Energy-efficient building with EIFS

by Molly Doyle | December 24, 2013 9:23 am

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by Michael DeLaura, LEED AP BD+C
Among the efforts to create more energy-efficient and sustainable buildings, there has been a shift toward lightweight cladding options for the exterior. One such product is exterior insulation and finish systems (EIFS).

EIFS provide a number of features and benefits including an air barrier, continuous insulation (ci), and an aesthetic finish. The assemblies trace their roots back to early 1950s Germany. Originally designed for commercial use, EIFS made their way into the residential market in Europe a decade later. Introduced into the United States in 1969, the product has evolved over the last 45 years. It gained popularity in the 1970s as a result of higher utility costs and the need to improve energy efficiency.

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The original product consisted of an adhesive applied with a notched trowel to form vertical ribbons that attach the expanded polystyrene (EPS) insulation board to the substrate. The EPS was then rasped or sanded before application of a base coat; which then had a fiberglass mesh embedded into it. The mesh is embedded into the basecoat over the entire surface of the EPS for reinforcement of the system The final layer consisted of a decorative acrylic finish coat. The finish was available in a sand, swirl, or freeform texture, and offered in various colors. EIFS became a popular cladding since features such as curves, quoins, arches, reveals, and accents were easy and economical to fabricate and install. It offered a new look and an energy-efficient way to wrap the outside of the building providing continuous insulation and lowering heating and cooling costs.

EPS insulation can be installed up to 304 mm (12 in.) thick to achieve significantly higher R-values than other claddings, provided proper fire tests have been done with 304-mm thick EPS. Placing the insulation outbound of the sheathing eliminates thermal bridging, which, in some cases, can reduce the effective R-value between the stud insulation by nearly 50 percent.

Recent code revisions to the 2012 International Building Code (IBC) require use of continuous insulation outbound of the sheathing, making EIFS suitable for a building’s exterior. These code changes, along with technology advancements and introduction of the Leadership in Energy and Environmental Design (LEED) program, have also contributed to the development of the assemblies.

A recent U.S. Department of Energy (DOE) and EIFS Industry Members Association (EIMA) study conducted by the Oak Ridge National Laboratory (ORNL) shows the system can perform better than stucco, concrete block, fiber cement siding, and brick in energy efficiency, moisture intrusion, and temperature control. EIFS with fluid-applied air barrier and continuous insulation increases flexibility, while a drainage plane controls moisture intrusion and temperature. This can make it a suitable choice for mixed, coastal, and hot and humid climates.¹[3]

EIFS can contribute to LEED Points in the following categories:

• Energy & Atmosphere (EA), Credit 1, Optimize Energy Performance;
• Materials & Resources (MR), Credit 1, Building Reuse;
• MR Credit 2, Construction Waste Management;
• MR Credit 4, Recycled Content;
• MR Credit 5, Regional Materials; and
• Indoor Environmental Quality (EQ), Credit 4.2, Low-emitting Materials.
  

EIFS evolve with air/moisture barriers
Over the last 15 years, one of the biggest changes in EIFS assemblies has been the introduction of a fluid-applied air/moisture barrier installed over the substrate. This offers the option to use one continuous barrier over the substrate regardless of the cladding. The fluid-applied air/moisture barrier is seamless, and provides protection against moisture intrusion, water leakage, mold, and mildew.

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EIFS allow design flexibility, as the structure can be waterproofed with various claddings. The cladding itself was once thought to be the building’s weatherproof layer. One advantage of a fluid-applied air barrier is the building can be protected from inclement weather once the windows and doors are installed. All EIFS adhesives are compatible with fluid-applied air barriers.

The installation of the cladding can take place up to six months after the building has been dried in. This refers to the substrate and connections having a continuous seal. The exterior cladding, whether brick or EIFS, become a decorative feature.

However, with advancements in building science, cladding is now more of a decorative feature, and the air barrier and water-resistive barrier (WRB) the substrate protection and weatherproofing. Air barriers also lower heating and cooling cost and increase occupant comfort. Then help maintain constant temperature by controlling air leaks through the wall assembly, which can contribute to heating and cooling loss.

