Copper Wall Cladding: Modern Testing for Time-Proven Systems

Copper Wall Cladding:
Modern Testing for
Time-Proven Systems
Larry E. Peters
Copper Development Association, Inc.
7918 Jones Branch Dr., Ste. 200, McLean, VA, 22102
404-373-0324 • larry.peters@copperalliance.us
Frank V. Resso, PE
Resso Engineering, LLC
735 Cannon Rd., Sharpsburg, GA, 30277
678-357-3920 • frank@ressoengineering.com
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Larry Peters is the CDA’s project manager for the testing component of its Wall Cladding
Initiative. He has nearly 25 years of experience working with architectural metal wall cladding,
roofing, and flashing systems. Over 20 years of this experience has been dedicated to
copper systems. This includes technical assistance during initial design, as well as troubleshooting
and forensic analysis of installed systems. Peters also manages CDA’s Installation
Training Program and is thus skilled at hands-on techniques necessary to install traditional
copper cladding systems and related flashing.
Frank Resso has over 25 years of experience in engineering and design encompassing
virtually every segment of the building construction industry. He is a licensed engineer with
a special emphasis on the design, specification, product testing, and forensic investigation of
building enclosure systems, exterior wall cladding, and roofing systems. He recently participated
as a member of the ASCE 7-16 Wind Loads Subcommittee and various SPRI Canvas
Groups, and he was a longstanding member of the ASTM Committee E06 on Performance of
Buildings. Resso has presented numerous short courses on metal cladding, building enclosures,
and roof edge systems and is credited with nine U.S. patents on related systems.
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ABSTRACT
SPEAKERS
Copper—due to its inherent longevity, adaptability, and beautiful natural weathering characteristics—remains one
of the most proven and preferred roofing and flashing materials. With increasing adoption of light-gauge sheet metal
as wall cladding, today’s design professionals are again looking to copper to provide a high-performance option for key
buildings.
Until now, some specifiers were reluctant to specify copper; although time-proven, a lack of recognized system
testing for common traditionally formed copper wall systems proved a deterrent for some professionals.
The Copper Development Association (CDA) recently completed an exhaustive testing program encompassing
the battery of tests included within the American Architectural Manufacturers Association (AAMA) 509, Drained and
Ventilated Rain Screen standard.
Completed test protocols include:
• Air infiltration (ASTM E283)
• Water infiltration (ASTM E331)
• Wind resistance (ASTM E330)
• Dynamic wind (AAMA 501.1)
Tested Systems:
• Standing seam (double lock)
• Standing seam (single lock)
• Flat seam (long panel)
• Flat seam (diagonal orientation)
This presentation outlines tested systems, performance characteristics with sample wind resistance in different
regions, and availability of test results. It concludes by proposing system modification, should a building require even
higher performance.
INTRODUCTION
Once largely limited to sloped
roofing surfaces, light-gauge
sheet metals are now increasingly
used to cover vertical building
enclosure surfaces. In many
cases, such metal wall cladding
incorporates either identical or
very similar joinery as that used
for roofing.
Copper is an effective and
durable roofing and cladding
material. Many project examples
demonstrate decades and even
centuries of proven performance.
Although such copper systems
obviously pass the test of
time, modern design and construction
standards introduce
quantifiable performance criteria
demonstrated by mandatory
requirements in model building
codes. As a result, although
architects, engineers, and contractors
feel very comfortable with
performance characteristics of
traditional copper systems, they have pressure
to substantiate material selection in
accordance with recognized modern experimental
and analytical techniques.
Access to quantifiable technical data,
provided through recognized standardized
testing and analytical calculations,
provides assurance to design professionals,
cladding installers, inspectors, and
building owners, supporting material and
system selection. Understanding this need,
the Copper Development Association (CDA)
conducted a rigorous testing regimen and
now provides readily available performance
data for common copper wall cladding systems
in accordance with accepted nonproprietary
wall cladding test procedures.
SYSTEMS
Copper is recognized as one of mankind’s
oldest, if not the oldest, metal. It is
malleable enough to manufacture into thin
sheets and further form into more complicated
shapes without work hardening and
cracking, yet has enough strength to resist
loads. Impressive corrosion resistance provides
a protective surface coating, called
“patina” that, unlike rust, does not exfoliate.
The patina, for all practical purposes,
prevents aggressive atmospheric corrosion.
Since the patina—a distinctive light
grey/green tone in most wet climates, and
brown/black in arid regions—is considered
attractive, it effectively eliminates the
recurring cost necessary to paint many
other metals.
With such availability, formability,
durability, and relative economy, it is
understandable that builders historically
chose copper to protect key areas of important
buildings. For building enclosures,
copper was largely concentrated on sloped
surfaces, such as roofing and flashing; for
water transport (e.g., gutters and downspouts);
and ornamentation. Thus, copper’s
use as a roofing and flashing material
is long established. Many basic designs
of common systems proven and perfected
centuries ago are still used today.
