Insulated Composite Backup Panels  

Exterior walls have always been a key element of the overall building envelope to define the separation between indoor and outdoor space. In its earliest forms, solid masonry and stone provided this function but as lighter-weight materials such as steel emerged, new exterior wall systems made of multiple components became commonplace. In recent years, the importance of energy conservation and green building design has focused increased attention on the details of how these exterior walls are designed, assembled and actually perform in numerous ways. This attention has created new options for how walls are constructed using improved products that address all of the performance issues of exterior walls. One of the most versatile and promising products now available in support of this focus are insulated composite backup panels (ICBPs).

Conventional Wall Systems

All exterior wall systems need to address some fundamental design and performance issues. Obviously, they need to provide structural support either for the building or simply for the wall itself if attached to a separate structural system. As the dividing line between inside and outside, exterior walls need to act as the barrier to weather, wind and rain, and still offer a suitable finished appearance. Since the air pressure between inside and outside is typically different, and since air will naturally flow from high pressure to low pressure, the wall needs to address and control this air flow. That air will commonly carry vapor with it, which, if not controlled, is prone to be captured in the wall, condense and cause damage over time. Similarly, heat will flow from warm areas to cold areas and exterior wall designs have increasingly paid attention to effective insulation techniques to address that heat flow thus improving comfort while reducing the amount of energy used in buildings to maintain that comfort. Hence, the performance of any exterior wall system can be evaluated on the basis of how well and how completely it addresses all of these fundamental issues and needs. This is particularly true for the following conventional wall types.

Photo courtesy of CENTRIA

Solid Masonry Walls

Solid multi-wythe brick walls were the norm for centuries for exterior wall construction. This was followed by a variation of brick applied directly over poured concrete or concrete masonry. As solid construction, these walls were durable and long lasting from a structural standpoint but offered little if any thermal resistance to heat flow. Their shear mass made them an effective air barrier, but they were often porous and prone to wicking water and moisture into parts of the walls. Hence they were not always an effective barrier for water and vapor, particularly if maintenance was lacking.

Masonry cavity wall construction is intended to allow water and moisture to collect and drain away between the exterior brick rain screen and the interior back up wall. Image courtesy of CENTRIA

Masonry Cavity Walls

Masonry walls that separated the inner and outer wythes by an air cavity have become commonplace as a means to improve performance compared to solid walls. In this approach, a layer of finished brick or other masonry is located on the outermost side providing the aesthetic appearance and acting as the weathering surface or “rainscreen.” The intentional air cavity behind this outer masonry separates it from an inner or back-up layer of masonry or concrete, which is often the primary structural component as well. The cavity exists to allow moisture that may enter and get trapped in the assembly to collect and drain out through weep holes at the bottom. This drainage usually occurs on the outer face of the inner masonry wall, thus creating a drainage plane there. That inner masonry wall then becomes the basis for the barrier for air and vapor penetration between inside and outside. Thermal insulation is commonly added within the cavity, thus improving the thermal performance of the assembly, although metal brick ties often interrupt or interfere with the effectiveness of that insulation.

Conventional metal framed composite walls are assembled from many separate components that are installed on either side and between metal studs. Image courtesy of CENTRIA

Steel Framed Walls
With the advent of steel framed buildings in the late 1800s, new wall assembly options were possible for commercial, industrial and institutional buildings. Buildings became lighter in weight compared to masonry buildings and could be assembled with multiple manufactured components. This included the eventual use of steel studs for infill between structural steel members or as the structure itself for a low-rise building. This system provided great flexibility in design, less dependence on weather or season for installation, and a predictable quality from the manufactured steel products. The steel framing of course then needed to be covered or filled in to address air, water, vapor and thermal issues. That means that multiple products are added by various labor trades to include interior drywall, vapor barriers, insulation, exterior sheathing, building wrap/ air barriers, and exterior finish. The hoped for result is that the outer side of the steel framed wall is water and air tight, while the climate appropriate side is also vapor tight. In addition the thermal insulation needs to be consistently and uniformly installed and functional to achieve its full thermal resistance capability. Since all of this is done in the field under varying conditions and with varying degrees of installer capabilities, it is understandably very difficult to achieve consistent construction of a wall that will perform optimally.

