- Aesthetic Opportunities
- Air Barrier Systems in Buildings
- Blast Safety of the Building Envelope
- EIFS, Architecture, and the Sustainable Design Revolution
- Flood Resistance of the Building Envelope
- Indoor Air Quality and Mold Prevention of the Building Envelope
- Life-Cycle Cost Analysis (LCCA)
- Mold and Moisture Dynamics
- Wind Safety of the Building Envelope
High Performance EIFS
Last updated: 03-14-2012
Exterior Insulation and Finish Systems (EIFS) are lightweight, insulating wall claddings that give designers a wide range of aesthetic and performance options. The smooth outer surface of an EIFS, combined with decorative finishes available in thousands of colors and textures, provide an extensive and versatile design palette. And because EIFS are cost-effective, they can bring style and beauty to everyday structures.
EIFS are used on a wide range of commercial, institutional, and residential buildings. They can be applied over steel stud walls, wood frame construction, or masonry. EIFS can also be used to reclad existing buildings to create a refreshed appearance with substantially upgraded insulation value.
For design professionals, it is important to know that EIFS are systems that can be configured in many ways. Decisions made in the design stage impact the appearance, properties, and long-term performance of EIFS claddings. This article outlines design selections that create High Performance EIFS with optimized properties.
EIFS—A Brief History
EIFS were invented in Germany in the late 1940s to insulate existing masonry buildings while retaining a classic appearance. The technology was brought to North America in the 1960s. Building code agencies issued Evaluation Reports in the 1970s, setting the stage for large-scale acceptance in the 1980s.
Since then, EIFS have become one of the most thoroughly tested wall systems ever produced. After a comprehensive review, members of the International Code Council (ICC) voted to include EIFS in the 2009 update of the International Building Code and International Residential Code. Prior to this, EIFS were qualified as alternates to the building code under ICC Evaluation Reports held by individual manufacturers. From a building code perspective, the ICC action placed EIFS on the same footing as traditional materials like wood, steel, and concrete.
The Atlantis resort in the Bahamas is an example of a striking exterior appearance created using EIFS.
As requirements for sustainable construction become increasingly stringent, the light weight and thermal efficiency of EIFS gain new significance. In response, the EIFS designs most frequently specified are evolving to take greater advantage of the full spectrum of benefits that can be realized from these proven wall cladding systems.
The U.S. Department of Energy's Oak Ridge National Laboratory demonstrated many of these advantages in a 30-month study of brick, stucco, and EIFS wall claddings (PDF 69 KB). One of the study conclusions was that the best performing wall cladding they tested was an EIFS with 4" of EPS insulation and a fluid-applied water-resistive barrier. The Oak Ridge study1 illustrates both the outstanding performance that EIFS can provide, and the importance of decisions made by the design professional.
Design Professionals' Most Basic Choice—Barrier Wall or Water-drainage Design
Whether to employ a water drainage or barrier wall configuration is a design decision. Many wall claddings, including metal composite, precast concrete, glass curtainwall, brick, and EIFS are available in both configurations. All have the advantages and drawbacks generic to these wall design concepts.
Barrier walls are lower-cost designs that rely on an exterior primary weather seal to keep out moisture. EIFS, like most claddings, are also available with water-drainage designs. The key aspect of cladding designs with drainage is that these walls employ a secondary water-resistive barrier and a means to drain water that may get past the primary barrier. For steel stud and wood framed wall construction, EIFS with drainage is the basis for High-Performance EIFS.
EIFS Cladding—One Layer at a Time
Every layer in an EIFS performs at least two functions, which is one reason EIFS offer tremendous value. This section describes each layer, with case histories of successful performance.
Air and Water-Resistive Barrier
The innermost layer of an EIFS with drainage creates its greatest value when it is designed to act as an air barrier in addition to a water-resistive barrier.
Air barriers have been shown by the National Institute of Standards and Technology's2 NISTIR 7238 (PDF 972 KB) study to reduce HVAC energy consumption up to 15% in cooling climates and up to 40% in heating climates. This more than justifies the modest cost of adding an air barrier to an EIFS design.
A more recent study by the U.S. Army Corps of Engineers (PDF 3.35 MB) found that reducing the permissible air leakage from 0.40 cfm/ft² to 0.15 cfm/ft² can further reduce HVAC energy consumption by 8%–44%, depending on climate zone. Testing performed for the Army Corps of Engineers (PDF 1.3 MB) has shown this lower air leakage target to be realistically attainable.
There is another major benefit to building envelopes that include an air barrier. Air that infiltrates into the wall cavity can bring humidity with it, creating potential for condensation and subsequent corrosion/degradation of wall elements. Water in the wall cavity also promotes mold growth, which has a negative impact on indoor air quality. Air barriers thus promote building longevity and the quality of the interior environment.