In most cases, the vertical surfaces of
these historical buildings were masonry
(solid walls), with major exceptions, including
wood or stucco. All of these materials
served as the building’s outer skin. There
was little desire to use metal to cover such
surfaces.
But copper wall use did exist. These
builders normally did not differentiate
between sheet copper system use for
vertical vs. sloped surfaces. Hildesheim
Cathedral (Figure 1), in what we now know
as Germany, was long recognized as having
the oldest known copper roof in the world.
Cathedral records indicated portions of the
copper were laid in 1230 and performed
well until the cathedral’s destruction in an
air raid in March of 1945. Roof panel joinery
was largely identical to the same double-
lock and flat-seam joinery used today.
Close inspection reveals the cathedral’s
central cupola tower, added in 1367, is
clad with the same standing and flat-seam
system joinery as the roof areas. Thus,
we have over 650 years of experience with
some copper cladding systems still used
Copper Wall Cladding: Modern Testing
for Time-Proven Systems
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Figure 1 – Hildesheim Cathedral, Central Cupola. Photo Credit: Marc Veneman ©123rf.com.
today. Other historic properties reveal similar trends—the main roof of a monumental religious, government, or educational building is frequently copper—typically with proven standing-seam, batten-seam, or flat-seam joinery. Vertical copper cladding, however, was largely limited to portions of the sides of steeples, cupolas, and especially dormers.
Understanding this long history, the versatility of copper (if sheet metal cladding can be formed, it can be formed in copper) provides a testing dilemma: With limited testing resources, which systems should be prioritized?
After extensive review, the CDA decided to prioritize two of the most popular general types of copper wall cladding: standing seam and flat seam. Furthermore, within each broader category, we expanded into two options: for standing seam, we tested both double-lock standing-seam and single-lock standing-seam system varieties. And for flat seam, we included horizontal flat-seam and diagonal flat-seam systems (Table 1).
These four systems are common. They are proven. They are easy and economical to form. They are versatile; variations of essentially the same system are readily adaptable to different building shapes and many seam orientations.
Each system tested was fabricated from a common sheet thickness of readily available alloy and temper. We also decided to utilize pre-manufactured panel attachment cleats (clips) and fasteners (screws rather than nails) to establish a consistent panel attachment baseline.
Well-established practice considers system performance results applicable to identical seam configuration from either heavier-weight (thickness) sheet, narrower-width panels, or more frequent cleat/fastener placement. It is likely that thorough analysis or calculation will reveal greater performance from such system design and installation, if necessary, for specific projects.
STANDING-SEAM WALL CLADDING
In its most rudimentary form, a standing-seam system involves bending edges of a sheet of metal into a vertical leg, forming a panel, and then connecting legs of adjacent panels together (Figure 2). Concealed attachment cleats, attached to the underlying structure, are placed so that they are ultimately hidden within the finished seam. The standing seam resists loads, such as wind pressure or, more importantly, wind uplift, occurring perpendicular to the flat of the panel. Concealed cleats ensure there are no fastener penetrations, thus preventing potential leak points. The standing seams stiffen the panels, driving a component of thermal movement along the length of the seam. This movement is accommodated by a combination of cleat type selection and proper design at adjacent flashing or transverse seams.
Especially important for sloped roofing applications, the “opening” of each seam is above the plane of the building substrate. Thus, on roof panel seams, for leakage, there will need to be enough water buildup (ponding) to overcome seam height. For a wall, shedding water will need to overcome capillary attraction of the panel surface and somehow work itself through the tightly clinched seam. Ponding is unlikely, to say the least, on high-slope or vertical surfaces. Field observations on countless square footage of wall indicate it is unlikely for water to overwhelm standing seams on vertically oriented (wall) panels. (See Figure 3.)
Double-Lock Standing-Seam Panel
Double lock is the preferred standing-seam system for copper roofing and wall cladding. It is incredibly popular; the proven double-lock joinery is so functional and ubiquitous, it is often assumed the term “standing seam” equates to use of double-lock joinery.
Although virtually any seam height is possible, 1 in. is by far most common, followed by 1½ in. Conceivably, increased seam height may increase structural performance; it is unlikely higher seams will offer meaningful water infiltration resistance on vertical applications. Higher seams also use more material, and, at least with thin sheet metal, are more prone to damage.
Many cold working sheet metal fabrication techniques are possible to both form and seam the panels, ranging from hand tools, to stationary and portable sheet metal brakes, to roll-forming equipment. Regardless of the forming technique, characteristics of final seam engagement and ultimate performance appear to be identical. Hand-formed and -seamed panels seem to perform just as well as factory-manufactured and electrically seamed ones.
For this testing, panels were created on a commonly available portable sheet metal brake, then seamed during installation using common hand tools, such as wide-jaw seaming pliers, hammers, mallets, and seaming anvils.