Addressing Conventional Wall System Design Issues

Designing with conventional wall systems with the intention of achieving high performance in all areas, means that the weaknesses of common multi-component wall assemblies must be overcome.

Multiple Penetrations

One of the most obvious problems is the presence of multiple penetrations from hardware and fasteners through any of the air or vapor barriers. Hundreds if not thousands of such fasteners are used to hold interior drywall and exterior sheathing in place and in the process typically puncture the barrier membranes that are otherwise so painstakingly installed. Further, masonry ties or metal panel clips are connected through the exterior sheathing and air barrier into studs to secure the finished facing or rainscreen material in place.

Multiple fasteners and penetrations that need to be covered and sealed compromise the integrity of air, water, and vapor barriers in multi component conventional wall systems. Photos courtesy of CENTRIA

 

Unless each of these penetrations are sealed, they are potential spots of failure that allow water, vapor or air to pass through, thus reducing the performance and efficiency of the wall or worse, causing damage to occur in the wall. This damage could include such things as direct water penetration that compromises materials like gypsum board or insulation or could lead to longer-term problems such as rusting of steel members, mold growth or loss of thermal performance from wet insulation. None of these are desired outcomes of course, but correcting them often becomes a confusing matter of blame between contractors and different subcontractors over the flaw that caused the problem, and likely citing the design as a potential source of failure as well.

Sealing Points of Weakness

Other sources of performance loss in a conventional stud frame wall include mechanical and electrical boxes that are run in the wall, thus causing a breach in the inner seals and reducing the available insulation between the studs. The actual wall framing is also interrupted by floor and roof slabs or decks similarly causing an interruption in the air, water and vapor barriers. In all of these locations, the barriers must be designed and installed to be continuous around these potential points of performance weakness. This attention to sealing is important not just for the integrity of each of these barriers, but also to reduce heat loss or gain from excessive air infiltration. The latest versions of energy codes and the recently released International Green Construction Code (IgCC) in particular, all recognize the importance of such barriers and have them mandated for inclusion in wall assemblies. They also require that they are appropriately sealed at all junctions and penetrations as described.

Codes and Standards

Energy codes and green building standards have also recently recognized that insulation installed between studs, particularly steel studs, has real limitations. The thermal resistance value of insulation shown by its manufacturer is likely reliable for the insulation itself. However, the actual value for the composite assembly will be less, often a lot less. This is due to the significant thermal bridging or short circuiting of heat flow through the steel studs. ASHRAE Standard 90.1 which is appended to many energy codes and other standards include some very clear correction factors for this phenomenon. For example, a metal stud wall using 6-inch nominal studs at 16-inch o.c. may include batt insulation that carries a manufacturer's rating of R-21. However, the frequency of the metal studs including the head and track pieces compromises that R-value by as much as 65 percent. Therefore AHSRAE 90.1 assigns a working value for the assembly of only R-7.4 (U-value of 0.135) which is little more than a third of the intended R-value. At this level it does not meet the minimum energy performance levels required to be code compliant in most of the U.S.

Effective R values of steel stud wall assemblies with insulation installed between the stud framing per ASHRAE 90.1. Source: CENTRIA

 

Insulated Composite Back-up Panels (ICBPs) are based on metal exterior panel and rainscreen design principles. Photo courtesy of CENTRIA

Recognizing the limitations of cavity insulation between steel studs, an alternative has been incorporated into most energy codes and standards based on an application of insulation that is continuous on the outside of the studs. This continuous insulation is commonly a rigid foam plastic product of one type or another which may also serve as a water barrier and drainage plane if designed to do so. In some cases, it may act as an air and vapor barrier as well. To use the insulation in any of these ways will require proper attention to junctions and joints to be sure they do not allow water or air to penetrate. Even if that is accomplished, achieving truly continuous insulation is difficult in that it requires near perfect installation and even then is compromised by penetrations from supports and fasteners. Those fasteners, which may be “Z”-shaped channels to hold the insulation in place, also compromise thermal performance by creating a thermal bridge at each of those junctions. Separate fasteners that support the exterior rainscreen or masonry veneer will commonly need to penetrate the insulation and compromise its integrity and performance even more.