The water-resistive barrier used in many EIFS have been tested and approved by code bodies such as the ICC Evaluation Service and the Air Barrier Association of America for use as part of an air barrier system. To form an air barrier system, the EIFS air barrier materials and assemblies must be integrated into an overall air barrier system that encompasses the entire building envelope.
Combined air and water-resistive barriers are an example of a synergistic design practice. Air barriers by definition have no holes. While this is not required of water-resistive barriers, a water-resistive barrier with no holes will clearly function as intended. Fluid-applied air/water-resistive barriers create a seamless, monolithic coating that is fully adhered to the sheathing, providing excellent resistance to water penetration, air movement and the cyclic pressure loadings that occur when a building is in service. Combining air and water-resistive barrier functions into one membrane is an excellent way to improve building performance and economy.
Pre-treatment of joints and transitions before final application of air/water resistive barrier. Fluid-applied air/water-resistive barriers effectively protect buildings from moisture and air infiltration/exfiltration.
The fluid-applied air and water-resistive barrier materials used in EIFS are designed to be compatible with adhesives used to fasten EPS insulation to the sheathing. Adhesively fastened EPS eliminates the need for mechanical fasteners that puncture the air barrier.
Many fluid-applied air/water-resistive barriers designed for EIFS have ICC listings that qualify them for use behind other wall claddings. On mixed cladding buildings, these products can be used as the air/water-resistive barrier material for the entire structure. This eliminates the need to transition air barrier materials unnecessarily and promotes coordination of jobsite workflow. The result is higher quality and lower cost.
Since air/water-resistive barriers are key to the long-term performance and energy-efficiency of a building, design professionals and building codes are increasingly specifying inspection of air/water-resistive barriers and performance testing of the final air barrier system. The U.S. Army Corps of Engineers and the General Services Administration (GSA) have adapted a test protocol based on the ASTM E779 Standard Test Method for Determining Air Leakage by Fan Pressurization. By testing the full air barrier system, design professionals can verify air barrier performance at a time when any shortcomings can be corrected.
Fort Bliss TX—24 new barracks were constructed with High Performance EIFS incorporating a fluid-applied air/water-resistive barrier. All of the buildings had less than 0.15 cfm/ft² air leakage.
Fastening Expanded Polystyrene (EPS) Insulation
The EPS layer of EIFS can be fastened to sheathing using an adhesive, or with mechanical fasteners. Many people assume that mechanical fasteners are stronger than adhesives. While the fasteners themselves are strong, they concentrate applied stress into small areas of the EPS board. As a result, the failure mode of mechanically-fastened EIFS under extreme wind load is rupture of the EPS.
The adhesively-fastened EIFS cladding on the Hard Rock Casino in Hollywood, FL looks great, and is designed to withstand hurricane-force winds.
Adhesive fastening spreads the forces applied to EPS over a larger area, producing a stronger bond that is more resistant to high wind loads. The typical failure mode for adhesively applied EIFS is sheathing detachment from the building frame or failure of the framing itself. EIFS that are adhesively fastened remain firmly attached to their substrate.
Adhesive can also perform two functions in an EIF system. By using a special trowel, vertical adhesive strips can create a drainage pathway that is part of the secondary water management system. These ½" ribbons, spaced 2" apart, securely fasten EPS to sheathing while channeling moisture to a drainage flashing. The result is a cost-effective water-drainage wall system that can be designed to withstand extreme wind loads.
Expanded Polystyrene (EPS) Board
The most multifunctional element of an EIFS is its expanded polystyrene board.
EPS thickness is a design choice that can pay big dividends in energy savings
The surface of EPS board is easy to sand or rasp to make it smooth and flat. It can be easily cut to create architectural reveals, and shaped to form an endless variety of architectural details and reliefs that enliven building aesthetics. These properties are the foundation of the design flexibility and outstanding aesthetic appeal of EIFS.
EPS also helps prevent the cracking so commonly found on conventional stucco walls. By protecting underlying framing from thermal expansion and contraction, exterior EPS insulation reduces the amount of building movement. It also absorbs the thermal expansion/contraction difference between framing and the exterior surface. Working in combination with the tough, flexible outer skin described below, EPS insulation helps eliminate one of the root causes of stucco cracking.
EPS has yet another function—thermal insulation. EPS board provides R-3.85 per inch thickness. Since all EIFS use EPS, designers can increase the R-value of their building envelope by simply specifying thicker EPS. Little or no additional labor cost is involved—extra insulation can be specified for the material cost of EPS alone.
Exterior Insulation Is Highly Efficient
IR thermograph showing thermal bridging (above left). Fort Bliss TX—IR thermograph showing the excellent thermal performance of EIFS with an integral air barrier system (above right).
EIFS put insulation where it works best, outside the wall cavity. By placing all of the insulation outside the sheathing, the location of the dew point (the temperature at which humidity condenses to form water) is reliably moved outside of the wall cavity. That makes EIFS an excellent choice in all climate zones. Dew point location is a key design parameter—if condensation occurs inside the wall cavity, the likelihood of mold and moisture damage is dramatically increased.
