by Russell J. Kenney & Michael E. Kenney The exterior insulated finish system, or EIFS, has been on the market in America since the early 1970s. EIFS came here from Europe, where it had been used successfully since the late 1940s, gaining popularity as an effective and affordable way to renovate older buildings and restore buildings that were damaged in the Second World War. Unfortunately, the version of EIFS that was brought to this country was very different from the system that had worked so well in Europe. Modifications were made to the system with very little testing and engineering analysis. Problems started to crop up soon after EIFS entered the U.S. market, and as most people know, North America had widespread EIFS failures in the 1980s and 90s. Our company has prospered investigating many of those problem installations, serving as consultants in court cases involving everything from houses to high-rises. We've learned a lot about why and how EIFS can fail, but we haven't given up on it as a system. EIFS has advantages: It's fast, it's economical, and it offers a lot of control over style and appearance. And done right, it works. If you understand the design issues, the materials, and the installation process, you can get good results with EIFS. We don't just investigate failures — our company has supervised millions of square feet of EIFS work on new and existing buildings, and we have confidence that those installations will perform acceptably. As a result of our investigations of EIFS problems on buildings nationwide, we've proposed a number of changes in American codes and standards that apply to EIFS. Some of our recommendations have been adopted by the codes or by manufacturers, and some haven't. Since everyone hasn't seen fit to change their specifications, we've developed our own standards for jobs we supervise. Our company reviews plans, writes specifications, and inspects or supervises EIFS work on site. We provide advice on system design, materials selection, and installation methods. How the system is installed is usually the critical factor, but the design and the materials can also affect performance.

Barrier EIFS Versus Drainage EIFS

To put EIFS cladding on a building, the EIFS contractor first attaches expanded polystyrene (EPS) insulation board to the wall structure. This rigid foam base then gets covered with a base coat formulated from water, acrylic polymer, Portland cement, aggregates, and fillers. Fiberglass reinforcing mesh is embedded in the wet base coat. After the reinforced base coat sets up, all joints are sealed with caulk or sealant; a finish coat is applied to the whole system for color and texture. The result is a (mostly) waterproof skin with an attractive appearance. In the original EIFS system, the insulation board was attached directly to the building with adhesive, and the base and finish coatings (along with the sealants) were the building's main defense against rain. That system is called "barrier EIFS," and it has worked well on concrete and masonry buildings in both Europe and America. Over time, there are sure to be cracks in the lamina (composed of base coat, mesh, and finish coat), as well as partial sealant failures at joints; but concrete and masonry buildings don't tend to suffer damage from the relatively small amounts of water that pass the exterior weather barrier. Buildings made with water-sensitive materials are a different story. If a building has wood framing and OSB sheathing (or light-gauge steel framing and gypsum board sheathing), the amounts of water that enter the wall through window assemblies, at interfaces between EIFS and abutting wall components, or through cracks in the EIFS lamina are sufficient to do serious damage to the structure below. The EIFS may look great on the exterior, but underneath, the building could be disintegrating. As the substrate deteriorates and the bond between the building and the EPS weakens, the foam and lamina experience more movement, the cracking gets worse, more water enters, and the problem grows. Sometimes large areas of EIFS can lose their bond to the building and hang loose, held in place by nothing but the caulking around the windows. In the end, the wind may tear off whole sections of the exterior cladding. For wood buildings, hidden structural rot can be fatal. We've investigated commercial buildings where underneath the EIFS, some of the backup walls were constructed of concrete or masonry, and other sections were made of steel framing with gypsum board sheathing. Often in those structures, the masonry sections are in good shape, with the EPS still well attached, while the parts of the building with a moisture-sensitive backup wall are basically falling apart. The difference comes down to how well the substrate can tolerate moisture. That doesn't mean that EIFS is restricted to masonry buildings. It can be effectively installed on a wood-sheathed or gypsum-sheathed structure. But wherever the sheathing consists of moisture-sensitive substrates like OSB or gypsum board, we recommend a "drainage EIFS" (also called "water-managed EIFS") design. This is also what the newer versions of the model codes require for residential construction (although not all jurisdictions have adopted that change). Since almost all houses are wood-framed with moisture-sensitive OSB or plywood sheathing, residential EIFS in general should be a drainage system.

Drainage EIFS Details

In a drainage EIFS system for wood-frame buildings, the wall is first covered with a protective water-shedding drainage plane material; then mechanical fasteners are used to attach the EPS board to the wall system (see Figure 1). This works well in buildings sheathed with plywood or OSB. (For commercial buildings that use gypsum sheathing, there are also drainage EIFS systems that rely on a liquid or troweled-on waterproofing layer and use adhesively attached EPS, but these are seldom if ever used for residential work.)

Figure 1. A drainage EIFS system relies on a drainage medium such as asphalt felt paper or housewrap to protect moisture-sensitive parts of the building against water that gets past the surface coatings. Foam board is attached over the drainage plane using mechanical fasteners; then base coat is troweled onto the foam, and fiberglass mesh is embedded in the base coat. Finally, a finish coat is applied over the reinforced base coat. Effective flashing details and joint sealing are critical to the success of the system.

