EIFS Update: Pick the Right Substrate  

Exterior Insulation and Finish Systems (EIFS) are currently a popular choice as an exterior cladding system throughout the country for commercial construction and to a lesser extent, residential as well. While there are multiple manufacturers of EIFS, they all share the same basic make-up in that they are multi-layered exterior wall systems combining continuous rigid insulation with a reinforced, field-applied finish. In that regard, they have been shown to provide superior energy efficiency, better moisture control, and offer much greater design flexibility than other cladding products. To be successful, however, the system must be designed and installed correctly, and just as importantly, it must be installed over an appropriate substrate on an appropriate wall system. Lessons learned in the past decade or so from manufacturers, installers, and architects reinforce the need to understand how all of the parts and pieces of a total EIFS wall system work together for energy and moisture control, aesthetics, economy, and sustainability.

Exterior Insulation and Finish Systems Characteristics

Figure 1: The typical components in a total wall construction using an Exterior Insulation and Finish System (EIFS) Image courtesy of STO Corp.

According to the EIFS Industry Members Association (EIMA), EIFS were initially developed in Europe in the 1950s then introduced in the U.S. almost40 years ago. "They were first used on commercial buildings, and later, on homes. Today, EIFS account for nearly 30 percent of the U.S. commercial exterior wall market." EIMA and others point out that a total wall system using EIFS typically consists of the following components (See Figure 1).

• Wall framing on steel studs is designed and installed in standard fashion either as the structural component of the wall or as infill between the primary structural frame. Depending on a given situation, insulation may or may not be installed between the wall studs. Further, since the EIFS is lighter in weight than masonry, stone, or concrete cladding, the impact on the structure is less, often resulting in some cost savings on the structural frame.
  
  
• A solid substrate panel attached to the outside of the studs. This is the layer that is typically installed by someone other than the EIFS subcontractor, but has a big impact on the performance of the system and the flow of construction activity. Not surprisingly, manufacturers and technical specialists have developed particular and stringent requirements for this substrate layer. Further, the joints of this layer need to be covered with an appropriate mesh or wide tape-like seal.
  
  
• A water-resistant barrier or liquid membrane applied over the substrate before the installation of insulation. This barrier has been added in recent years in response to some past concerns about water penetration into the rest of the wall assembly and has been shown to be an effective solution to those concerns.
  
  
• Insulation board adhesive typically consisting of a specially formulated make-up to adhere to the membrane-coated substrate as well as the insulation. The prevailing installation method is to install the adhesive in continuous vertical ribbons that allow any trapped moisture to drain down the surface of the coated substrate and weep out the bottom. While less common, the insulation can also be held in place with mechanical fasteners, although each fastener will obviously compromise the integrity of the water-resistant barrier.
  
  
• Rigid insulation boards that are commonly made of expanded polystyrene (EPS) or polyisocyanurate foam and can range in thickness from 1 to 4 inches. The preference is for a single board of the desired thickness rather than multiple, overlapping layers requiring additional labor and potential for separation. The insulation is usually set into a base channel or starter track mounted at the bottom of the exterior wall. This track is intended to contain regularly spaced weep holes to allow the release of any trapped moisture but not compromise the thermal integrity of the wall.
  
  
• A formulated base coat that is durable and water-resistant is then hand applied on top of the insulation. Fiberglass mesh is commonly installed as part of this base coat as reinforcement for added tensile strength.
  
  
• A finish coat selected for attractiveness and durability. Typically this finish coat is made with an acrylic material that employs co-polymer technology, all of which is known to be both colorfast and crack-resistant. In some cases, an intermediate coat may also be applied between the base and finish coats.

Figure 2: Comparison of composite or whole wall R-values in different types of walls using fiberglass insulation between wall studs versus 4" exterior insulation. Image and data courtesy of STO Corp. and the Oak Ridge National Laboratory

Variations do occur in this make-up between different manufacturers and for different applications, but the fundamental process is the same and produces the same basic characteristics of the wall. According to the National Institute of Building Sciences (NIBS)Whole Building Design Guide, those characteristics include the following four quoted in part below:

• First, placing all of the insulation outside of the wall cavity reliably locates the dew point (the temperature at which humidity condenses to form water) outside of the wall cavity. This is a key consideration. Dew formation inside the wall can create conditions conducive to mold growth and material decomposition. Cavity insulation moves the dew point inward, and should be balanced with an appropriate amount of exterior insulation. By exploiting the high insulation value of insulation board used in an EIFS, walls can be designed to locate the dew point outside the wall sheathing. In an EIFS with drainage, sheathing is protected with a secondary water-resistive barrier and a drainage plane. Design professionals should always evaluate dew point locations for their projects.
  