Standing Seam Flat Seam
Double lock Single lock Horizontal Diagonal
Table 1 – Copper systems to evaluate.
Figure 2 – Standing-seam joinery.
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Twenty-six-gauge (26-ga) stainless steel expansion cleats, purchased off the shelf from a local manufacturer, connect wall panels to substrate. Per industry standard recommendations, expansion cleats are not required for panels that are 8 ft. long (the width of the test frame). We decided to utilize expansion cleats out of caution, however. Such cleats have a base piece, attached to the substrate, with an upper tab wrapped within the standing seams. The upper tab hooks through a slot within the base and engages the two pieces while allowing the top portion to move independently, accommodating a fair degree of thermal movement. This two-piece expansion cleat design, although proven very effective on countless roof and wall installations, is likely weaker compared to typical “fixed” cleats at ultimate wind loads. For one thing, the top portion of the sliding cleat is only roughly half the width of a typical fixed cleat. Post-test observations support this consideration.
Single-Lock Standing Seam
The single-lock standing-seam system is constructed somewhat like the double lock, with the following exceptions: The panel seam is only partially formed, leaving the final portion of the seam bent at 90 degrees from the vertical (Figure 2). A 26-ga stainless steel stiffener is installed within the vertical portion of the seam. Respected European sources, such as Kupfer Im Hofbau, by the Deutsches Kupfer-Institut, recommend such a stiffener to reduce potential for physical damage from point loads perpendicular to the seam side. Single-lock standing-seam wall cladding is often installed with seams running horizontally, likely increasing the chance of such stresses applied downward into the side of the seam. We considered it unlikely that the stiffener would affect wind resistance performance (later observed during testing).
Similar single-lock standing-seam profiles are very common as roofing, generally formed from 24-ga (or even 22-ga) steel.
North American copper references universally demonstrate a preference toward double-lock joinery. (Prior to this study, none showed single lock as recommended practice.)
FLAT-LOCK WALL CLADDING
Flat-lock systems (often called “flat seam”) are characterized by panels with very low-profile open-hem joinery on each side. Hems are typically ¾-in. deep (as tested) but occasionally formed wider or narrower for specific applications. Two adjacent sides of each sheet are folded over and two are folded under to form the ¾-in. locks. When installed, horizontal hem openings always face down the wall such that water always sheds over these seams and downward (Figure 4).
Concealed cleats affix each panel to the substrate. In many ways, flat-seam panels are a type of shingle, shedding water well only at higher slope. (A wall provides a great example of an extremely high-slope surface.)
The flat-lock wall systems should not be confused with flat-seam soldered (often called flat-locked and soldered), a system suitable only for very low-slope roofing.
Flat-lock systems are extremely popular for wall cladding. They are economical, as extra metal within each seam is minimized. They are versatile, with such low-profile
Figure 3 – Standing-seam wall cladding, Clearfork Campus, Ft. Worth, TX. 2016 North American Copper in Architecture Award winner, courtesy Cunningham Architects.
Figure 4 – Flat-lock joinery.
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seams easily adaptable to unique shapes. They are easily installed, reducing labor cost. Perhaps most importantly, flat-seam systems appear to work very well as wall cladding (Figure 5).
Panel size varies greatly. Although industry standard recommendations limit width to 24 in. (nominally, 23¼-in. actual exposure), some architects have specified panels at virtually full 3-ft. by 10-ft. sheet size. Oil canning is extreme on such very large panels, and we also expect ultimate wind uplift performance to be compromised. That said, we know of some large-panel flat-lock wall installations with over 20 years of proven performance.
Horizontal Flat-Lock Panels
Horizontal flat-lock panels are installed shingle style, bottom to top on a wall. Open-hem seams, ¾ in. wide, conceal attachment cleats that engage successive rows of panels. Although very long panels (formed from coil stock) are possible, they are usually a maximum of 10 ft. (current standard sheet length) and frequently, only 24 in. long. Standard practice staggers spacing of vertical transverse seams, easing installation while allowing any water driven to a transverse seam to shed and disperse on the next lower panel. Cleats are typically 2-in.-wide “fixed” design, from 26-ga stainless steel, with two fasteners per cleat. Thermal expansion and contraction is limited over such panel lengths; fixed cleats demonstrate such reliable performance that expansion cleats are virtually unknown for the system.
Diagonal Flat-Lock Panels
The diagonal flat-lock panel system is an interesting variation with the same ¾-in. open-hem joinery utilized in horizontal flat-lock panels. It is easy to install, yet provides a unique appearance, often described as “fish scale” or “diamond” pattern.
For testing, we decided to evaluate a common variation where each panel is formed from a square, with diagonal axis oriented vertically on the wall. The two seams on the bottom edge of each panel thus face toward the substrate, with the two edges at the top facing away from the structure.
