The Finish Line: Changing Stucco to EIFS
August 24, 2007
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 define “EIFS” thusly: The attachment system plus the insulation plus the base coat (adhesive and mesh) plus the finish.
Then let’s call the “stucco” the scratch coat plus the brown coat plus some type of finish, 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.
WeightEIFS 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-to-stud fastener capacity. It’s also important in inverted application (soffits). Sometimes soffits are hung from wire and channel iron, and wind uplight can make the soffit flutter, leading to cracking. Sometimes bracing may be needed to avoid this.
FireStucco is completely inorganic and is therefore noncombustible. This means it can be used on any building type, and also can provide some fire resistance. EIFS is not noncombustible and special fire tests are required by code to confirm the performance. Some EIFS products are for residential (combustible) construction only for this reason. For EIFS-clad walls, the hourly fire resistance rating for the whole wall comes completely from the supporting wall; the EIFS does not add to the rating.
ThicknessStucco 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.
Stiffness and DeflectionStucco 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 deflection 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.
WindStucco is held to the wall structure with rigid fasteners and tough, strong materials like lath and cement. EIFS is often attached using plastic washers or with discontinuous bands of adhesive to sheathing. Although EIFS walls can be designed to handle huge wind loads, the lightweight nature of the EIFS attachment system needs to be examined to be sure it can handle the loads. For low-rise buildings, like homes, this is rarely a problem, but in hurricane areas it can be. On the tops of tall buildings, especially at the corners where the loads are the highest, this load capacity issue and factors-of-safety need to be addressed. This is normally done by reviewing data provided by the EIFS producer that shows wind load capacities for various studs, spans, fasteners and sheathings. With EIFS, an adhesively bonded system on a strong substrate gives the strongest wall. The whole wall, including the stud connection to the building frame, as well as the sheathing and the sheathing fasteners, needs to be explored.
DrainageMost codes now require that EIFS used on wood-frame buildings incorporate drainage into the EIFS. If switching from stucco to EIFS, on a wood frame building, a traditional barrier type EIFS may not be code-compliant, and EIFS with Drainage costs more and is slightly thicker. Also, the detailing is different, including water barriers, flashings, and so on. EIFS with drainage is usually about 20 percent more expensive than traditional barrier EIFS.
Generic vs. SystemStucco is a generic product and is listed in the codes as its own building product. Countless books and specifications exist for various types of stucco. EIFS, on the other hand, are proprietary systems and are just starting to be fully described in the codes as a product type. When specifying EIFS, you do so based on specific EIFS brands and “approved equals.” With stucco you simply specify which of the many standard types of stuccos you want. In between EIFS and stucco are the many hybrid EIFS/stucco systems, most of which are proprietary and are also specified, like EIFS, as systems.
JointsOne of the big selling points with EIFS is that it can often be installed with very few joints. This requires a stable substrate that is also jointless. Stucco, due to its chemical nature and shrinkage during curing, needs control joints about every 144 square feet. If switching from EIFS to stucco, the elevations–and the location of control joints on them–need to be worked out. The location of the joints, where none existed before, can have a big effect on the appearance of the wall. With stucco and EIFS, if there are through-wall expansion joints in the substrate, then both stucco and EIFS need expansion joints there too; they can never bridge a working joint.
InsulationEIFS is an insulating system; stucco is not. Perhaps the biggest change when going from EIFS to stucco is the reduction in R-value of the whole wall. It’s easy to lose more than one half the R-value. This can necessitate adding a large amount of insulation in the stud cavity or other techniques to bring the total R-value up to energy code compliance. The reverse is also true: going from stucco to EIFS can increase the R-value substantially, perhaps letting you go from 2 x 6 studs to 2 x 4 studs.
HardnessEIFS is softer than stucco and does not take a beating as well as stucco. Sometimes EIFS buildings use stucco (with EIFS finish as the final coat) at the on-grade areas for this reason, and a full EIFS system on the upper floors. If using EIFS, consider what areas may be impacted by people and objects, and if using EIFS in those areas, beef them up with heavy reinforcing mesh, or protect the EIFS so that run-away shopping carts and lawn mowers can’t gouge them.
Vapor BarriersEIFS walls have the insulation outboard of the wall structure. Stucco has the insulation within the wall. The heat and water vapor flow through the wall changes depending on which system is used. In areas with extreme climates (arctic versus hot/humid, and extreme indoor activities, swimming pools, etc), the need for, and location of, vapor barriers, need to be considered. EIFS producers have computer programs that can analyze the wall and let you know what, if anything, is needed.
The FinaleAll of the above considerations are not the only ones. But the key is to think about what implications there are for changing claddings––how would your bid be affected? As they say, “The Devil is in the details”.
Changing EIFS to stucco, and vice versa, is quite common, and doing so successfully is usually quite feasible. It’s simply a matter of thinking through the various issues involved (described above) and making allowances for the change. Often the difference in cost between EIFS and stucco is so close that the design is made more on the basis of energy savings and aesthetics, than on simply saving money. The oddest switch I’ve run into was a real deal-breaker: the owner wanted to switch from stucco to EIFS. The building was right on the lot line. When the foam was being installed, the neighbor raised hell about having the building on his land, and called out some surveyors. Rather than move the whole building, they switched back to stucco.