Scuppers are drains that penetrate through walls. They are used on decks, balconies, parapets and roofs to allow for the removal of excess water and to keep it from pooling in one space, where it may cause damage. If an exterior area like a deck has Exterior Insulation Finish Systems on both sides, the scupper will be put through the base of the walls to allow the water to leave the area.
Scuppers are very prone to leaking and allowing water intrusion into the wall if they're not installed properly. Basically, they are a large opening in an exterior wall for water to run out of, approximately four inches across and four inches wide, made of metal tubing. Scuppers can be difficult to install with EIFS, because scupper flashings are relatively complex and don't attach to the coatings on the EIFS very well, and an improperly installed scupper will direct water into EIFS, not away from it. This will lead to many structural integrity issues as well as the regular mould and rot associated with water intrusion. Caulking the area where the scupper tubing meets the exterior wall is also not an appropriate seal, and it won't hold up to the requirements that are needed of the drainage. The best way to properly incorporate a scupper flashing into EIFS is to not have the EIFS terminate below the deck, and this way the scupper flashing can be adhered to the deck coatings themselves, instead to to the EIFS coatings.
Scuppers are usually a secondary source of drainage, to be used as overflow protection in the case of the primary drainage source being clogged or unusable. If used on a deck, for example, the deck should be sloped in such a way that any water will automatically be directed to the main drain instead of the scupper. Because decks are usually flat and don't slope, the water and any grime along with it will head for the scupper and stain the EIFS wall on the other side. The scupper should be designed so it carries the water at least three inches past the EIFS on the other side, to prevent this staining.
If one were to fill up a drinking glass with water and slowly tip it until the water begins dribbling out, the water does not flow out of the top of the glass cleanly. It runs back down the bottom the glass and onto your hand. This is what happens with improperly installed scuppers, as they provide a conduit for water to ride back on and into the wall. Along with carrying the water at least three inches past the wall to drain, the scupper should have a drip edge to keep the water from dripping back down the base of it.
If the scupper is placed an inch above the surface of the deck, the water on the deck won't drain until there's more than an inch of it pooled there. The base of the scupper should be at least flush with the surface of the deck, if not lower.
Architects planning on using scuppers in their designs should consult with the EIFS installer or the EIFS manufacturer to fully understand the design of a properly installed scupper and to incorporate it as such into their plans. This will also prove helpful because proper scupper installation involves cooperation between many different parties involved in the overall construction, such as the deck builders and the EIFS installers.