Scuppers are very problematical in construction. If not properly designed and isntalled they can serve as a conduit for water to get into a building as much as to get off of a building. Scuppers are those small openings in exterior walls that allow water from roofs or decks to drain off through a guard wall or parapet. They are typically made of small sections of sheet metal tubing, like "drain pipe'. They usually protrude from a stucco or wood balcony wall, or roof parapet wall, for about three inches. Figure 8-2 shows a typical defective scupper installation in residential construction. While their purpose is to drain water to the outside, the way they are typically installed actually allows water to drain INTO construction. This ironic turn-about in multifamily construction causes homeowner associations to unnecessarily spend a great deal of money in premature repair of roofs, decks, rotted wood framing, and other components.

Scuppers are actually openings in the weather-resistive barrier. Their intended purpose is to serve as a conduit through this weather-resistive barrier for rainwater to pass from a roof or deck to the outside of the wall. While most scuppers function successfully in this manner, scuppers in residential and condominium construction also serve as a conduit for water to get back into the interior, by travelling back along the outer surface of the sheet metal tube, where it passes throught the weather-resistive barrier. This is possible because the metal tube is not sealed nor flashed against the passage of water from the outside back into the wall. Caulking the joint between the scupper and the stucco or wood that surrounds it is not an effective seal.
Water also can travel back into the wall along the bottom of the scupper, similar to what happens when a partially filled drinking glass is slowly tipped on its side. Section 1707 of the Uniform Building Code requires that the weather-resistive barrier be installed or applied "free from holes and breaks other than those created by fasteners and construction system due to attaching of the the building paper." When residential scuppers are installed in walls, holes are cut into the weather-resistive barrier for the scupper to go through, and these holes are left un flashed and unsealed.
Each such hole allows for water penetration, which can create rot and mildew, and destroy deck and roof membranes.
The required method of installation of the weather-resistive barrier is "weatherboard fashion," indicating the lengths of the building paper are put up on the wall beginning at the bottom in the same nature that weatherboard paper are put up on the wall beginning at the bottom in the same nature that weatherboard siding is applied to the wall: from bottom to top in each succeeding weatherboard lapping the top of the preceding weatherboard. Flanges around components that penetrate the weather-resistive barrier, such as windows, vents, and scuppers, must be "shingled-in" to the barrier in the same method. This will insure that water running down the wall, or out through the scupper, always drains to the outside of the wall surfaces, never getting inside the construction.
To be installed correctly, scuppers should be installed like little windows, with flanges all around, properly flashed so water cannot travel back behind the weather barrier using the scupper itself as a conduit. Unfortunately, this requires more time and effort than the usual installation, and is therefore almost never done. The installation of scuppers in construction without flanges flashed into the weather-resistive barrier "shingle fashion" or, "weatherboard fashion" is sure to result in problems.
Homeowners, directors, and property managers can eliminate or reduce damage to their property from improperly-installed scuppers by inspecting their installations, and taking appropriate preventive measures. Check around the scupper as it protrudes from the wall. Often there are openings of 1/4" to 1/2" between the stucco or wood and the scupper. This is where the water gets in. Sometimes the space is tightly closed, with the stucco snug against the sheet metal. No matter; even a hairline crack between the two lets water in. Preventive measures include the injection of fungicide-preservative into the space around the scupper, where water is likely gaining entry. A borate-based preservative is best because the borates kill any fungus presently growing in the wood framing, and remain "on the job" for many years to come to eliminate any new fungus from taking up residence.
A good retrofit of a defective scupper is to remove the stucco, brick, or siding around the scupper for about 6" all around, and fit a sheet metal rain color over the scupper. The rain collar should have a 3" flange on the top and on both sides, similar to the nailing flanges of a window with corners soldered, and a section to completely cover the scupper top and both sides. It should be installed against the weather-resistive barrier with its flanges properly shingled into the weather-resistive barrier as in the fashion of windows.
Although the proper correction requires the fitting of a flanged collar against the weather-barrier, a less effective, less costly alternative is to fit the scupper instead with a collar that can be sealed against the outside of the wall and the scupper itself, to prohibit the further entry of any water. The seal should not be an inexpensive caulking application, but should be a permanent sealant with a properly formed and prepared joint. Finally, the supper discharge itself must be modified to incorporate a "drip," a down-turned lip at the lower outside end of the tube. This will eliminate the possibility of water passing through the scupper from running back into the wall along the bottom of the tube itself.
Connell, Scuppers Let Water In, Condo Management, California, (November 1995).

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