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Metal Roofing from A (Aluminum) to Z (Zinc) - Part V



   Author: MetalMag


The original shapes of metal panel profiles were quite simplistic as were the tools used in their making. Smiths hammered out small plates of brass, copper or gold more than 2,000 years ago. They were then folded at their edges and interlocked one-tothe-next to form the “flat-locked” or “flat seam” style roof. The anchorage was accomplished with a small cleat folded into the joint area during installation. This style is believed to be the original metal roof type, and is still popular today, especially for irregular shapes like domes and onion domes. With the advent of soldering in the mid-to-late 1800s, these roofs could be used dead flat with soldered “hydrostatic” joints.

At some point, more than 1,000 years ago, craftsmen learned that they could fold the adjacent edges of a flat plate up at 90°, and then fold the top of the upstanding edges together into a tightly formed 360°, creating a double folded lock. This all resulted with the joint being raised above the drainage plane of the plate an inch or so, hence it was more water resistant. The joint was now standing up in a vertical orientation, rather than laying flat—hence “standing seam” was an appropriate designation to differentiate from the earlier “flat seam.” Once again, the anchorage was accomplished via a small cleat nailed to the structure and folded into the seam.

When the craft migrated from the Middle East to Europe during the Crusades, metal roofing profiles were adapted to the styles of architecture and climate prevalent in Western Europe and Scandinavia. Steep roof areas and “tiered” architecture (roofs above lower roofs) would dump snow and ice, damaging fragile standing seams below. A strip of wood inserted between the upstands of adjacent plates would support the seam area increasing the durability of standing seams, and creating a new style—the “batten seam,” so called because of the wooden batten strip.

A significant nuance was the introduction of a separate joining component—the batten cover that locks into two twin upstands and completes the joint. This was a departure from the other profiles that used a “male” and “female” seam edge, which were then interlocked with each other. A modification of the batten seam is the “batten roll.” This profile uses a raised “lap seam” (no separate batten cover) and was developed with and for lead roofing to provide more gentle radii for this unique material.

All these styles were fabricated at the point of installation, and with very simplistic tools—mallets, malletting anvils, tongs, hand and foot brakes, and later, simple pan formers. The metals used were soft, malleable materials, and could be meticulously formed, folded and jointed using these tools, shapes and techniques. And so was the craft of metal roofing for centuries of time. It was relatively unchanged until the industrial revolution. A metal roof was the finest and most expensive roof that could be had.

The effects of changing fabrication equipment
With the improvements in mining and milling techniques, as well as innovation in fabrication tools and equipment, new styles of metal roofing began to emerge. New materials were coming onto the scene as well. The steel industry was making huge strides into the commercialization of sheet goods in the early and mid-1800s, and the harder, less expensive material could be fabricated in a new fangled thing called a “leafbrake.” This device had a long jaw, and a hinged apron that could clamp the material and fold a perfect, straight bend far more quickly and accurately than the old (and much shorter) hand and foot brakes. This new equipment made any metal roof style more affordable, saving much time by “pre-bending” standing and batten seam profiles in a production environment by less-skilled workers.

Corrugating
Another interesting development around the turn of the century was a process called “corrugating.” Steel producers found that they could take a very thin sheet of galvanized steel, and press lengthwise wrinkles into it by passing it beneath a “corrugating drum.” The wrinkles stiffened the sheet such that the metal could now span over open supporting structural members without benefit of a continuous deck. Thus a “structural” covering would fulfill the function of both deck and roof membrane with one material.

The corrugating of steel panels was the first real mass-manufacturing process for metal cladding, and the resulting products made metal an economical roof material for the first time in history. Whereas metal had always been the most expensive roof that could be bought; now it was also the least expensive.

This corrugated metal was attached with exposed fasteners. It was, in other words, “face-fastened” or “through-fastened,” meaning that the weathering surface was pierced with nails (and later screws) to secure the product in place. Early applications located the nails in the “high corrugations,” but later weather-sealing washered screws came into use as well. Side-seams were joined in overlapping style, as with the earlier “batten roll” methods of roofing.

Roll forming
Innovation continued throughout the next half century, and the leaf brake helped birth a few new profiles—including the integrated batten seam, the button punched standing seam, and another structural panel—the “trapezoidal rib.” But the most significant advancement in manufacturing did not come along until World War II when “roll forming” technology was invented. This approach to making a profiled sheet was the first departure from a one-at-a-time manufacturing mentality. The progressive roll tooling of such a mill could produce a finished profile in a continuous process rather than step-by-step bending, or sheet corrugating one-by-one.

