Prefabricated EIFS-Clad Wall Panel Assemblies

Designers, contractors, and owners all benefit from this advanced building approach

Architects and general contractors are constantly in pursuit of time-efficient, cost-effective, and quality-assured solutions related to building design and construction. Currently, this objective is even more influenced with the developing skilled labor shortage present in many construction disciplines and markets. An increasingly common solution to address all of these objectives is the use of off-site fabrication of key building assemblies. In particular, prefabricating exterior walls with metal studs and exterior sheathing has been routine practice for many commercial buildings. A growing number of design and construction professionals have recognized that it is also quite possible and advantageous to go several steps further and create more complete wall panels. In fact, many prefabricated wall sections can be air and water sealed to meet code, insulated with continuous insulation to meet or exceed energy requirements, and finished in a variety of appearances. One of the best means to accomplish all of this in an exterior wall assembly is found in using prefabricated wall panel assemblies clad with exterior insulation and finish systems (EIFS). This course addresses, in detail, the characteristics, advantages, and design considerations in using this proven construction approach.

Prefabricated EIFS Panel Overview

Prefabricated panel construction has been around for many years, but the process is still largely misunderstood. Owners, developers, and designers not familiar with prefabrication may wrongly perceive it as a complex, costly, and/or time-consuming process. Without overcoming these misconceptions, they run the risk of not considering all available options and missing out on the potential real benefits of prefabricated construction.

Prefabricated EIFS panels are essentially no different than traditional field-applied EIFS. From an engineering, performance, and code-compliance standpoint, they do everything that field-applied systems do. The only difference is that they are simply fabricated in an off-site shop or in a designated area at or near the construction site in a well-managed and protected manner. Once the panels are complete, they are then delivered or lifted into place onto the building. The fabrication and installation can be done by the same company or different contractors depending on the circumstances of a project.

Prefabricated EIFS panels are designed, detailed, engineered, and completely sealed around their entire perimeter as a full-face sealed wall assembly. Fabricated essentially as a series of performance layers, they provide complete air, water, vapor, and thermal barriers. They can also incorporate drainage capacity in the wall assembly through the integration of fluid-applied air- and water-resistive barrier coatings, integral fluid-applied flashings, and horizontal weep and drainage detailing.

If the finished prefabricated panels are constructed off-site, then their maximum size may be dictated by over-the-road trucking limitations for width, length, and height (i.e., 45–55 long, 8–8.5 feet wide, and 8–8.5 feet tall). This can usually be worked around in most designs, but if large sizes are needed with critical dimensions, then consultation with a fabricator may be in order to determine their practical limits. Panel size for either on-site or off-site fabrication could also be limited by crane-lifting and erection access and capabilities for size, weight, and space availability. Nonetheless, prefabrication is suitable for a wide range of sizes, shapes, and configurations.

Using Prefabrication to Overcome Weather and Temperature Issues

Quality assurance and project time schedules are important aspects of all building construction projects. The most common challenges associated with both are weather, temperature, and the related protection of materials and processes. Field-applied materials, including EIF systems, can be limited by unintentional negative influence from such weather conditions, leading to possible schedule delays. If the temperature and/or weather falls outside the product curing guidelines, then the contractor may need to delay the work or install temporary protection until the materials cure—both of which create unknown and uncontrolled conditions that can add significant cost to a project if not budgeted initially. These conditions may also lead to material defects and void any warranty.

By contrast, when construction is protected from weather and temperature conditions outside of one’s control, the building envelope can be more consistent in quality, more easily meet time schedules, and be more readily coordinated. When prefabricated wall envelope panels are built off-site, or even on-site but indoors in a controlled environment, there is a more predictable production schedule and multiple quality assurance verification points in the process. Within a prefabricated EIFS panel production facility, the temperature is controlled, enabling proper and managed material curing time. Additionally, with no concern for weather conditions, prefabricated EIFS panel production can be completed on schedule despite outside temperature fluctuations or precipitation events. Furthermore, for a great portion of the country, winter significantly impacts all temperature- and weather-sensitive construction. Prefabricated EIFS panel production and erection can occur during the winter months, significantly enhancing building envelope enclosure time objectives and dramatically shortening a project’s overall construction schedule. Overall, prefabricated EIFS panels can be worked on and completed while the building structure itself is underway, allowing for a quicker enclosure and completion of the exterior facade, thus enabling the building to open sooner.