  
• Second, exterior insulation eliminates thermal bridging (heat transfer across a solid element such as wall framing). This is a very important consideration that has gained increased attention in recent years. In many climate zones, steel framed walls cannot meet prescriptive requirements without continuous exterior insulation. This is because thermal bridging reduces the effectiveness of cavity insulation by up to 65 percent. (See Figure 2.)
  
  By way of example, R-21 batt insulation in certain cases delivers as little as R-7.4 actual measured performance. The reason for this decrease in performance is the regular interruption of the insulation by the wall framing at 16 or 24 inches on center plus top and bottom tracks/plates and framing around openings. The combined area of all of that framing can account for up to a third of a wall surface with a substantially lower or even negligible R-value. Worse yet, steel studs efficiently conduct heat across their depth accelerating the unwanted heat flow. Using exterior insulation eliminates this problem since all of the framing is contained inside the thermal envelope of the building and does not have an opportunity to create a thermal bridge to the exterior. Hence, the building is capable of performing to its full energy efficiency potential.
  
  
• Third, rigid insulation board can be highly cost-effective. Increasing the thickness of the insulation board adds insulation value for material cost only, since little or no extra labor is needed. In addition, all costs associated with cavity insulation can often be eliminated.
  
  
• Fourth, thermal expansion and contraction of the building framing is dramatically reduced because framing is no longer subject to daily temperature changes. This reduces building movement and associated stresses.

NIBS goes on to point out that the only drawback they find to a completely exterior insulation system is a slight increase in overall wall thickness which presumably can be addressed by appropriate design measures.

Importance of the Substrate

Particularly important for the installation of EIFS, as it is for other wall types, is the choice of sheathing that forms the substrate upon which to build the EIFS. Common choices in the past have included plywood and paper faced exterior gypsum board. It didn't take long to realize that these choices had some distinct limitations and the potential for some severe problems.

First, the organic nature of wood and paper surfaces means that they are not particularly well suited to withstand weather exposure during construction. If they became wet, they would swell and cause deformities which telegraphed through the EIFS causing unwanted irregularities in the final surface. For the contractor to reduce the amount of weather exposure on the sheathing, the installation of the sheathing would need to be protected and then coordinated with the installation of the EIFS. This could mean delays in the construction process since the building might not otherwise be considered fully enclosed enough for other aspects of the work to occur. It would also mean the contractors would need to return afterwards to try to correct the defects caused by the weather exposure on the sheathing, often with limited real success.

Second, the presence of wood and paper provide one of the key ingredients for mold formation in walls: organic food. It is commonly understood that mold requires this organic material to feed on in addition to the presence of water and favorable temperature conditions. In the course of building design and construction it is problematic to completely eliminate moisture or even water in an assembly. Similarly, the range of temperatures that a wall assembly experiences in order to be favorable for human habitation is also favorable for mold growth. Hence, the only real tool to combat mold growth is the elimination of the organic material.

Third, the nature of both plywood and paper faced gypsum is that the outermost surface is laminated to interior surfaces within the substrate. Under normal conditions, the lamination process is appropriate and suitable to many applications. However, if moisture entered the space between the EIFS and the substrate, that lamination process was compromised and the outermost layer would sometimes separate (delaminate), causing the EIFS to literally come apart from the building it was applied to. This was clearly a problem and one that wasn't likely to be solved by trying to seal out all moisture in the wall.

Figure 3: Paper free, fiberglass mat embedded gypsum sheathing panels being used as a substrate on the Medical University of South Carolina Ashley River Tower, Charleston, South Carolina Architect: NBBJ and LS3P Photo courtesy of Georgia-Pacific Gypsum

Given these limitations and the significant problems with these organic substrates, a suitable alternative was sought and often required by regulators and EIFS manufacturers. Over the past decade, a number of sheathing manufacturers have looked for and developed alternatives. Currently, the most common choice is to specify engineered exterior gypsum sheathing. (See Figure 3.)

This type of sheathing typically contains a specially treated gypsum core with embedded fiberglass mats on both sides of that core. This process is referred to as glass mat bonding and means that there is no lamination that can become separated - the core and the surface are integral. And since mineral based fiberglass is used, the presence of organic materials is eliminated. The result is that this type of glass mat bonded sheathing provides superior moisture, fire and mold resistance. From a construction standpoint, it means that this type of sheathing and EIFS substrate can remain exposed to normal weather conditions for up to twelve months and still perform admirably.