A further criterion of any wall assembly that uses foam plastic insulation is fire protection since these products can not only be highly flammable, they can give off toxic smoke. The International Building Code (IBC) requires that wall assemblies be tested for temperature and flame propagation. If a continuous insulation assembly is specified or designed, it must demonstrate that it complies with the IBC and passes testing of the National Fire Protection Association (NFPA) based on NFPA 285.

Clearly, there has been great attention paid to improving performance in the evolution of opaque wall assemblies. All of this has set the stage for other innovative alternatives to be researched and implemented that can provide the desired performance and overcome the weaknesses described here of multi-component conventional assemblies.

The Emergence of Insulated Composite Backup Panels (ICBPs)

Based on all of the previous work and understanding of exterior opaque wall systems, an ideal view of a high-performing wall that meets current needs can be envisioned. Inherently, it must provide a continuous, unbreached, air, water and vapor barrier. Thermally, it should provide a full covering of rigid insulation outboard of wall studs to avoid thermal bridging and free up the stud cavities for other needed things like mechanical and electrical boxes. From an energy performance perspective, it would provide superior thermal performance reliably in all climates. The materials of this ideal wall would be waterproof but non-organic so that no mold would be allowed to grow. And of course it would need to comply with all relevant building and fire codes and the associated testing for compliance. From a design standpoint, it would offer exterior finish options, be durable but lightweight to minimize structural requirements, and maximize the potential for meeting green building design criteria. From a construction perspective, this ideal wall assembly would limit the potential for installation errors through simplified design and install quickly by minimizing the number of trades involved, thus clearly identifying lines of responsibility for performance. Building owners of course would want to know that they were receiving an excellent value for the installed cost of such a system and its life-cycle costs were attractive.

Although no system is perfect, a wall assembly that uses ICBPs along with metal studs on the interior and a separate rainscreen on the exterior comes very close to achieving this idealized vision of a wall assembly. As a recent addition to the choices available they are already proving to be superior in providing advanced thermal performance and moisture control compared to conventional wall systems.

ICBPs were spawned by product manufacturers who were in the business of making primary exterior metal panels with an insulating foam plastic core. Sometimes referred to as “sandwich panels,” they have been used around the world as an exterior finish system attached to the building structure. This technology has been proven and in use for over 50 years so the techniques of using insulated metal panels are quite well refined at this point. By using this same basic panel technology combined with the latest needs and research for exterior walls, ICBPs were born. Similar to architectural metal wall panels, ICBPs use steel skins sandwiched over rigid insulation. However, as backup or secondary panels that are not directly exposed to sun or weather, they are engineered with lighter-gauge steel, and a more economical coating system. The insulation is selected for greater thermal performance rather than structural performance, meaning that it is less dense. The front and back metal faces of the ICBPs are thermally broken from each other along the top and bottom by the insulation, meaning that thermal bridging is eliminated. The ICBPs are also commonly manufactured in standard sizes with an interlocking, offset lapping configuration for easy installation and sealing.

A steel stud wall assembly with insulation installed between the stud framing. Image courtesy of CENTRIA

As part of an overall wall system, ICBPs are a single component panel that combines four functions within itself: an air barrier, water/vapor barrier, an exterior drainage plane and building insulation. They are intended to be located over the exterior side of metal studs, meaning that typical structural systems and infill framing can be used. Their location and combined functions mean that the wall assembly is no longer dependent on the interior surfaces for air and vapor barrier protection. Hence, the inside face of the studs can be finished with gypsum board or any other interior finish product as desired—penetrations in the interior finished surface will no longer impact performance. It also means that the stud cavities are not required for insulation so any mechanical or electrical runs can be made in that space without impacting the thermal or other performance characteristics of the wall. As such, standard-size smaller studs (e.g. 3-5/8 inches) may be all that is needed instead of deeper studs (e.g. 6-inch nominal) since the insulation is no longer dependent on stud depth.

Factory fabrication of ICBPs means that their quality is more consistent and more readily controlled. On-site installation is commonly done with a simple clip attachment system that holds the panels onto the studs with a minimum of penetrations. In fact, some manufacturers have refined that attachment system to the point that the clips are multi-functional in design—they hold the panel to the studs and extend outward to provide a connection point for masonry ties or other rainscreen materials.