EIFS Panel Design and Construction Considerations

Based on the schedule and quality advantages just described, it is increasingly common to see components of a project prefabricated, including exterior wall portions of the building envelope. Since these enclosure components can be manufactured cost-effectively off-site and easily transported, the on-site work is focused on lifting and attaching the panels to the building structural frame to provide the enclosure for the building. Due to the fairly universal ease and application of this process, prefabricated EIFS panel construction can be used on practically any building but is more commonly used in education, hospitality, health-care, office, entertainment, and multifamily buildings. These buildings tend to be larger in size, have more repeating and rhythmic features that result in duplicating panel designs, and are built under tight timelines. For commercial buildings, they have become favored because a faster construction cycle leads to quicker occupancy.

Architectural Character, Style, and Finish

EIFS claddings have a long-standing history for easily accommodating any architectural character or style. This remains true whether the building uses a field application or prefabricated panels. That means EIFS-clad panels can incorporate quoins, cornices, trim bands, medallions, or grooves, all of which are integrated as components of the panel during the production fabrication process.

While much has changed to enhance EIFS’ performance over the years, the biggest advancement is the availability of a wide variety of finishes. Traditionally, EIFS have been thought to look similar to conventional stucco. Standard finishes are available in almost any color in a rough or smooth finish. Further, sophisticated specialty finish options now allow the EIFS facade to represent the aesthetic appearance of other materials, such as brick, granite, stone, travertine, limestone, metal panels, and even weathered steel. In addition to the appearance, there have been significant advancements in the chemistry and long-term performance of finishes. EIFS’ textured finish can now incorporate a hydrophobic water-repellant enhancement that utilizes both state-of-the-art chemistry and fractal geometry technology to enable a textured finish surface treated to repel water. This allows it to dry faster and reduce the accumulation of airborne dirt and other contaminants, keeping it cleaner longer and reducing maintenance costs. Additionally, there have been significant advancements in enhanced UV-stable colorants, raising the bar for color science to a whole new level of stability, resistance to UV degradation, and long-term color brightness, and paving the way for the use of many colors not previously considered.

Design and Engineering Process

The design process using prefabricated EIFS panels is very straightforward and consistent with most typical design sequences. The architect determines the aesthetic and performance requirements in accordance with the overall design intent of the building envelope. Panel layout and engineering design for the framing can be done in concert with a structural engineer or with a specialty engineer for prefabricated EIFS panels. Either way, the panel engineers coordinate with the fabricator and/or erector, perform the final detailed engineering for structural performance, and develop the panel connections. They also provide the fabrication engineering calculations required to meet the building’s wind, dead, and live design loads. Since EIFS panels are among the lightest prefabricated panel options available, they allow for reduced structural capacities for materials to be used in the panels, which will reduce building dead loads and overall building structural cost. The panel engineers also create the detailed shop drawings specific to the overall panel size and configuration in accordance with the architect’s building design and desired exterior aesthetics. Once the architect reviews and/or approves the shop drawings, then fabrication begins.

Quality Control

By employing a specified prefabricated panel process, architects as well as building owners can be assured that the exterior wall will be completed correctly and with no substitute products. Additionally, the architect can readily inspect, monitor, and observe the prefabricated EIFS panel wall system’s quality off-site during fabrication and before it is placed on the building. This is a very important quality-assurance measure that is not usually available with traditional construction methods where the exterior wall is constructed directly on-site, occasionally in difficult-to-access areas, with numerous steps, layers, materials, and trades.

Storage and Staging Space

Storage and staging space can be extremely limited on job sites. Prefabricated EIFS panels made off-site do not require any on-site production area, staging area, or on-site storage space. Of course, they can be assembled on-site if a suitable area and protection are available. Either way, they are typically crane-lifted into place directly off of a truck or a designated place on-site. Sometimes, that means the sharing of an already available on-site crane is possible. This lends itself to panels being installed at night or other off-crane hours, thus making full use of the crane’s availability and sharing cost.