An additional requirement imposed on the sheathing is the ability to act as a true drainage plane. In previous decades, EIFS installations were experiencing water problems, particularly in southern climates on residential applications, where water vapor resulting from high humidity conditions was entering and getting trapped between the insulation and the sheathing substrate. This caused the predictable problems of physical damage and deterioration along with the associated liability and business concerns. Once again regulators and manufacturers sought and found solutions. The current dominant approach is to use a vapor permeable air and moisture barrier, usually liquid applied. This barrier assembly protects sheathing from moisture intrusion and air leakage and allows the finished surface to act successfully as a true drainage plane. Hence, any moisture that does enter the wall assembly, either from inside or outside of the building, can drain down the surface of the sheathing. Of course, this means that there needs to be appropriate space for that drainage. In the case of EIFS, the simple act of installing the adhesive in vertical strips that are compressed to about 1/16- to 1/8-inch is adequate. Moisture can then drain down between these vertical strips to a starter strip or track at the base of the insulation, and weep out the bottom. Hence, even if moisture does find its way into the wall, it can now drain safely away without causing any damage. All of these advances and protections have come about because of the attention paid to using the appropriate substrate, coating it appropriately, and recognizing the importance of the surface where the EIFS meets the rest of the building.

Comparing Wall Systems

Part of the evolution of EIFS to their current improved state has been extensive testing and research on types of wall systems and comparisons with other, traditional wall systems. Among other studies, one notable one has shed considerable light on the science and performance of these systems. The U.S. Department of Energy (DOE), through the Office of Energy Efficiency and Renewable Energy's (EERE) Building Technologies Program, and in conjunction with the EIFS Industry Members Association (EIMA), sponsored an Exterior Wall Cladding Study which was conducted by researchers at the Oak Ridge National Laboratory (ORNL). A building was constructed near Charleston South Carolina, containing multiple wall panels with various wall claddings and assemblies.

Each of these wall panels contained sensors that provided a full profile of temperature, heat flux, relative humidity, and moisture content. These sensors collected data 24 hours a day, 7 days a week, and transmitted the data to the ORNL research facility in Oak Ridge, Tennessee for analysis. One of the strengths of this study is that it considered the building envelope in its entirety, along with studying isolated materials or components of the exterior claddings. The other strength is that the wall was exposed to real climactic loads. As a result, this study allowed the researchers to gather real-world data over a 30-month period between January 2005 and June 2007. The Phase 1 and Phase 2 results of this study were released on August 15, 2008.

The focus of this 30-month evaluation was on the overall moisture and thermal (hygrothermal) performance of EIFS, stucco, and masonry walls. The following excerpt from the Executive Summary of the report outlines the key findings of this study, all of which are applicable to a mixed, coastal, Zone 3 climate similar to Charleston, SC:

• One of the best performing wall system configurations was comprised of EIFS that included a liquid applied water-resistive barrier coating and four (4) inches of expanded polystyrene insulation board. In addition, all of the thermal insulation was placed outbound of the sheathing (no stud cavity insulation). This EIFS wall configuration performed better than brick. Brick had the lowest thermal and moisture performance among the claddings and wall configurations studied, followed by stucco (both 3-coat and 1-coat).

• EIFS walls maintained a consistent, acceptable level of moisture (average monthly relative humidity below 80 percent, as defined by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) SPC 160P, now referred to as ANSI/ASHRAE Standard 160 Criteria for Moisture- Control Design Analysis in Buildings within the cladding despite varying outdoor conditions when appropriate interior vapor retarders were used. Brick and stucco tended to accumulate slightly more moisture during both Phase I and Phase II of the project and retained moisture longer than EIFS.

• EIFS and a liquid applied water-resistive barrier coating readily dispersed moisture introduced by flaws (installed in Phase II) in the building envelope, as compared with brick, which retained more water.

• Liquid applied water-resistive barrier coatings, in certain instances, outperformed other water-resistive barriers in this study. In addition, EIFS with water-resistive barrier coatings performed significantly better than other EIFS claddings that used building paper or spun-bonded polyolefin membranes. The results also indicated that building wraps permit greater vapor transport inward in mixed climates.

• Insulation located on the exterior (outside of the stud cavity) is more effective since it maintains the sheathing and insulation at drier levels. This has important implications for preventing material degradation.