Understanding that the mechanical seam engagement is identical to the horizontal flat-lock panel system, a major goal of the tests on the diagonal variant was to see how seam orientation and greatly increased length of seam per exposed square foot of panel (caused by relatively small panel coverage) would affect air/water infiltration while determining how decreased panel size (and associated increase in effective number of attachments per panel area) would affect wind uplift performance.
TEST STANDARDS
Exterior wall cladding materials, components, and systems are subject to a wide range of conditions, from climatic and environmental forces to human interaction and influence of the internal building state. Conditions affecting exterior cladding include wind forces, bulk water entry, humidity and water vapor transport, air infiltration and exfiltration, exposure to ultraviolet radiation, fire resistance, and impact from natural and human activities.
For the purpose of this research, scope of investigation and testing were limited to certain conditions affecting serviceability and structural integrity of each copper cladding system. Specifically, research focused on bulk water infiltration during severe storm events, air infiltration during drying periods with moderate climatic conditions, and resistance to negative wind pressure up to extreme failure situations. These conditions represent those most commonly associated with rainscreen wall design.
The rainscreen wall design principle was established in the 1960s as a modern interpretation of much earlier construction techniques. Over the past two decades, this effective design and construction technique has become very popular in North America. Essentially, the rainscreen wall design principle considers cladding to be an element of an exterior wall assembly that resists wind forces while limiting moisture ingress into the wall assembly and promoting drying of incidental moisture through drainage and ventilation of the wall cavity. Instead of attempting to establish a perfect seal between the exterior and interior environment, a rainscreen anticipates some amount of moisture within the wall assembly, with the goal of directing the moisture out of the wall assembly by means of cavity drainage and convective drying.
After a number of years of development, in 2009, the American Architectural Manufacturers Association (AAMA) published the AAMA 509 standard. As the most comprehensive and applicable standard for metal wall cladding systems, this standard was selected as the basis for testing of each copper wall cladding system detailed previously. This extensive protocol, entitled Voluntary Test and Classification Method for Drained and Back Ventilated Rain Screen Wall Cladding Systems, details a regimen of four well-established test methods for the purpose of creating a comparative classification system for exterior cladding systems. The AAMA 509 regimen includes:
Figure 5 – Horizontal flat-seam wall cladding, Gap Cove House, Rockport, MA. 2019 NACIA Award winner. Architect: Ruhl Studio Architects, Installer: Paul John & Son. Photo Credit: Paul Becker.
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• American Society for Testing and Materials (ASTM) E283: Standard Test Method for Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen
• ASTM E331: Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference
• AAMA 501.1: Standard Test Method for Water Penetration of Windows, Curtain Walls and Doors Using Dynamic Pressure
• ASTM E330: Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure
Note: ASTM E330, which tests strength of cladding under negative wind pressure, is a voluntary component of the AAMA 509 procedure; the remaining three test standards are mandatory for AAMA 509 compliance.
SPECIMEN PREPARATION
For the three air and water infiltration tests—ASTM E283, ASTM E331, and AAMA 501.1—a single test specimen was prepared and successively subjected to the procedures. The test specimen measured 8 by 8 ft. (2.4 by 2.4 m), with multiple vertical and horizontal panel joints. The head (top) and sill (bottom) edges of the test specimen were detailed and terminated in a manner typical of installed conditions, with appropriate flashing and trim components. The vertical side edges were considered continuous with adjacent sections of wall cladding. As such, they were terminated with simple flashings to maintain integrity of the specimen. Each copper cladding system included in this project scope was installed by means of premanufactured light-gauge stainless steel clips; the selected clips were from a popular and readily accessible nonproprietary supplier. Likewise, stainless steel fasteners were a common-style pancake-head metal-to-plywood screw procured from a nonproprietary supplier. Stainless steel clips and fasteners are commonly used with copper materials, as these metals are galvanically compatible.
Most copper wall cladding systems, as well as many other metal wall cladding systems, are installed on a solid surface of plywood sheathing. While other wall assembly configurations are possible, this is the most typical installation condition. This necessitates a specimen configuration such that the copper panels and clips are anchored into plywood, yet the plywood does not influence or impede the testing procedure or results. Narrow strips of 23/32-in. (18-mm) plywood approximately 3 in. (76 mm) wide along each line of panel clip locations simulated the sheathing. Strips were oriented vertically, horizontally, or diagonally, as appropriate for each copper cladding panel system.
A simulated “backup wall” completed the test specimen. The backup wall was formed from 2×6 vertical wood studs at 16 in. (406 mm) on center, inside a 2×12 wood test buck. A clear, rigid polycarbonate panel simulated the wall’s air barrier system and was located between the wood studs and the outer copper cladding system. In order to allow pressurization of the outer wall assembly (the space between the air barrier and copper cladding), the simulated air barrier was made “imperfect.” Numerous 1/8-in. (3-mm) holes were drilled through the polycarbonate until the airflow through the air barrier reached 0.12 cfm/ft2 (0.6 L/s•m2), which is four times the generally accepted rate for a properly functioning air barrier system. This rate of leakage was calibrated at a mild air pressurization level of 1.57 psf (75 Pa). In this manner, imperfections of field installation conditions were simulated in the laboratory environment. Finally, drainage channels were installed at various elevations at the inside and outside faces of the simulated air barrier. These channels were sloped and plumbed to collect any water that contacted the outer face of the air barrier or
Figure 6 – Double-lock standing-seam test specimen.
