The earliest seam joints were over-lapping flaps which were folded over and hammered flat to the roof, thus the term flat seam.
Later, as soldering techniques were developed, these seams were soldered to provide a sealed surface impervious to the weather.
While the growth of steel sheet goods grew in the mid-1800s, the invention of the “leaf- brake” allowed longer, straighter bends.
These bends were more accurate and could be formed much quicker than with hand tools. This made any metal roof style more affordable by pre-bending panels in a production environment using less skilled workers. Panels now 8-10 feet in length
became available. Installation was easier, saving money on installation costs and labor.
Common seams for these panels were of the standing seam type which kept the seam elevated and further away from the draining water.
Two world wars, production methods, and modern technology brought changes to manufacturing that would dramatically change metal roofing
Steel manufacturers found that they could take a very thin sheet of steel, and press lengthwise ridges into it by passing it beneath a “corrugating drum.” Modern roll forming equipment, as shown in Figure 2-8, adds ribs and ridges to flat material. These
ridges add strength to the panels. The panels could now span an open distance and did not require a solid deck surface beneath each panel. The panels now served as structural members as well as a roof surface. These corrugated panels now
made metal roofing a very economical choice in roofing. Metal corrugated roofs became “the roof of choice” in many applications.
Corrugated roofing was often installed using nails fastened to the “peak,” or “high point” of the corrugations. Later, fasteners with gaskets were developed. This allowed fasteners to be installed in the lower corrugations, or “valleys,” of the panel.
This same concept took a giant leap forward after World War II when roll-forming technology was developed. Instead of rolling sheets of metal, long coils were rolled and formed as a continuous process instead of one sheet at a time.
Roll Forming Equipment