Using this process, prefabricated EIFS panels can be shipped on a “just-in-time” basis, erected, and installed the same day. No scaffolding is needed, which assists sites with limited space and helps control costs. Prefabricated EIFS panel construction also limits the number of subcontractors and bodies on the job site, along with reducing or eliminating job site waste from the assemblies. The entire panel consisting of framing, sheathing, air- and water-resistant barriers, continuous insulation, and aesthetic finish is fabricated and then installed by one subcontractor with a small crew, compared to the multiple trades that are required with more traditional field construction methods and far more on-site labor.

Building and Energy Code Compliance

Since their introduction to the U.S. market in 1969, EIFS have evolved into one of the most tested and well-researched wall claddings in the construction industry. Today’s EIFS are in full compliance with building codes which emphasize weather protection, energy conservation, and fire-resistive construction and performance. These codes include the International Building Code (IBC), the International Energy Conservation Code (IECC), ASHRAE Standard 90.1, and other related standards.

Recent updates to the IBC require water-resistive barriers and full-assembly fire testing for exterior walls, which prefabricated EIFS panels can provide. Further, the IECC latest requirements for continuous air barriers and continuous insulation have made exterior wall assemblies far more sophisticated not to mention thicker in their composition. Coupled with enhanced requirements for flashing integrations, these code changes are fueling an increased concentration toward dramatically improved energy efficiency compared to the past. Of course, many of these changes are impacting overall building structural cost that could be offset by the significantly lighter weight of a prefabricated EIFS panel wall assembly.

Most notably, the IECC has dramatically increased the requirement for exterior continuous insulation (CI) on commercial-framed wall assemblies as a means of mitigating heat energy gain/loss through thermal bridging at the stud lines. These new criteria alone add two or more inches of depth to a traditional veneer wall assembly. Adding CI also pushes the cladding or veneer off its normal structural plane, which can significantly increase bearing structure, anchoring, and attachment needs, additionally increasing cost and possibly effecting long-term cladding performance.

Traditional EIFS as well as prefabricated EIFS panels have always been an energy-efficient cladding. This energy efficiency is attributed to the continuous insulation and air barrier used as components of the system. EIFS continuous insulation wraps the exterior of buildings eliminating the thermal bridging that occurs when traditional cavity insulation is installed between the framing studs. While traditional cavity insulation has a stated R-value, the effective R-value of the total assembly is actually much lower. For example, a building with steel studs at 16 inches on center that uses cavity insulation rated at R-13 has an effective value of R-6 due to thermal bridging. This dramatic reduction comes about because heat is transferred through the studs of the wall, completely compromising the cavity insulation. Continuous insulation installed outside of the studs overcomes that thermal bridging issue and is much more effective in terms of energy performance.

Fire Safety

While many cladding products can be code compliant with modification, EIFS are completely code compliant unto themselves. Traditional EIFS as well as prefabricated EIFS panels have been tested in a variety of typical wall assembly configurations and have successfully passed the stringent NFPA 285 flame-propagation test as well as the ASTM E-119 2-hour load-bearing wood-frame assembly test.

Air- and Water-Resistant Barriers

Prefabricated EIFS wall panels are highly unique in that they are composed of all the building, and energy-code-required barrier layers, including an integrated air- and water-resistive barrier (AWRB) in addition to the continuous insulation (CI). The majority of EIFS manufacturers offer fluid-applied AWRBs that also contribute to the development of a drainage plane in wall assemblies. The AWRB can be applied via trowel, roller, or airless sprayer depending on the contractor’s preference or underlying substrate requirements. Further, they are available in either a permeable or nonpermeable vapor barrier version depending on the hygrothermal performance needs of the overall wall assembly. Part of the beauty of a prefabricated EIFS panel assembly is that since there are no through wall mechanical attachments, no punctures are created in the AWRB. That means there are fewer opportunities for air and water to infiltrate or cause damage.

Prefabricated Panel Types

With an understanding of the basic principles and makeup of prefabricated EIFS panels, let’s take a closer look at how they are physically constructed. Essentially, there are three common types of fabrication techniques, each of which are explored further in the following paragraphs.