Major EIFS manufacturers that supply drainage EIFS systems all have some sort of requirement for creating an air space or capillary break between the EPS board and the drainage material covering the wall. One method is to use a "crinkle wrap" variety of housewrap such as Tyvek's StuccoWrap. Another method is to use a type of EPS board that has a grooved, wavy, or waffled back profile, so that the board contacts the wall only in spots, creating drainage channels between the board and the weather-barrier drainage material. Both systems work acceptably. In fact, we've tested EIFS systems using ordinary flat-backed EPS board over regular housewrap or asphalt felt and found that drainage occurs readily even without the "drainage channels." If you apply the EPS board flat to the paper, apply base and finish coats in the regular way, then cut a hole in the EIFS eight or ten feet up the wall and actually pour water in, you'll soon see the water drain out through the weep holes in the drainage track at the bottom of the wall. Water drains behind the EPS, as well as through it. It's true that our own specs, like the major manufacturers' specs, do call for drainage-channel EPS board or crinkled housewrap, but that is mainly because we want the warranty to hold. The "secondary weather barrier" beneath the EIFS should include not just a water-shedding drainage material (typically asphalt felt or housewrap), but also a system of flashings for all penetrations in the envelope, including windows, doors, outside lights, dryer vents, hose bibbs, and exterior electric outlets. Transitions where exterior decks are attached or where roofs abut walls also need foolproof flashings. All the flashings have to be integrated with the water-shedding drainage plane so that water flowing downward will always go on top of the drainage material, not behind it. Before the EIFS goes on, you should be able to spray the whole building with a hose and have no water contact the framing or sheathing. To work right, the whole drainage plane system has to be carefully considered and properly installed. We've created some standard flashing details that are adaptable to most situations, but it's not possible to design a standard detail that will cover every possible scenario. In unusual cases, the trick is to "think like a raindrop." Water on a surface will generally seek to go down, although it may travel sideways or even up when it contacts very small cracks and capillary openings. When you come to a building element that calls for a custom flashing detail, just make sure that gravity will pull the water down and away from the wall, without bringing it into contact with fine cracks or narrow openings.

EIFS Materials and Installation

When the secondary weather barrier is done right, the building will be resistant to water damage even if the EIFS, windows, or caulking has some leaks. Nevertheless, the EIFS also should be installed correctly. The more waterproof and durable the EIFS skin, the better. Installation details matter, and so does the choice of materials. The goals are to prevent leaks, to resist weathering, and to minimize cracking and sealant failures over time. Our company has investigated every material used with the EIFS system — the EPS board, the base coats, the fiberglass mesh, the sealants, and the finish coats. We've noticed that the European standards for most of those materials are stricter than the American standards, and in most cases, we believe that the stricter European standards are better. Unfortunately, because of the relatively weak U.S. industry standards, it's not always possible to get the same materials in America that are available in Europe. EIFS made with American materials may be less durable than EIFS in Europe, even if the installation details are the same (all the more reason to be careful about the secondary weather barrier). However, given what's available on the U.S. market, it's still worth the effort of choosing materials carefully and applying them correctly. In our jobs, we use materials supplied by the major manufacturers that have been in the EIFS business for many years: Dryvit, Parex, Senergy, and Sto. However, all those companies offer installers a menu of choices in drainage wrap, EPS board, reinforcing mesh, and coatings. Our specs call for certain choices from that menu. . EIFS requires a soft insulation board that can move without cracking (Figure 2). Because it must be soft, the board is not dense, and the nominal one-pound EPS board that is typically used for EIFS is not watertight. In Europe, EPS board is generally made using a vacuum process that results in a denser, less porous board. American EPS is most often made with a steam process and is generally less dense and more porous. The American manufacturing standards for a nominal one-pound-density board require an actual density of only .9 pounds per cubic foot; but in tests we have performed, most boards on the market achieve that density barely, if at all. The standards also allow the board to absorb 2.5 times its own weight in water; in effect, the foam is allowed to be a sponge.

Figure 2.A worker attaches soft EPS "beadboard" with screws to form the base of the EIFS cladding. The close-up, below, shows the voids between the plastic beads. EPS allows water to leak through and can hold moisture against the building. That is why careful joint sealing and an effective secondary weather barrier are critical to system performance.

Water can take minutes or hours to pass through EPS board, depending on the density of the board. But in any case, the EPS generally does not protect the house against water. Water that gets to the foam will trickle through it or through joints between foam pieces, and if the water can't drain out, it will collect at low spots. Trapped moisture in the foam can create moist conditions next to the wall. So it's critical to prevent cracking in the EIFS surface, to seal all joints effectively, to detail the secondary weather barrier carefully, and to allow drainage throughout the system.

For mechanically attached EPS, our spec calls for foam boards greater than one inch thick.