The National Institute of Standards and Technology (NIST) study, “Investigation of the impact of Commercial Building Envelope Airtightness on HVAC Energy Use,” confirmed air barriers promote energy savings from 30 to 40 percent for heating climates and 10 to 15 percent for cooling climates. An air barrier can be vapor-permeable or impermeable, depending on the climate and location. Impermeable air barriers are typically used in colder climates, and permeable air barriers are often used in warmer climates. The changes to the newest version of LEED will offer additional points in the Energy and Atmosphere (EA) category for air barrier and building envelope testing.

EIFS panelization
As more efficient building procedures developed, contractors started building with EIFS panels. Since panels are typically manufactured in an enclosed shop or warehouse, benefits include:

• increased quality control;
• highly engineered panels and connections;
• no interruption during inclement weather;
• improved productivity;
• little or no scaffolding required; and
• reduced safety risk in comparison to stick-built construction.

The panels consist of metal studs, sheathing, air barrier, adhesive, EPS insulation, basecoat, mesh, and finish. One of the major advantages of panelization is construction schedule compression since the panels can be manufactured offsite and installed as soon as the project site is ready. Panelization can significantly reduce the construction schedule as compared to stick-built buildings.

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Since the units are manufactured offsite, wall panels can be built while the floors are being poured. Once the floors are completed, panels can be installed using a tower crane onsite, reducing the entire construction schedule by 30 to 40 percent.

Panels can be either structural or non-structural. Depending on the type of construction and building height, both types may be installed on new or existing structures. The structural panel assembly consists of the following components:

• metal stud frame;
• exterior sheathing;
• air barrier;
• adhesive;
• insulation;
• basecoat;
• mesh; and
• finish.

The panels are taken to the site on a flatbed trailer; they tend to be sized to allow for economical transportation from the fabricator. They are attached to the substrate by being welded or bolted to a clip or anchor placed in the concrete when it is poured. Panels are usually installed using a tower crane already onsite. A double silicone sealant joint is typically placed between the panels to tie them together and provide a watertight exterior cladding assembly.

The non-structural panel assembly consists of:

• EPS insulation;
• optional air barrier;
• basecoat;
• mesh; and
• finish.

The EPS insulation has a furring channel embedded in the foam with a sleeve on each end to allow for a mechanical attachment to the substrate. This type of panel is attached to the substrate with a mechanical and adhesive attachment. The lightweight panel type can be installed on virtually any type of project; an advantage in its use is there is no need to modify an existing structure for retrofits and remodels. This panel uses a ship-lap design as one method for joining the panels. A silicone sealant joint can also be placed between the panels to provide a watertight exterior cladding assembly. Non-structural panels are ideally suited for existing low-rise buildings where disruption of the existing business is critical.

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A closed-cell backer rod is required, and the typical width for an expansion joint is 19 mm (3/4 in.). A 22.2-mm (7/8-in.) closed-cell backer rod is installed in a 19-mm wide joint—the specification for the preferred width to depth ratio is 2:1. The sealant joint would have an hour-glass configuration and the backer rod helps to maintain the correct ratio.

The decision to use panels should begin early in the stages of design development. The design professional must determine whether the project is suited for prefabrication. However, not all areas of the project will be panelized—there may be some areas where there is an in-place application depending on tie-ins and connections.

A case study on panelization
The Mayfair Renaissance, a 36-story tower built in downtown Atlanta, was constructed to match an existing precast concrete tower onsite. The panels were built offsite in a controlled environment in Lexington, Kentucky. The controlled environment enhanced quality control, and no days were lost due to inclement weather. Since the panels were manufactured offsite, there were fewer disturbances to the site and reduced construction waste. The lightweight panels reduced the amount of structural steel as compared to the precast, and the panels were also more energy-efficient with a blanket of continuous insulation to reduce heating and cooling costs. Panelization has been a popular method for construction in the hotel industry over the last 30 years since the reduced construction time allows the owner to receive revenue more quickly when compared to a stick-built project.

Specialty finishes
A new development in the EIFS industry was the introduction of finishes with super-hydrophobic self-cleaning properties, rinsing clean with rainfall. A major advantage of the finish is its high resistance to mold, mildew, and algae which reduces maintenance costs. The finish is offered in various colors and textures. A smooth coating is also available to apply over existing EIFS surfaces and other exterior substrates.