Full Steel-Stud Composite Panels

The most common type of prefabricated EIFS panel assembly has traditionally been a full steel-stud composite panel system. These very complete panels are composed first of steel-stud framing covered with exterior sheathing. Next, AWRBs and flashing for rough openings or wall penetrations are installed to create the needed air and water resistance. Then, adhesive, and continuous insulation boards are installed on top. Finally, a reinforced base coat is applied followed by a selected textured finish coating. This panel type represents one entire exterior wall envelope assembly with the full combination of multiple trades, materials, and their necessary coordination.

Full steel-stud composite panels are very flexible in regards to orientation and size, with the only size restrictions being those of trucking capabilities, roadway or delivery route restrictions, site logistics or access and erection requirements. They are commonly fabricated in sizes ranging from 8, 10, or 12 feet wide and up to 50 feet long depending on the trucking arrangement used. Full steel-stud composite EIFS panels are typically designed and fabricated with barrier or non-drainage type EIFS claddings; however, drainage capacity can be incorporated on an individual-panel basis. This would require the development of weep detailing at horizontal termination conditions, such as the head joints of wall-penetration components like windows, doors or louvers as well as at the bottom horizontal panel joint. Because this panel type includes the metal studs and sheathing, it has complete and inherent structural integrity. Typically, it is the EIFS panel fabricator who coordinates the detailed design and engineering of the panels and structural connections in accordance with the architectural drawings and specifications.

Framed openings for windows and other envelope components can be designed into the panels, and, in many cases, those components can be integrated and preinstalled within the panel.

Full steel-stud composite panels represent a collection of wall envelope components that are independent of each other but function as one. Once the panels are shipped to the job site, they are put in place using a crane and welded or mechanically fastened to the existing steel frame or prepared slab edge of the building structure. Traditionally, full stud composite panels are designed and installed in a “balloon framing” manor that extends past multiple floor plates, dramatically simplifying and accelerating building envelope construction. This approach provides continuous insulation across the floor slab edge and overcomes another thermal bridging condition. It also moves the metal framing outside of the slab edge, creating more usable interior square footage which may translate to increased lease revenue for a building owner. As in all balloon framing situations, however, fire stopping and sealing at floor slab edges may be required to prevent vertical spread of fire in the assembly.

Alternatively, full steel-stud composite panels can be installed in a “platform framing” process where the metal framing for each story rest on the floor structure. Treatment of the slab face can be addressed in several ways. Either platform or balloon framing allow large and intricate panel designs to be quickly and easily incorporated onto the building’s exterior, which is the hallmark of what prefabricated EIFS panels can accomplish.

Galvanized Corrugated Steel-Deck-Backed Panel

A second and unique panel fabrication option uses EIFS applied to a galvanized corrugated steel decking substrate with a galvanized steel channel perimeter framing. This option is most ideally suited for rooftop screen walls around mechanical equipment or other similar conditions that need attention to control the overall building appearance. This fabrication allows for the backside of the panel assembly to be left exposed to the weather and elements but can be styled and finished on the front to match the remainder of the building’s architectural character. This panel option does not require a sheathing layer substrate, and the EIF system is attached directly to the steel deck using mechanical fasteners. These types of panels are usually much lighter and thinner than the traditional full steel-stud composite EIFS panels, which make them much easier to transport and install onto an open structural column and beam frame. Steel decking substrates are generally non-loadbearing and would therefore require additional framing support for windows, doors, louvers, or other wall-penetration components. Corrugated steel-deck-backed panels are available in sizes comparable to full steel-stud panels.