ICBPs are installed on the outside of metal studs and secured into place with a pressure equalized clip fastener that can also be used to connect the rain screen. Photos courtesy of CENTRIA

Further, since they can be installed on the outside of at least part of the insulation, they avoid creating a thermal bridge. When installed in this manner, the panel penetration occurs within pressure-equalized joints so that air and water penetration is avoided. The panels themselves typically contain a factory-applied sealant which is “married” to or connects with a continuous bead of field applied non-skinning butyl sealant at the vertical panel joints. Hence, the entire perimeter of the ICBPs is provided with a continuous air and water barrier seal in addition to the non-permeable properties of the panels themselves. If installed in this manner, the panels can actually be field tested with an exterior water spray test. When subjected to 30 to 35 psi of water spray over at least 5 feet of joinery for at least 5 minutes, no visible leakage should occur through the panels. Once that test is completed, then the rainscreen is ready to install.

Many different rainscreen options can be installed over ICBPs including metal finish panels (left) and brick masonry (right) using appropriate connection techniques secured to ICBP clips. Images courtesy of CENTRIA

 

Rainscreens are meant to be just that–a screen that keeps the initial forces of nature (rain, sun, wind, etc.) off the building. Rainscreens are not meant to be water tight, the back-up system is—in this case, the ICBPs. That means that any rainscreen of choice can be designed or specified for any given installation such as masonry, metal, terra cotta or other available products. Installation is made with connectors such as masonry ties or panel connectors that tie back in to the extended portion of the clip connectors of the ICBPs. Any water that penetrates the rainscreen simply runs down the face of the ICBP which is now the continuous drainage plane for that purpose.

As a manufactured product designed to be installed in a consistent and predictable manner, ICBPs have been tested for compliance with building and fire codes for rigid plastic insulation. In order to be commercially available, manufacturers will readily provide written evidence of passing that testing. Hence, it is entirely appropriate to specify submission of test results as part of the submittal process for any project where these panels are used.

The ultimate result of working with ICBPs is that the design and construction of a simplified wall system is achieved that provides excellent thermal efficiency, advanced moisture protection and vastly reduced potential for failure. They also use fewer components and less labor to install, thus increasing construction efficiency and making them cost effective.

A water spray test at specified pressures for at least 5 minutes along ICBP joints should yield no water penetration. Photos courtesy of CENTRIA

 

Green Building Contributions

The green building movement in this country has given rise to quantifiable rating systems that seek to establish specific levels of achievement in the creation and performance of green buildings. The best known of these green building rating systems has been developed by the U.S. Green Building Council and known as the LEED® rating system. This is actually a family of ratings that applies to different building situations (e.g., new or existing buildings, core and shell, interiors) and in some cases building types (schools, healthcare, retail, homes, etc.).

All of the LEED rating systems have been subject to ongoing changes and updates since their inception, but the basic categories of defining green buildings have remained the same across the different versions over time. With that in mind, the contributions that ICBPs can make fall into several green building categories.

A completed exterior wall system using ICBPs can provide significant contributions to green building design and performance. Image courtesy of CENTRIA

 

Optimize Energy Performance
As mentioned earlier, ICBPs can be specified in several thicknesses which relate directly to their insulating value. Commonly 2 inch thick panels rated at R-14 and 3-in. thick panels rated at R-21 are available. When installed outside the studs they are not subject to the correction factors of stud cavity insulation and therefore provide superior performance. When calculating actual wall assembly performance, nonetheless, the overall U-value of the entire assembly should be looked at. In most cases, wall assemblies with ICBPs will perform notably above the minimum required levels in ASHRAE 90.1 and other baseline standards to demonstrate contributions toward better energy performance of the building.

Materials and Resources

Steel building products are commonly manufactured from recycled content that is derived from pre-consumer and post-consumer sources. In the case of ICBPs the steel used can similarly contain recycled content from both of these sources. Since there will likely be a fair amount of panel material in a building, this could mean a significant contribution toward achieving high recycled content in the total building. Of course, the gauge of the steel and the size of the panel will influence the calculations, but the panels overall can commonly be calculated to achieve at least between 15 – 25 percent recycled content calculated by weight. The specifics should of course be verified with the ICBP manufacturer. At the end of the life of the panels or of the building, the ICBPs can potentially be removed and re-used in other buildings. Alternatively, they can be disassembled with the steel and insulation each being recycled into other products.

