Walls & Ceilings Architect/October 2007

the FINISH LINE BY ROBERT THOMAS can make the sofﬁt ﬂutter, leading to cracking. Sometimes bracing may be needed to avoid this. FIRE Stucco is completely inorganic and is therefore noncombustible. This means it can be used on any building type, and also can provide some ﬁ re resistance. EIFS is not noncombustible and special ﬁ re tests are required by code to conﬁ rm the performance. Some EIFS products are for residential (combustible) construction only for this reason. For EIFS-clad walls, the hourly ﬁ re resistance rating for the whole wall comes completely from the supporting wall; the EIFS does not add to the rating. Stucco to EIFS It’s no wonder that EIFS is sometimes called “synthetic stucco.” Sometimes it’s hard to tell one from another until you touch the wall, especially if an EIFS ﬁnish is used over the stucco as the ﬁnal coat. It’s quite common for EIFS projects to be changed to stucco, and vice versa. Since the two claddings are so different in their characteristics, it’s not a simple matter of just making the switch. This month’s column gives you a checklist of things to keep in mind if someone wants an alternate price or prefers the other cladding. This list will be handy if you are working with a designer or owner who needs guidance when making a switch. First, in terms of discussing EIFS vs. stucco, lets deﬁ ne “EIFS” thusly: The attachment system plus the insulation plus the base coat (adhesive and mesh) plus the ﬁ nish. Then let’s call the “stucco” the scratch coat plus the brown coat plus some type of ﬁ nish, in other words, traditional exterior Portland cement 3-coat plaster. Then, let’s consider the substrate (the supporting wall) separately, as it can take many forms and may, or may not, include a variety of other materials such as manner of sheathing, building paper, water barriers, and so on. Changing THICKNESS Stucco is about 3/4-inch thick. EIFS is at least 3/4-inch and can get up to 4 inches or more. When changing claddings, make sure to check the perimeter of the system. This includes openings, windows, ﬂashings, doors, penetrations, railings, and so on. The thickness change may require re-detailing these areas, such as the need for flashings when none were used before. Windows can be a special problem, especially if thick EIFS “returns” into the edge of the opening, and with windows that swing out. WEIGHT EIFS weighs less than 1 pound per square foot. This makes it one of the lightest claddings available. Stucco weighs about 10 times as much. Neither is a super heavy material (like thick precast concrete), so this difference sometimes doesn’t matter in terms of the design of the supporting wall. But sometimes it does. If the whole building needs to be light in weight—such as a building at a marina that is built on pilings, or prefab panels that are to be lifted by a helicopter, or an addition on top of an existing building—then this difference can be important. The key is to be sure that the substrate, especially if it is light gage framing and sheathing, can handle the weight. This means especially checking the sheathing-tostud fastener capacity. It’s also important in inverted application (sofﬁts). Sometimes sofﬁts are hung from wire and channel iron, and wind uplight STIFFNESS AND DEFLECTION Stucco is a rigid brittle material, and if overﬂexed, can crack. EIFS is ﬂexible and can withstand a lot of bending. Thus, if changing from EIFS to stucco, check the deﬂ ection of the studs. For stucco the studs may have to be beefed up to make them stiffer. The stiffness of the supporting stud framing is especially important with prefabricated panels. Sometimes the stresses that the panels are subject to during lifting and transporting are higher than those exerted by the wind once on the building. This can result in the panel frame needing to be made of considerably thicker or deeper studs, or extra bracing for stucco panels so that the panel does not sag, rack or torque too much when being handled. 36 | Walls & Ceilings Architect | October 2007

Table of Contents Feed for the Digital Edition of Walls & Ceilings Architect/October 2007

Contents Trade News Silver Certiﬁed Airtight The Men of Steel Thinking Thermal Firestop 101 ICFs Create a Tight Envelope The Finish Line The Green Thumb Cracking the Code

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