There are additional benefits to exterior insulation. Wood and particularly steel studs conduct heat past cavity insulation, reducing its effective R-value by up to 65% in metal framed construction. For example, R-21 cavity insulation can yield as little as R-7.4 actual insulation value3. EPS insulation placed outside the stud wall eliminates thermal bridging, and yields its full insulation value.
Continuous exterior insulation is increasingly recognized as a construction industry best practice for these reasons. As codes and standards increase thermal requirements for building envelopes, in many cases it is becoming impossible to attain required wall U-factors without exterior insulation. This creates new challenges for many traditional claddings that have historically relied on cavity insulation. In addition to dew point location, fire test data should be explicitly considered.
Since continuous exterior insulation has always been a key property of EIFS, these system provide a proven and fully tested way to meet continuous insulation requirements. Fire test data is available for EIFS using up to 13" of EPS insulation. Designs that employ an EPS thickness that provides all of the required insulation value can simplify construction and move the dew point outside the wall cavity.
Basecoat and Reinforcing Mesh
Acrylic polymer, portland cement and fiberglass mesh combine to create a tough, resilient, noncombustible outer skin
Along with EPS insulation, basecoat and reinforcing mesh together eliminate root causes of cracking often found with conventional stucco. Stucco is cement-based. Cement is tremendously strong in compression, but has very low tensile strength and elongation. When stucco is exposed to unaccommodated for building movement, it typically cracks.
Basecoat and mesh form a tough, resilient fiberglass-reinforced composite material. In an EIFS outer skin, strength is derived from the high tensile strength of fiberglass reinforcing mesh. The basecoat is comprised of a weather-resistant acrylic polymer/Portland cement combination. While conventional stucco relies on Portland cement alone, the combination of cement and polymer creates a tough, permanent, noncombustible matrix for fiberglass reinforcement. This matrix provides water resistance and effectively transfers applied stress into the high-strength fiberglass reinforcing mesh.
In most circumstances, 4-oz reinforcing mesh provides an appropriate amount of strength. For example, the Atlantis Resort, which has an EIFS cladding primarily comprised of 4-oz mesh, withstood 155 mph winds with negligible damage.
Where more strength is needed, often in high-traffic areas around the building, design professionals can specify heavier fiberglass reinforcing mesh and/or multiple plies of mesh. Cost can be managed by adding strength only where it is needed.
By specifying extra strength, designers can increase the damage resistance and longevity of EIFS claddings. High-strength EIFS can also be used on hurricane-resistant structures. The Miami-Dade large missile impact test is used to demonstrate that a structure can withstand impact and subsequent cyclical pressure loading. This test involves firing a full-size 2X4 board (8 feet long, 9-lbs) from a cannon at 50 ft/second. The board travels 10 feet and hits the EIFS wall dead on, with the full impact concentrated in a 2" x 4" area. After impact, the wall structure is subjected to cyclical loading. Not only can EIFS designs meet the Miami-Dade requirements, EIFS that place heavy mesh on the outer surface combine hurricane resistance with a strong, damage-resistant outer skin.
High Impact Case History
This picture of the Greenville SC Detention Center was taken in April, 2008, at which time it was 17-years old. Prior to construction, a series of mockups had been created to help the design team decide which exterior cladding would be most suitable. The designers created their own performance test—they smashed the mockups with a sledgehammer! When the dust had settled, a High Performance EIFS using 1-ply of 20-oz reinforcing mesh and 1-ply of 4-oz mesh was selected for the exterior of the Detention Center.
Holding strong—after 17 years, the Greenville County Detention Center continues to serve as designed
This video shows how High Performance EIFS respond to multiple sledgehammer blows—make sure your audio is turned on so you can hear the force of impact.
For the inner courtyard of the Greenville Detention Center, where detainees exercise, the architect specified an extra ply of 20-oz reinforcing mesh for super strength. This video demonstrates the incredible strength of High Performance EIFS, as it withstands multiple screwdriver impacts.
During construction, the architect was given an opportunity to value engineer this project by substituting lighter, less expensive mesh for the 20-oz high impact reinforcing mesh. Knowing the true value of strength and impact resistance, the architect declined this short-term savings. Years later, the value of this wise decision is apparent.
Architects designing high-value structures may wish to consider specifying one or two plies of 20-oz reinforcing mesh for high traffic/high abuse areas.
Textured Finish Creates Incredible Possibilities
The outermost layer is where High-Performance EIFS help designers showcase their aesthetic flair. Multiple appearances can be created by one application crew—easily, quickly and economically.
High-Performance EIFS contribute toward multiple design objectives, helping designers create buildings that meet the increasingly complex needs of 21st century architecture.
EIFS create the look clients want, with building science and environmental performance design professionals need, at a cost that works for everyone.
All building types