Beyond recycling, the single component nature of the panels limits or reduces scrap and construction waste on site. The standardized sizing also helps in this regard. Further, since ICBPs are manufactured in the USA that means regional material contributions are also possible.

Indoor Environmental Quality

ICBPs are pre-finished and require no additional painting or coating in the field. That means that the use of any VOC containing paints or coatings are eliminated. Further, low-VOC sealants can readily be specified for the panel installation thus contributing to maintaining a positive indoor environmental quality.

Innovation in Design

Because of the innovative nature of the ICBPs, some manufacturers have gone forward and received cradle to cradle certification for their products making them exceptional contributors to green and sustainable design. If such a product is specified, then this certification can demonstrate contributions to innovation credits. Additionally, these long lasting products demonstrate favorable life cycle analysis while their lightweight and simplified nature reduces transportation weight and embedded energy.

ICBPs are manufactured in standard interlocking profiles and in standard sizes to make installation easy and cost effective. Image courtesy of CENTRIA

Conclusion

ICBPs represent a significant contribution to the evolution of exterior wall design. Their single-component fabrication takes the place of four separate materials which speeds installation, reduces installation errors, and saves time and money. They have been shown to provide superior tightness as a barrier to air, water and moisture since the materials are unaffected by water and penetrations are limited by integrating attachments.

Further, they provide rigid building insulation at specified levels that is located outside of metal studs to meet the thermal requirements of current energy codes and green building standards in all climates. The single source responsibility of all of these critical performance components means that they can reliably meet stringent fire codes by providing evidence of successful and replicable testing. In short, they are worth consideration on any building project that uses metal framing as viable and superior alternative to conventional wall construction.

Ten years ago everyone was skeptical of moving the insulation outboard of the studs. That construction now has widespread acceptance. Similarly, I predict in the next few years that the insulated metal composite back-up wall system will be widely accepted and used as a superior solution. - Michael Gurevich, Consultant, New York City Brickwork Design Center.

Case Studies

Sherwood Middle School Shrewsbury, Massachusetts

ICBPs being installed at Sherwood Middle School and then covered with a finished metal rainscreen for a very successfully completed exterior wall system. Photos courtesy of CENTRIA Building Type: Education, Middle School Building Owner: Shrewsbury Public School District, Shrewsbury, MA Architect: Lamoureaux Pagano Assoc. Architects, Worcester, MA General Contractor: Gilbane Building Company Providence, RI Dealer/Installer: LYMO Construction Merrimack, NH The $37-million, 130,000-square-foot Sherwood Middle School will offer a modern learning environment to approximately 1,000 fifth and sixth graders in the Shrewsbury Public School system. Slated to open in November of 2012, the new building takes center stage in a sprawling campus that features the former Sherwood Middle School and the refurbished Oak Middle School. The project offers the latest advancements in K-12 educational facilities, including art and music suites, common rooms, physical education space, a dual-purpose cafetorium, nurses’ quarters and a media center—surrounded by small clusters of general classrooms and special education resource rooms to create an intimate, flexible learning space. Designed by the experienced architectural team of Lamoureux Pagano Associates Architects, Inc., the Sherwood Middle School project was constructed with the highest principles of sustainable design, on-site optimization and state-of-the-art engineering and technical systems. The architects placed equal focus on quality and value—the crux of Lamoureux Pagano’s building philosophy. “With an educational facility, there is no single factor that determines our design choices, but rather a number of equally important considerations—aesthetics, thermal value, weather resistance, installation time and budget,” said Katie Crockett, AIA, Project Architect at Lamoureux Pagano Associates Architects, Inc. “Each of these aspects played a key role in the Sherwood Middle School project.” Beneath the attractive mixed-medium exterior of Sherwood Middle School is over 66,000 square feet of insulated composite backup panels, boosting the project’s thermal value and providing a second line of defense against the harsh weather conditions of America’s northeast. While the 3-inch panels boast a considerable R-value of 21, building designers were more impressed with the product’s unique, single-component construction, eliminating the need for separate batt or board installation, exterior gypsum, air barriers, vapor retarders and building wraps. As Principal Architect and President of Lamoureux Pagano Associates Architects, Inc., Mike Pagano, AIA, knows firsthand the value that this system brings to a project. Pagano’s firm was one of the first in the nation to utilize this improved technology. “As early adopters of insulated composite backup panel technology, we are well aware of the performance enhancements these kinds of products can lend to the building envelope,” Pagano noted. “ICBPs are unique because they offer a single-component design, eliminating the need for multiple installation steps and saving us valuable time and money. In fact, they are one of the reasons why we’re ahead of schedule and under budget.”