EIFS offer specialty finishes that replicate brick, granite, limestone, metal panels, and precast. These finishes are easier to install and can require fewer specialty trades than traditional cladding materials. Specialty finishes offer a cost-effective aesthetic option, increase energy efficiency, and moisture protection. The finishes offer an identical look to the natural cladding, but are less heavy, allowing the creation of a lighter building.

Deflection criteria is the extent to which a material can bend or flex during its lifetime. A cladding with a deflection of L/240 is more flexible than a cladding with a deflection of L/360, L/480, or L/600. Claddings with a higher deflection criteria require a heavier structure to support the weight of the cladding and are less flexible. In other words, since EIFS requires deflection criteria of L/240, and other claddings such as brick and limestone need L/600, an owner can also save on the cost of the structural steel.

The Homewood Suites project in Nashville, Tennessee (currently under construction), is using an EIFS brick and limestone finish. The project was over-budget with traditional brick and natural limestone due to the cladding’s cost and the structure required to hold its weight. Specialty finishes replicating the look of limestone are gaining in popularity due to the cost savings and the ease of application.

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[8]EIFS with a metallic finish—designed to replicate metal panels—offers an expedient and cost-effective solution to metal panels since the material can be installed onsite and adjusted to allow for any changes in framing. The material does not have to be pre-ordered and is offered in various colors. Unlike traditional metal panels, EIFS with a metallic finish has continuous insulation, and there are no penetrations through the cladding for attachment to the substrate.

EIFS testing and research
One of the most important features and benefits of EIFS is the result of independent testing to demonstrate its long-term performance compared to other claddings.

In 2003, DOE contacted EIMA proposing a thorough hygrothermal evaluation of EIFS alongside numerous other commonly used claddings.²[9]

EIMA worked with Oak Ridge National Laboratory to design and construct a specific facility dedicated to this purpose. Testing was performed in two phases, from January 2005 to May 2006 and June 2006 through June 2007.

The Natural Exposure Test (NET) facility, located in Hollywood, South Carolina, is a fully conditioned enclosure designed to accept completely instrumented wall sections. Phase One of the DOE/EIMA study—lasting 17 months—evaluated 15 individual wall sections, including barrier EIFS, EIFS with drainage, stucco, brick, and siding.

In Phase Two, which lasted 13 months, additional wall sections of all claddings were placed on the northwest side of the building, and flaws added to their construction. These flaws allowed water to enter the wall, behind the cladding, in order to test more rigorously the water-resistive barrier components. This data was also monitored and analyzed by the Oak Ridge National Laboratory.

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The ORNL testing at the NET facility demonstrated the following key conclusions:

• EIFS with a liquid-applied WRB, performed better than any other tested cladding assembly—15 individual wall sections that included barrier EIFS, EIFS with drainage, stucco, brick, and siding were also tested;
• EIFS assemblies had superior drainage capability compared with the other claddings as evidenced by the lower relative humidity (RH) values through the various wall components; and
• the best overall performance was an EIFS with 101.6 mm (4 in.) of ci applied over a liquid-applied WRB with an empty (no batt insulation) stud cavity.³[11]

Conclusion
Over the last 50 years, exterior insulation and finish systems have demonstrated they are versatile, lightweight, energy-efficient claddings that can be installed over various substrates. Independent third-party testing has shown EIFS can outperform other types of exterior cladding. Whether field-applied or a pre-fabricated panel, such assemblies can be considered for existing, new, or retrofit projects.

Notes
¹ View the Oak Ridge National Laboratory study results at www.ornl.gov.sci/roofs+walls/research/EIFS/eifs.htm[12]. (back to top[13])
² View the study results at www.ornl.gov.sci/roofs+walls/research/EIFS/eifs.htm[12]. (back to top[14])
³ The full report is available at www.ornl.gov/sci/roofs+walls/research/EIFS/eifs.htm[15]. (back to top[16])

Michael A.DeLaura, LEED AP BD+C, is a 28-year veteran of the EIFS and coatings industry, and is currently an exterior cladding specialist for Sto Corp. DeLaura is an active member of the U.S. Green Building Council (USGBC), and a member of its education review team. He has reviewed proposals for the last three GreenBuilds. He is a board member of the Hampton Roads Green Building Council, and serves on the education and programming committee. He can be reached at mdelaura@stocorp.com[17].

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