• The results of this study validate that vertical ribbons of adhesive provide an effective means of drainage within an EIFS clad wall assembly.

Figure 4: ORNL determined that the best performing system used non-insulated cavity walls, a drainage plane membrane, vertically applied adhesive, and a 4" EIFS cladding. Image courtesy of ORNL and EIMA

Each of these findings demonstrates and validates the prevailing practices related to the design and installation of EIFS in buildings. As such, they essentially declare that prior problems experienced with this cladding technique have not only been overcome, but that they surpass other traditional systems such as masonry and stucco walls in terms of hygrothermal performance. Further, the wall system found to have the best overall performance, namely an EIFS with 4" of EPS insulation and an air barrier (See Figure 4)meets or exceeds all ASHRAE and Core Performance Guide insulation and air barrier requirements in the continental U.S. and much of Alaska. The stated results of this study are summarized as showing that:

"EIFS are capable of controlling temperature and moisture within the wall system and outperform other exterior claddings during the monitored year. In essence, EIFS have the ability to maintain an acceptable balance of moisture and temperature control that is indicative of a well-designed, properly operating energy efficient building without moisture problems. All of the wall configurations evaluated in this study performed satisfactorily. This study convincingly proves that EIFS is an excellent choice for achieving key building performance goals, including energy efficiency, moisture and temperature control. EIFS absorbs less moisture and heat as does brick and stucco. These results clearly and convincingly demonstrate the superior performance of EIFS in a mixed, coastal, Zone 3 climate."

A complete report on both Phase I and Phase II is available at theOak Ridge National Laboratory web site.

Meeting Code Requirements

The International Energy Conservation Code (IECC) developed by the International Code Council (ICC) has been the baseline for minimum energy performance in buildings in at least 40 states around the country for some time. The 2012 IECC improves energy efficiency by 30% compared to the 2006 IECC and is endorsed by numerous professional and trade organizations. Based on the demonstrated superior performance of EIFS in the ORNL study, this system is poised to easily meet or exceed the updated requirements while other systems will need much more design attention in order to comply.

In a related effort, the ICC also launched in 2012 the International Green Construction Code (IGCC) focused on developing a model code applicable to both new and existing commercial buildings addressing more fully green building design and performance. The IGCC is meant to be a complementary code, not a replacement to the rest of the family of codes developed by the ICC including the Building Code, the Residential Code, and the Energy Conservation Code. The IGCC was developed with input from the American Institute of Architects (AIA), the American Society for Testing Materials (ASTM) International, ASHRAE, the U.S. Green Building Council (USGBC) and the Illuminating Engineering Society (IES). As such, it is seen as an emerging, collaborative, standard for green building and energy efficiency standards in the U.S.

The unique feature of the IGCC is that it contains multiple levels of compliance. First, it includes baseline requirements of performance in buildings for energy and water use among other things. This means that jurisdictions that adopt the IGCC may require greater levels of energy performance in both new and existing buildings. There are also further options where the local jurisdiction will be able to add some additional, more stringent requirements to buildings in their communities, specifically related to energy and water use. And finally, there are electives to the code which are similar to the green building standards promoted by the USGBC and others. These electives allow for recognition and encouragement of further reductions of energy usage even beyond the higher requirements of the base IGCC or those imposed by the local jurisdiction. As has been demonstrated already, EIFS can be very effective in helping to achieve not only the increased minimum energy requirements, but also exceed those levels to achieve better performance and points under the elective section of the IGCC. As such, a properly designed and constructed EIFS building can achieve the client's requirements, satisfy the science and weathering needs of the building and perform beyond the requirements of existing and emerging codes.

The recognition of this positive code compliance capability has been embraced by the industry. "We see very little downside and a lot to gain from it," says Dave Johnston, executive director for the ElFS Industry Members Association. "If there is a wall cladding that can meet the energy efficiency requirements in the International Codes it is going to be EIFS." That type of commitment is good for the construction industry looking to produce quality construction, good for building owners looking for the best value, and good for architects looking to produce holistic, sustainable design.

Case Studies

EIFS with appropriate sheathing systems are used extensively for new construction and increasingly for retrofitting and renovations of existing buildings. And they are equally appropriate for commercial/institutional construction as for residential construction. To demonstrate the application of these systems further, the following case studies are offered.