Lightweight Channel-Reinforced Insulation

One of the most unique prefabricated EIFS panel options is a simple, lightweight, channel-reinforced insulation panel. Lightweight EIFS panels do not include all of the integral framing, sheathing, or structure needed for other EIFS panel types. Therefore, they require that a wall assembly and substrate are in place to which the panels can be attached, making them particularly well-suited for retrofit or renovation construction projects. As a result of their reduced structural makeup, these panels are generally smaller in size at approximately 10 feet by 12 or 14 feet, making them lighter in weight and easier to install. In this type of panel, metal hat channels are inserted and glued into the back of expanded polystyrene (EPS) continuous insulation board to give it added structural stability during handling and erection. Once the panels are completed and the EIFS is cured, they are brought to the job site and installed onto a new or existing wall substrate using either an adhesive, mechanical fastening, bearing clips, or a combination of the three as determined through engineering. The new or existing substrate can also be prepared with the EIFS manufacturer’s fluid-applied AWRB barrier coating, allowing the panels to be installed as a moisture drainage assembly.

It should be noted that lightweight, channel-reinforced insulation panels type are ideal for both new and retrofit constructions. In new construction, they allow a quicker installation of the facade system compared to other systems. For retrofit situations, their lightweight nature means that the existing building structure can likely accommodate the new system easily, while their thin profile means they can integrate with existing building systems and set back requirements. Additionally, the concept of lightweight channel-reinforced EIFS panels can be applied to smaller shapes that are made of coated and finished EPS insulation. Such shaped sections can be fabricated and installed as a building feature, such as a new cornice or raised band onto an existing facade surface.

Panel Joint Treatment

Regardless of the panel type used, joints between panels need to be addressed. EIFS were originally designed and engineered as a face-sealed cladding assembly, meaning that all edges need to be properly sealed so no incidental moisture can pass through or around the edge of an EIFS cladding. This original, inherent engineering feature remains in place for current EIFS claddings, including prefabricated panels. In the case of prefabricated EIFS panels, most EIFS manufacturers will provide a list of sealants that have been tested and approved for compatibility. Also, most sealant manufacturers will perform project-specific compatibility testing if required.

Different EIFS panel types will have different criteria respective to panel joints. Full steel-stud composite panels have panel joints that generally extend through the full wall thickness. For this panel type, it is good design practice to include a double line of sealants at these panel joint locations. This double joint will be comprised of two individual backer rod and sealant joints set one on top of the other, providing redundancy in the event of a breach of the outer layer. This allows the owner time to repair the breach before water can penetrate into the interior of the building. It also eliminates UV exposure of the inner seal and can be configured to accommodate drainage within the joint itself.

Sealant joints should be properly designed for joint width, depth, and modulus of elasticity to specifically accommodate the expected movement between panels without overstressing the materials. A good rule of thumb is to design the sealant joint width to be not less than four times the expected movement and not less than ¾ inch. Seismic requirements may be larger. Some fabricators also incorporate a gasket system to seal panel to panel joints. Always verify with the manufacturer that the selected sealant or gasket has been tested for compatibility and can accommodate the expected movements.

One other consideration is the option of using horizontal shiplap joints in panels. This is especially appropriate in lightweight channel-reinforced panels that can be shaped to form the upper and lower shiplap profiles. The advantage of this approach is a significantly reduced lineal footage of sealant with less maintenance potential. A shiplap joint may still have sealant or a compression gasket, but it would all be concealed and not exposed to UV or other degrading elements.

Conclusion

Prefabricated EIFS wall panel construction brings together the advantages of using the latest EIFS technology with prefabricated panel construction techniques. EIFS provide code compliance and energy conservation through the integral layers of insulation, AWRBs, and sheathing. The continuous insulation overcomes thermal bridging, wrapping the building in an insulation blanket. Using lightweight EIFS instead of heavyweight claddings, such as brick, stone, precast, etc., can reduce the sizes of structural members thus reducing structural loading and cost. The capacity to convey architectural style and the expanded breadth of finishes provides the architect with many choices to help achieve design goals while providing stunning details and shapes with ease. Prefabricated EIFS panel construction provides architects peace of mind through higher-quality assurance standards that are backed by an extremely comprehensive warranty. Prefabricated panel construction allows for quicker construction timelines and results in the building opening sooner. Overall, prefabricated EIFS wall panels offer more as a single-sourced assembly than any other prefabricated wall panel assembly.

Peter J. Arsenault, FAIA, NCARB, LEED AP, is a nationally known architect, consultant, continuing education presenter, and prolific author advancing building performance through better design. www.pjaarch.com, www.linkedin.com/in/pjaarch