spanning or arching between them. The length of the span needs to be determined based on the conditions observed at cracked or deteriorated masonry.

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A rule of thumb is to limit the length of the opening in the masonry based on the height of the remaining portion above. At masonry spandrel areas between horizontal strips of windows, the length of the masonry removed can be very small using this rule.

In most cases, when performing flashing repairs the contractor opts to provide some method of supporting the masonry above so that the whole length of flashings can be replaced at once. This technique greatly limits the number of joints in the flashing and simplifies observation of the installation as part of a quality assurance program.

In many cases with older buildings, the shelf angles or lintels are replaced in conjunction with flashing repairs. Supporting the masonry above long openings also permits these angles to be replaced.

There are many ways to support the masonry in these cases. When there is a concrete beam behind the masonry, it is typically possible to use shear pins to support the masonry above the opening, Fig. 1. When shear pins are used, it is often desirable to install them at an upward angle, Fig. 2. By installing the shear pins at an upward angle, chips or other small damage that may occur to the brick during the installation of the pin are found in the back portion of the piece.

Small chips on the interior face of the wythe typically would not require that the brick be replaced. Shims can be installed between the pin and brick above to help support the masonry.

Where there is not a large concrete beam to insert shear pins, special steel brackets can be fabricated and installed to transfer the weight to the masonry below. These brackets can be made of threaded rods and angles when there is limited masonry above the opening, Fig. 3.

If the weight of masonry is greater, a vertical angle may be needed instead of threaded rods to handle the higher loads. The vertical member of the bracket that extends across the opening needs to be about 1 cm. in front of the surface of the masonry to facilitate installation of metal drip edges and other types of flashings.