Exterior wall cladding materials,
components, and systems are subject
to a wide range of conditions, from
climatic and environmental forces
to human interaction and influence
of the internal building state.
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penetrated through to the inner face of the air barrier.
For the ASTM E330 structural wind pressure resistance test protocol, the test specimen differed in only a few details. A separate test specimen was constructed for each system, as the ASTM E330 protocol is a destructive test that may include structural failure. Steel studs, used in place of wood, limited deflections of the backup wall under load, and ensured safe achievement of higher test pressures. Most importantly, the rigid simulated air barrier was eliminated, and a thin, flexible plastic sheet was installed directly between the cladding panel clips and the plywood strip supports. This facilitated the test chamber applying the full and unimpeded air pressure acting outwardly, against the inside surface of the cladding panel. In this way, the specimen and apparatus simulated a negative wind pressure without any undue influence from supporting elements of the test specimen or apparatus.
The panel modules used to construct the double-lock standing seam test specimen (Figure 6) for air leakage and water infiltration were 20.75-in. by 96-in. (527-mm by 2,388-mm) panels formed from 16-oz. (0.0216-in. or 0.55-mm) thick H01 temper copper sheet, with 26-ga stainless steel anchor clips at 12 in. (305 mm) on center. For negative wind pressure capacity testing, the panels measured 15.25 by 96 in. (387 by 2,388 mm). Two #10 x 1-in stainless steel gimlet point pancake head screws were used to attach each panel clip to 23/32-in. plywood strips.
The same panels and construction as described above for double-lock standing seam specimens were used for the single-lock standing seam test specimens.
The panel modules used to construct the horizontal flat lock test specimen (Figure 8) for air leakage and water infiltration were 21.75- by 96-in. (527- by 2,388-mm) panels formed from 16-oz. (0.0216-in. or 0.55-mm) thick H01 temper copper sheet, with 26-ga stainless steel anchor clips at 12 in. (305 mm) on center. Each alternate course of panels utilized 48-in. (1,219-mm) long panels to provide a staggered vertical panel joint within the test specimen. For negative wind pressure capacity testing, the panels measured 15.75 by 96 in. (400 mm x 2,388 mm), alternating each course with 15.75- by 48-in. (400- x 1,219-mm) panels. Two #10 x 1-in. stainless steel gimlet point pancake head screws were used to attach each panel clip to 23/32-in. plywood strips.
The panel modules used to construct the diagonal flat-lock test specimen (Figure 9) for air leakage and water infiltration were 21.75- by 21.75-in. (527- by 527-mm) panels, as measured along the diagonal panel edges. The panels were formed from 16-oz- (0.0216-in.- or 0.55-mm-thick) H01 temper copper sheets, with four 26-gauge stainless steel anchor clips per panel. For negative wind pressure capacity testing, the panels measured 15.75 by 15.75 in. (400 by 400 mm). Two #10 x 1-in. stainless steel gimlet point pancake-head screws were used to attach each panel clip to 23/32-in. plywood strips.
AIR LEAKAGE PROCEDURE
AND TEST DATA
ASTM E283 determines air ventilation classification, as determined by AAMA 509. For this procedure, the test specimen is mounted to an air pressurization chamber (Figure 10), with copper cladding panels facing outward and vacuum pressure drawing air into the wall assembly.
Figure 7 – Single-lock standing-seam test specimen.
Figure 8 – Horizontal flat-lock test specimen.
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Each metal joint (including perimeter and flashing components) is sealed with tape. Once a calibration baseline air leakage measurement is recorded, individual joints are tested for air leakage. One at a time, the sealing tape is removed from each of four sheet metal joinery conditions—vertical panel joints, horizontal panel joints, head flashing, and sill flashing. Each joint is sequentially isolated, the air leakage at 1.57 psf (75 Pa) is recorded, and the joint is resealed with tape. Finally, a calculation is performed using the measured rates of leakage to compute the overall air leakage rate per unit area of wall surface. The results of the ASTM E283 air leakage procedure are given in Table 2.
WATER PENETRATION PROCEDURE AND TEST DATA
The water penetration classification for AAMA 509 is determined by averaging results of the ASTM E331 static pressure and AAMA 501.1 dynamic pressure water penetration procedures. Each procedure is performed at two test pressures: 6.24 psf (300 Pa), which represents a wind speed of approximately 50 mph (22.1 m/s), and 12.00 psf (575 Pa), which represents a wind speed of approximately 69 mph (30.8 m/s).