Field Test on New Condominiums in Maine

Figure 5: Six months of exposure to the winter weather in Maine resulted in virtually no effect to the fiberglass mat exterior sheathing used on these condominiums in 1984 to 1985. Photo courtesy of Georgia-Pacific Gypsum

A quarter century ago, during a typically frigid winter on the seacoast of Maine, two partially completed structures weathered the storms and icy temperatures quite well. And, much like the lighthouses that dot this craggy shoreline at the family resort of Old Orchard Beach, south of Portland, the buildings shone a light on something significant - in this case, the beginnings of a new way to construct commercial and residential properties. Pat Huempfner proudly remembers that time, in late 1984. Then a just-hired sales representative for an engineered exterior gypsum product, he recalls that the two condominium projects-five- and seven-stories tall, respectively-were the first installations of a product that would revolutionize the construction industry: fiberglass mat exterior sheathing. "Every gypsum company was looking for a way to avoid all of the issues related to paper-mold, moisture, warping and delamination," says Huempfner. But it was a concerted research and development effort that made the big breakthrough. Indeed, at testing laboratories on the opposite coast of the U.S., near Portland, OR, researchers had made a significant discovery. They invented a patented technology breakthrough whereby a gypsum core could be effectively wrapped in a fiberglass mat and embedded in the core, eliminating the need for gypsum panels with paper facing. Traditionally, gypsum panels were produced by encasing a slurry of calcined gypsum plaster with paper facings-so this new fiberglass-based method was a momentous innovation. "By every indication, it looked like it would work great," recalls Huempfner. "But we needed to field test it to be sure." They teamed up with EIFS manufacturers who were quite understandably eager to find an improvement on traditional paper-faced gypsum sheathing. This was particularly vital in cold-weather environments, since the final coating on an EIFS system requires that the ambient temperature be above 40 degreesFahrenheit. "It was October, and the two under-construction projects on Old Orchard Beach would be exposed to cold weather for about six months, because it was too cold to finish the EIFS job," explains Huempfner. Two other condominium projects that were under construction stood nearby, which were also on hold for the winter. Those, however, had been built using paper-faced exterior sheathing. So, while field testing of the exposed fiberglass mat sheathing was going on, the opportunity emerged to compare its performance side-by-side with the technology it hoped to replace. "We were going to get six months of snow, rain, ocean salt and wind-we couldn't have asked for a better test," emphasizes Huempfner. And as it turned out no one could have asked for more dramatic results. Despite bracing winds and sub-zero temperatures, the embedded fiberglass mat gypsum exterior sheathing performed impeccably on the two condominiums where it sat exposed. "Six months later, when winter was over and it was warm enough to finish the EIFS, these panels held up beautifully," says Huempfner. "Not one of them had to be replaced." And the other two under-construction condominiums, which had left paper-faced gypsum panels exposed to the harsh Maine winter? Over 50 percent of those panels had to be replaced, recalls Huempfner-and, of course, this time they used the new fiberglass mat sheathing. Tom Remmele, now technical director for an EIFS manufacturer is also grateful for the groundbreaking work done to introduce fiberglass mat gypsum sheathing into the market as a substrate for EIFS."This was the first of its kind and really overcame the exposure limitations of ordinary paper-faced gypsum sheathing," says Remmele."The early work done to marry the sheathing with the EIFS products has now formed the basis for many years of successful installations.We continue to specify fiberglass mat gypsum today as a substrate for EIFS." Ten years later, while on business in the area, Huempfner and a colleague returned to Old Orchard Beach to see how the condominiums that had first used this fiberglass mat sheathing were holding up. He was not surprised to learn that nothing had changed in a decade. "We spoke to one of the owners, and looked closely at the structures," he recalls. "The buildings looked great." Interestingly, they discovered that one of the structures had incurred some leaking in a carport ceiling, and that 3/8" holes had been drilled to allow the water to drain out sometime after the leak had occurred. "We thought it was amazing that the water build-up-over time-did not negatively impact the sheathing panel in that area," adds Huempfner."We call it 'moisture forgiveness'," he said, "because this substrate may give you enough wiggle room during the life of the building to survive this type of event." "It was exciting to be at the forefront of something big," says Huempfner, "and to continue to see how well received these sheathings are-and how well they work-to this day." And while other companies have entered the fiberglass mat gypsum sheathing industry, Huempfner is quick to emphasize that it is the quarter-century legacy of innovation, field testing, experience and leadership-all of which crystallized during that frigid winter on the coast of Maine-that made the difference.

Peter J. Arsenault, FAIA, NCARB, LEED-AP is an architect and sustainability consultant based in New York State and writes on topics related to sustainable design and practice solutions nationwide. He can be reached at www.linkedin.com/in/pjaarch