Metal cladding. Insulated metal panels (IMPs) and metal skin cladding, along with composite metal panels, are considered a cost- effective way to clad exterior walls, with a variety of colors, textures, and styles available. For example, corrugated metal panels are a common choice for Building Teams seeking a high-tech look—a sharp departure from their former agricultural and industrial connotations.
Thomas Chinnock, AIA, an Architect in the Phoenix office of Shepley Bulfinch (www.shepleybulfinch.com), agrees that metal cladding panel aesthetics are usually appealing. This is particularly true in situations where the manufacturer shapes the panels to request, and the specifiers can choose their own joinings and trim. “However, when a pre-established system is used, we are subject to manufacturers’ standard trim and joints, which tend to be larger than necessary because of their self-assigned tolerances,” says Chinnock.
IMPs and other metal façade assemblies are also known for their relatively light weight, which makes them cheaper to transport and easier to erect. It’s fairly simple to support metal panels off a substructure and barrier wall to allow for an ample cavity with plenty of continuous insulation, says David Altenhofen, AIA, a Building Enclosure Consultant and Manager with The Façade Group (http:// facadegroup.com). Another benefit is longevity, adds George M. Blackburn III, AIA, NCARB, General Manager of Construction Consulting International (www.sunited.com). He cites the stainless steel panels atop of New York City’s Chrysler Building as proof of the long-term stability and successful application of metal cladding.
Blackburn warns that material selection is critical. “I have seen corrosion of some steel alloys, where the panels have completely rusted through in a relatively short time,” he says, mentioning “weathered steel” products meant to form a rustlike finish that eliminates the need for coatings or finishes.
Generally speaking, however, metal is quite durable, though performance depends on proper detailing. For example, Chinnock says Building Teams should not rely on joint sealants for long-term weather resistance.
“Any system with sealant joints adds the risk of the sealant at- tracting atmospheric dirt and then staining the panels during a rain,” agrees Altenhofen, who helped found the AIA Philadelphia’s chapter of the Building Enclosure Council and is co-chair of the BEC’s National Research Committee, as well as sitting on the National Institute of Building Science’s Building Energy and Thermal Envelope Council (BETEC). Blackburn—a member of the BEC-Dallas Chapter as well as BEC’s National Research Committee and the BETEC Board of Directors—advises specifiers not to use metal panels in face-sealed wall designs in which all joints require sealant to prevent water penetration.
While the metal panels themselves are frequently airtight and watertight, their joints are not, and so the cladding systems require proper air barriers, says Richard Keleher, AIA, CSI, LEED AP, a Senior Architect with Thompson & Lichtner (http://thompsonlichtner.com). He advises Building Teams to carefully review claims made by panel producers about the air and water tightness of a complete system, since air barriers may not be a part of a given manufacturer’s product. A related issue has been the prevalence of poorly installed air barriers for metal cladding systems; in fact, several major suppliers of metal composite panels recently teamed up with the American Architectural Manufacturers Association and Architectural Testing to develop two tests to properly evaluate open jointed systems. The resulting standards are AAMA 508 for pressure-equalized rainscreen systems and AAMA 509 for back-ventilated and drained rainscreens.
“The objective is to have the least water penetration and the most ventilation,” explains Keleher, who also sits on BETEC’s Board of Directors and co-chairs AIA Boston’s BEC Chapter, which he helped found. “AAMA 509 provides performance on two scales—water penetration and ventilation—with a numerical range in each category from one to 11.”
Exterior insulation and finish systems. Transcending first- generation products from the late 1960s, today’s exterior insulation and finish system assemblies can provide a cost-effective, high-performance solution, according to William R. Brody, VP with the construction management firm B.R. Fries & Associates (www.brfries. com). “When detailed properly, EIFS offer a plethora of advantages,” says Brody. “The thermal value is very good, and the entire system is usually outboard of the structure, providing continuous insulation that reduces energy losses caused by thermal bridging.”
In addition, says Shepley Bulfinch’s Chinnock, a continuous building wrap can easily be achieved with an EIFS. Characteristics that control water infiltration include direct shedding off the surface, drainage
channels within the system, and a water-resistant membrane against the sheathing. “The water, in all cases, is directed away from the building with flashing and weep screeds,” says Chinnock.
The Façade Group’s Altenhofen emphasizes the need for meticulous design with EIFS. “Edges, openings, and penetrations have to be very carefully detailed for durable performance. Without paying attention to every detail, even down to mounting a light or sign, there can be very quick localized failure of the wall.” When carefully detailed, he adds, “In our experience, EIFS seldom have problems.”
While EIFS are generally quite serviceable when installed as drainage-plane assemblies, many Building Teams prefer the level of performance offered by back-ventilated, drained-cavity (BVDC) types of EIFS walls or rainscreen assemblies.
EIFS products come in many colors and finishes, including smooth, patterned, and textured options. A typical EIFS exterior may require repainting or refinishing every five to 10 years, and it may be a challenge to match the color and finish for repair work. The category also continues to battle notions that EIFS constitute a “cheap” finished building product, says Chinnock, mainly due to poor design and installation in some low-quality buildings.