Each trial is conducted for a 15-minute duration with a water stream rate of 5 gal/hr/ft2 (1.76 L/hr/m2) directed at the outer surface of the copper wall cladding, while air pressure drives water inward into the wall assembly. Water that contacts or penetrates the simulated air barrier is collected and measured for each trial. Each of the four results —static and dynamic air pressure, at two test pressures each—is averaged to determine classification of the cladding system. Observations are reported indicating extent of water droplets that contact the simulated air barrier within the wall assembly.
The apparatus for the ASTM E331 static pressure procedure (Figure 11) is identical to the air pressurization vacuum chamber used in the ASTM E283 air leakage procedure. All sealing tape from the ASTM E283 test is removed from the specimen, and the
Figure 9 – Diagonal flat-lock test specimen.
Figure 10 – ASTM E283, Air Infiltration Test for Horizontal Flat-Lock System.
Cladding System Air Leakage, cfm/ft2 (L/s•m2) AAMA 509 Classification
Horizontal flat lock 7.64 (3.61) V1
Diagonal flat lock 0.11 (0.57) V1
Single-lock standing seam 7.78 (3.67) V1
Double-lock standing seam 0.12 (0.60) V1
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Table 2 – Air leakage results.
static pressure water penetration test is performed. For the AAMA 501.1 dynamic pressure water penetration test, the specimen is first mounted to a rigid steel test frame support. A turbo prop engine, with rpm calibrated to wind speed, is used to generate a turbulent airflow blowing inward against the cladding panels (Figure 12). The water source is injected into the airstream by numerous calibrated nozzles and driven at the outer surface of the test specimen. Again, water penetrating the cladding comes into contact with the simulated air barrier and is collected and measured.
The resulting average water penetration data from the ASTM E331 and AAMA 501.1 procedures and corresponding AAMA 509 classification is given in Table 3.
WIND RESISTANCE PROCEDURE AND TEST DATA
While the windward face of a building is subject to positive wind pressure, driving water into the cladding joint, the opposite side of the building—the leeward face—is affected by a different condition. Due to the building’s disruption of the air flow, the leeward face of the building experiences a negative wind pressure at the exterior face of the cladding, which acts to pull the cladding away from the wall structure. In most applications of metal cladding systems, resistance to negative wind pressure is the controlling design criteria. The American Society of Civil Engineers (ASCE) standard ASCE 7, Minimum Design Loads and Associated Criteria for Buildings and Other Structures, provides an analytical method for determining the
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Figure 11 – ASTM E331, Water Penetration Test on Double-Lock Standing-Seam System.
Cladding System Water Penetration, AAMA 509 Classification
oz/ft2 (ml/m2)
Horizontal flat lock 0.00 (1.17) W1
Diagonal flat lock 0.01 (3.55) W1
Single-lock standing seam 0.05 (15.19) W1
Double-lock standing seam 0.01 (2.09) W1
Table 3 – Water penetration results.
Figure 12 – AAMA 501.1, Wind-Driven Rain Test on Diagonal Flat-Lock System.
magnitude of wind pressure acting on a
structure. For walls, the standard indicates
negative wind pressure will be greatest
at leeward corners of the building and
increase with height above grade.
In order to produce a negative pressure
effect on the copper cladding system,
the ASTM E330 test specimen is inverted
on the vacuum pressure chamber, such
that the exterior face of the specimen is
mounted against the chamber (Figure 13).
As the air pressurization chamber draws a
vacuum, the negative pressure differential
pulls copper cladding panels away from the
wall assembly. The specimen is loaded in
successively higher increments until system
failure occurs. A minimum of five successful
load increments is required for a
valid test procedure. Each load increment
is sustained for a minimum of 30 seconds,
and elastic deflection measurements are
made at various locations of the specimen
while under load. After each successful
loading increment, the load is released,
and the specimen recovers. This recovery
period is limited to a maximum of five minutes.
Permanent set deformation measurements
are recorded when the specimen
reaches an equilibrium resting state.
System failure is recognized as loading
at which the cladding system no longer
sustains additional load or experiences
inelastic permanent deformation in excess
of accepted limits. Furthermore, elastic
deflection under load (a nonstructural
condition) is evaluated to ensure that the
cladding system functions unimpaired
and in a serviceable manner while loaded.
Generally, the failure of metal cladding
systems under negative pressure loading
is a sudden and acute failure wherein the
panel joinery becomes disengaged and permanently
buckled. Other common failure
modes include disengagement or internal
failure of clip anchors and fracture or pullout
of fasteners. The results for each copper
cladding system are given in Table 4.
ANALYSIS OF RESULTS
The goal of rainscreen wall cladding
testing is to determine a system’s classification
for watertightness and air ventilation
potential. By classifying such systems,
designers, installers, and end-users are
better able to compare the relative performance
potential of various cladding systems.