 

Cardiovascular Consultants Medical Office Building Cape Girardeau, Missouri

ICBPs were used behind the masonry rainscreen of this professional medical office building for superior performance and excellent aesthetics. Photos courtesy of CENTRIA Building Type: Educational, post-secondary school Architects: SRG Partnership, Inc. Contractors: Lease Crutcher Lewis System used: Insulated composite back-up panels that allowed different rainscreen attachments based on different support systems attached to the supporting clips of the ICBPs. Panel Width: 36” [914mm] Panel Length: 12’ [4m] or 20’ [6m] standard lengths Face and Liner: Face – 29 gauge galvanized steel with clear coat finish Liner – 29 gauge galvanized steel with primer Foam Insulation: Minimum 2.4 PCF Urethane modified polyisocyanurate foam. Two inch panels provide an R-14 insulation value while three inch panels provide an R-21 insulation value.

 

Chemeketa Community College Health Science Complex Salem, Oregon

ICBPs were used behind the combination rainscreens of metal and terra cotta at this new complex on the Community College campus affording excellent value and appearance backed up with superior performance. Photos courtesy of CENTRIA Building Type: Educational, post-secondary school Architects: SRG Partnership, Inc. Contractors: Lease Crutcher Lewis System used: Insulated composite back-up panels that allowed different rainscreen attachments based on different support systems attached to the supporting clips of the ICBPs. Panel Width: 36” [914mm] Panel Length: 12’ [4m] or 20’ [6m] standard lengths Face and Liner: Face – 29 gauge galvanized steel with clear coat finish Liner – 29 gauge galvanized steel with primer Foam Insulation: Minimum 2.4 PCF Urethane modified polyisocyanurate foam. Two inch panels provide an R-14 insulation value while three inch panels provide an R-21 insulation value.

 

Goose Creek Correctional Center, Anchorage, Alaska Wasilla, Alaska

The location and the use of this building were very demanding requiring high energy performance combined with quick, reliable construction processes. Photos courtesy of CENTRIA Building Type: Government, correctional center Architects: HOK Contractors: Neeser Construction The architect of this demanding project wanted to use an insulated wall system that would not sacrifice energy efficiency in the harsh Alaska winter. ICBPs were selected because they eliminated thermal transfer through the steel studs providing much better overall wall U-values. In addition, a pressure equalized rain screen system was designed and installed – a must in extreme climates such as this one.

 

New York Power Authority Niagara Office and Warehouse Lewiston, New York

ICBPs were used on this large warehouse and office building located in a cold climate. Both metal and masonry façade materials were installed in front of the ICBPs creating the desired appearance and high performance. Photos courtesy of CENTRIA Project type: Office and warehouse Architects: Nelson & Associates Engineering Contractors: SRL Contracting and Service Company System used: Insulated composite back-up panels that were combined with the appropriate support system for either metal panel or masonry on the exterior. Panel Width: 32” [813mm] Panel Length: 12’ [4m] or 20’ [6m] standard lengths Face and Liner: Face – 29 gauge galvanized steel with clear coat finish Liner – 29 gauge galvanized steel with primer 26 gauge galvanized steel on face and liner for fire rated walls Foam Insulation: Minimum 2.4 PCF polyisocyanurate foam

 

Peter J. Arsenault, FAIA, NCARB, LEED AP, practices, consults and writes about sustainable design and practice solutions nationwide. www.linkedin.com/in/pjaarch

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