Stucco. In general, stucco is durable, cost-effective, and aesthetically versatile for a range of building types. As a simplified weather barrier system, a stucco wall must be able to shed all elements, as there is little opportunity for ventilating and drying out, according to Chinnock. The joints must be mechanical—such as reglets or flash- ing—and expansion joints are specified at regular intervals, typically every 144 sf or 12 feet on center and at all floor lines. “This can be limiting to the aesthetics of the wall design,” Chinnock adds.
“All of the control joints required for stucco are disturbing for some architects,” agrees Altenhofen. “And developing details for continuous insulation with stucco are more difficult.”
As with EIFS, it can be difficult to match stucco colors and finishes during repair jobs. Typical wall specifications call for refinishing every five to seven years. There may also be performance considerations, says Construction Consulting International’s Blackburn. For instance, unexpected cracking can occur in stucco installed on metal-stud- framed walls. “We regularly investigate stucco defects of this type,” Blackburn adds. Hairline cracks rarely present a cause for concern, however, and they are typically not a warranty defect (depending on how the air and water barriers are installed behind the stucco).
Brick and masonry. Very common cladding materials, brick veneer and masonry veneer deliver durability at a reasonable cost, although maintenance is required over time. Historically used in solid, multiple-wythe walls, brick and masonry have evolved into a plethora of sophisticated systems combining veneer walls with drainage cavities attached to interior structural concrete masonry unit (CMU) structures or metal stud-frame assemblies, or a combination of the two.
Blackburn stresses the importance of installing air and water barriers on the interior wall system’s exterior face, with flashing and adequate weeps to drain water to the outside. Done correctly, the resulting brick and stone cladding systems are capable of delivering a long serviceable life, with some lasting for many decades. At the same time, the longevity and durability of thin-stone wall claddings are very much dependent on the performance of the mechanical supports and anchors. “We have investigated walls where the anchors were failing or the attachments into the stone caused the stone to fracture,” Blackburn says.
Terra cotta. Also offering long life and durability, terra cotta lends a unique palette of smooth textures and ruddy or brownish-orange colors as a cladding material. Engineered terra cotta façade systems generally work well and provide good protection against the elements. “Terra cotta is currently a popular treatment because it is an attractive, aesthetically pleasing product,” says A.J. Giglio, a Project Envelope Specialist with Gilbane Building Company. “W have done many successful installation of terra cotta, including k-12 schools and universities. It requires planning, as it can be more labor-intensive to lay out“
The façade Groups Altenhofen points out that many cladding systems involving terra cotta are marketed with complete open joints and incorrectly labeled as “rainscreens.“ “I believe the term rain screen gives some false sense of heightened performance, since rain screen assemblies, when properly detailed, should stop nearly all water penetration at the line of the cladding. Open-grille-type cladding layers do not stop enough water penetration, so there may be a great deal more water at the air barrier and water-resistive barrier layer” The result is greater risk of water leaking into the building. Such assemblies should really be categorized as barrier walls rather than high-performing rainscreens, in Altenhofens opinion.
Some façade consultants don’t recommend open-grille system for anything higher than three stories. In addition, the panels move quite a bit with thermal cycling, so attachment details must be carefully designed to accommodate the full range of expected movement.
Fiber-cement panels. Breaking away from its niche as siding material, fiber cement panel (FCP) claddings are increasingly being used as rainscreen system, similar to terra cotta and high-pressure laminate (HPL) panels. “The new uses of FCP product apppear to be durable,” says Blacbum, “but the method of attachment and support is critical to the longevity.” As a rainscreen system, the FCP materials are usually installed on wood battens or metal hat channels over a weather barrier, which then goes over the sheating. “It is ideal to have the insulation over the sheathing to create a continuous thermal barrier, but there must be sufficient space between the insulation and FCP to allow ventilation,” says Chinnock.
One drawback, according to Chinnock, is that flashing must be installed at every floor line - potentially detracting from the aesthetics of the panel layout. The panels can be difficult to repairs well. The pre-finished pieces are hard to touch up, and a cracked or chipped panel can be difficult to replace.
Beyond rainscreens, FCP can be used as a standard reglet trim system, custom trim pieces, or open joints. If installing an open-joint design, Chinnock recommends UV tape for the water-resistant barrier behind the joints.
High-pressure laminate panels. HPL. Panels - though mainly manufactured in Europe - are increasingly showing up in American rain screen applications. Air and water barriers are installed on the supporting wall behind. As with FCP, performance depends on the method of attachment, as well as proper installation of air barriers and water barriers.
There’s another similarity to FCP, says Thompson. & Lichtner’s Keleher: Since there is no visual and ultraviolet baffle at the open joints, a dark-colored drainage plane sheet is necessary over the insulation in the drainage cavity behind the cladding. “This is to prevent the insulation from showing and, for mineral wool insulation, to keep the insulation from getting wet,” he say. “It is critical that this drainage plane be vapor-permeable, to allow the insulation to dry out if it does get wet.”
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