AAMA 509 results are expressed in a
water infiltration classification of W1 (least
water penetration) to W11 (most water
penetration), and an air ventilation classification
of V1 (least air flow) to V11 (most
air flow).
The water infiltration rate and classification
are obvious and intuitive: the less
bulk water that penetrates the cladding,
the lower the volume of moisture in the
wall assembly to be mitigated. Air leakage
performance, on the other hand, is
less intuitive. Lower air infiltration rates
are desirable for traditional, face-sealed
cladding, indicating a near-airtight barrier
between the outside environment and
the interior of the wall assembly. However,
higher rates of air infiltration are desirable
for rainscreen cladding systems, as
they promote greater potential for drying
through convective air flow within the
wall cavity. While there is no authoritative
benchmark for an acceptable ventilation
classification of a rainscreen cladding system,
it may be generally deemed to be “in
balance” when the ventilation classification
equals or exceeds the water penetration
classification.
As the prior tabulated results indicate,
each copper wall cladding system evaluated
achieved an AAMA 509 classification
of W1/V1. While convective drying potential
is somewhat limited as indicated by the
V1 classification, the W1 water infiltration
classification signifies that these labyrinth
joinery, traditional-style copper wall cladding
systems are virtually watertight on
vertical wall planes—all without the use of
seam sealants or other gasketing materials.
We expect that the ventilation rating could
IIBEC 2020 Virtual International Conve ntion & Trade Show | June 12-14, 2020 Peters and Ress o | 163
Figure 13 – ASTM E330, Wind Resistance Test on Single-Lock Standing-Seam
System.
Cladding System Wind Pressure at Failure, psf (Pa)
Horizontal flat lock 85.20 (4,080)
Diagonal flat lock1 208.00 (9,960)
Single-lock standing seam 80.00 (3,830)
Double-lock standing seam 127.70 (6,115)
1. No failure occurred in the diagonal flat-lock specimen; the blower apparatus reached its maximum
capacity to load the specimen.
Table 4 – Wind Resistance Results
be further enhanced by selecting or developing head and sill flashings that provide additional free air flow. The overall conclusion from these accumulated test results indicates that these traditionally joined copper cladding panel systems can be expected to provide excellent performance when incorporated into a properly designed and installed rainscreen wall assembly.
The negative wind pressure resistance of the four copper cladding systems varied in ultimate magnitude of load before system failure, with one system demonstrating a capacity greater than the maximum load that could be exerted by the testing chamber. However, even the system with the lowest load at failure exhibits a capacity sufficient for use on multistory buildings in all but the very highest wind region in North America. In recognition of the extensive and sustained historical use of copper cladding systems, the outstanding results (Table 5) are not entirely unexpected.
Generally, there is some correlation between clip density (and more frequent crosswise restraint) and wind resistance. The diagonal flat-lock specimen has significantly higher overall clip density and performs on an order of double the strength of the other systems. It is also apparent that for standing-seam systems, a double lock is superior to a single lock for both strength and weathertightness performance. With the seam crimping technique being virtually the only variable between the two standing seam test specimens, the double lock achieves a 50% higher wind resistance failure load, and exhibits on the order of seven times less air leakage and water infiltration (although both systems can be shown to perform adequately for a wide range of design applications). In summation, the ASTM E330 testing on these four traditional copper wall cladding systems validates their consideration as a robust cladding choice for even extreme wind conditions.
With double-lock standing seam, observations and analysis demonstrate that as the system approaches ultimate wind failure, panels tend to invert simultaneously with expansion clip failure (top portion of clip twisting, with similar twisting at the base slot). Increased performance of the system could likely be achieved by increasing copper thickness (i.e., a move to 20 oz.). For such thicker panel material, a corresponding change to the expansion clip mechanism is recommended. To deter this twist, increase the gauge of the clip (perhaps 24 vs. 26 ga), or use fixed cleats (for appropriate panel lengths, which tend to be common in wall systems).
Single-lock standing seam achieves useable performance results, but wind uplift resistance is (as predicted) significantly lower than with double lock. North American copper industry guidance and the preference toward double lock appears universally accepted. It is doubtful that any small reduction in labor to avoid fully double-locking each seam is worth the resulting reduction in wind resistance. Indeed, the increased cost of additional optional stiffeners, combined with increased labor of stiffener installation, likely far outweighs any perceived “seaming” savings.
Flat-seam systems appear to function well. Understanding the extreme wind uplift resistance of the diagonal flat-seam system, additional research on the horizontal flat-lock panels is warranted. With a commonly utilized 18- by 24-in. dimension, horizontal flat-lock performance should prove very interesting, and better fill the large void in wind performance data between the rather long horizontal panels and smaller diagonal panels tested.
In no case did we experience a fastener failure. Common industry practice is to use two fasteners, in part to accommodate variances in substrate. Generally, prudent design practice attempts to avoid failures involving connections and fasteners in order to develop the full strength capacity of metal panels.