Another benefit attributable to this new manufacturing method was the precision with which panels could be formed. One end of the panel would be dimensionally consistent with the other—within thousandths of an inch! This had never been possible with leaf braking. The roll-forming process also opened the spectrum of available metal panel profiles, allowing intricate shapes, lines and bends never before possible or affordable. This equipment today can operate at line speeds of up to 600 feet per minute, automatically measuring and cutting panels to length with amazing accuracy at the same time.

The concept of continuous manufacturing—dealing with an endless strip of material—now pervades almost every aspect of production and fabrication including painting, profiling, curving, seam closing, slitting, leveling, and even sealant injection. The roll forming process has found its way from large in-plant mills to smaller, portable “onsite forming” machines as well as electric seam-folding machines. Whenever long, parallel bend lines are found on metal panels, it is a reasonable bet that the profile was made by roll forming.

Sometimes press-forming is used in tandem with roll forming to produce still different effects like some of the popular tile facsimiles available in the marketplace, or for “crimp curving” or to break a profiled (roll-formed) sheet over the ridge area. Press forming is also used for the manufacturing of individual shingles or tiles, and other textured shapes that are not characterized by long panels with parallel bend lines.

Of course roll forming technology has made a whole host of new profiles possible, and the manufacturing of the old ones much more cost effective. Another new concept to come along in panel profiling within the last few decades was the creation of snap-together seams and snap-on caps. This method uses the spring action of harder and higher-yield metals along with the dimensional consistency of modern roll forming equipment to develop locks and joints that do not require field folding or crimping.

Profiles and joints for “structural” panels
The use of standing seam joints and profiles on structural steel and aluminum panels is a trend that started with Armco Steel pre-1950. The concept was boosted with Kaiser’s introduction of a product called “Zip Rib” in the 1960s. This was a “bulb seam” design held in place with concealed clips, and it was popularized worldwide. Then about 1970 Butler Manufacturing introduced MR24 in the United States, the first standing seam joint used in conjunction with a trapezoidal rib panel profile. It was a curious blend of old and new. A 1,000-year-old joint on a relatively new material and profile—then used atop pre-engineered metal buildings. This revolutionized the metal building industry and since then, every major U.S. manufacturer of pre-engineered steel buildings now offers a structural standing seam alternative.

There seems to have emerged from within the metal building industry two panel geometries: the flat pan and the trapezoidal rib. There have also emerged two different types of joints: male-female interlock, and applied cap. With applied cap profiles, the cap is the female component of the assembly, and the panel edges are mirrored male components. Additionally, either of these joint types (interlock or applied cap) may be snapped together or mechanically crimped or folded. It seems that recent trends are more toward mechanically folded seams, probably because they are generally more durable with respect to wind resistance. Clearly, snap-together type seams are less labor intensive to install. For that reason they will always remain popular.

Which is best?
There is no clear answer to the question “Which seam and profile is the best?” Everyone has biases and there are pros and cons of any profile and seam type. My personal favorites are generally profiles that involve no void area within the seam.

Profiles that have void areas within the seam are cumbersome shapes to deal with at panel termination points—especially when those points are skewed, like at hips or valleys. But on the other hand, if the job does not involve such conditions, the trapezoidal profile (having the largest void area of any shape) may offer cost efficiencies not enjoyed by other profiles as it is a very material-efficient shape.

All things considered, it is hard to beat the original double folded standing seam. It has been around for more than 1,000 years, and is sure to be around for a very long time still to come.

New technology brings new challenges
Prior to the advent of roll forming, panel lengths were generally limited to 8 or 10 feet—the length of a traditional leaf brake. With the roll-forming process, panel lengths grew longer and longer, not being limited by fabrication equipment, but only by transportation restrictions. This makes sense, since longer panel lengths mean fewer end-to-end joints that are expensive to execute and can be problematic.

As the panel lengths increased, however, we also began to experience roof failures associated with thermal effects. With increasing panel lengths, panel attachment methods had to gain sophistication in order to accommodate the increased effects of thermal cycling.

In the next segment, we will look at dealing with thermal cycling characteristics of metal panel systems.

Rob Haddock is president of the Metal Roof Advisory Group, Ltd., and a well-recognized authority on metal roofing. He is a consultant, technical writer, training curriculum author, inventor and educator. He is a member of NRCA, ASTM, SBA, and MCA as well as a course author and faculty member of the RIEI.


Comments: Metal Roofing from A (Aluminum) to Z (Zinc) - Part V

I have a hangar, 80' x 100' and need to replace damaged panels. They are 38" wide and 12' and longer. There are many shapes and I first need to identify them. Can you help?
By James Hill
Post a comment > -


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