164 | Peters and RessESSo IIBEC 2020 Virtual International ConveVEntion & Trade Show | June 12-14, 2020
As this laboratory
testing and extensive
field experience supports, copper cladding systems should be one of the
systems considered when specifying and designing
high-performance exterior
wall assemblies.
Wind Velocity 145 mph 135 mph 120 mph 108 mph 95 mph
(65 m/
s) (60 m/s) (54 ms) (48 m/s) (42 m/s)
Example Locations Tampa Orlando Manhattan Pittsburgh Seattle
Charleston Houston Atlantic City Charlotte Portland
Galveston Norfolk Raleigh Atlanta Los Angeles
Austin
Single-lock standing seam 60 (18) 60 (18) 116 (35) 246 (75) 597 (182)
Horizontal flat lock 60 (18) 64 (19) 145 (44) 302 (92) 742 (226)
Double-lock standing seam 158 (48) 261 (79) 596 (181) 1,200 (366) 1,200 (366)
Diagonal flat lock 876 (267) 1,200 (366) 1,200 (366) 1,200 (366) 1,200 (366)
Table 5 – Maximum allowable height for above grade systems as tested,1,2 in feet (meters).
1. Based on ASCE 7-16 LRFD method for Components and Cladding Wall Zone 5 of buildings with Risk Category II and Exposure Category B.
2. This table is provided for illustrative purposes only. A qualified design professional must evaluate specific projects and applications.
FURTHER RESEARCH
AND CONCLUSIONS
While the test results were very impressive, we did note a few areas where further research might both prove interesting and result in even higher performance:
1. Evaluation of other design conditions, such as fire performance and impact resistance
2. Testing to include generic, and occasionally used wall systems such as “cassette” or traditional batten-seam system variants
3. Determining the extent to which thicker copper sheet material improves system performance
4. Conducting additional testing on smaller panel modules, including narrow widths, and shorter panels with additional crosswise restraint
5. Investigating the effect, if any, of taller (i.e., 1.5-in.) seams on standing-seam systems
6. Investigating additional head and sill termination techniques to provide additional ventilation and drying capacity of the wall cavity
Overall, the results are consistent in all areas of performance and similar to expectations based on considerable experience observing field and laboratory performance of copper and other metal wall panels formed in similar fashion. Indeed, such systems have performed and continue to perform well when installed properly to industry standard recommendations.
Prior field observations identify poor installation as an obvious exception to expected performance. Some such installation deficiencies include an increase in fastener spacing under misguided attempts at economy, deterioration of substrate material (generally on extremely old installations), and exposure to extreme damage, such as where the entire building enclosure is compromised. As this laboratory testing and extensive field experience supports, copper cladding systems should be one of the systems considered when specifying and designing high-performance exterior wall assemblies.
REFERENCES
Architectural Sheet Metal Manual (SMACNA Manual) (www.smacna.org). Sheet Metal and Air Conditioning Contractors’ National Association, Inc.
Copper in Architecture Handbook (A4050). (Available for free download at copper.org.)
Copper and Common Sense. Revere Copper. www.reverecopper.com.
Kupfer Im Hochbau, c. 1999. Deutsches Kupfe-Institut e.V. alle Retch. Auch die der Ubersetzung, vorbehalten.
Modern Applications of Sheet Copper in Building Construction. Copper & Brass Research Association, John Gowen, ed. Wealth of information on sheet copper roofing, flashing, and gutters. Indirect predecessor to Copper in Architecture Handbook. Out of print. 1955.
Rain Screen Wall Cladding Systems Testing. Architectural Testing, Inc., now Intertek. January 2010. Background on the history and development of the AAMA 508 and 509 testing standards.
The Rain Screen Principle and Pressure-Equalized Wall Design. American Architectural Manufacturers Association publication CW-RS-1-04. Revised November 2004. Historical background, mechanics, and design recommendations for rainscreen wall cladding.
F. Resso. “Performance Standards for Metal Rainscreen Wall Systems.” Metal Construction News. November 2014. A brief article detailing the procedures and use of the AAMA 508 and 509 test standards.
Standards/American Architectural Manufacturer’s Association
AAMA 501.1-05: Standard Test Method for Water Penetration of Windows, Curtain Walls and Doors Using Dynamic Pressure
AAMA 509: Voluntary Test and Classification Method for Drained and Back Ventilated Rain Screen Wall Cladding Systems
American Society of
Civil Engineers
ASCE 7-16: Minimum Design Loads and Associated Criteria for Buildings and Other Structures.
American Society for Testing
and Materials
ASTM E283-04(2012): Standard Test Method for Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen
ASTM E330-14: Standard Test Method for Structural Performance of Exterior Windows, Doors, Skylights and Curtain Walls by Uniform Static Air Pressure
ASTM E331-00(2016): Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference
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