The historic Justin Morrill Homestead, the Gothic Revival-style home of U.S. Sen. Justin Smith Morrill in Strafford, Vt., has pressed metal roof shingles. Photo by Adrienne Dickerson.

Beauty and function: Pressed metal shingles were an innovative 19th-century building material

This story appeared in the May issue of PRC’s Preservation in Print magazine. Interested in getting more preservation stories like this delivered to your door nine times a year? Become a member of the PRC for a subscription!

by Adrienne Dickerson, Architectural Historian

During the 19th century, the growth of urban areas and the expansion of settlement in America spurred a need for new, innovative building materials. These materials needed to be compact, lightweight and easy to transport to distant locations. Safety concerns required the products be both durable and fireproof, and the economy of the time required materials that could be manufactured quickly and affordably. In the mid-19th century, the development of the pressed metal shingle met all of these needs.

Rolled sheet metal had been used as roofing since the late 18th century. The development of metal shingles, though, broadened the scope of use as exterior cladding while adding aesthetic appeal. Metal shingles provided the rhythmic pattern of wood, slate and clay shingles, only with increased durability and lighter weight.

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Originally manufactured primarily as roofing, they were constructed from a variety of materials, such as lead, galvanized iron, tin, copper and terne plate, a thin steel sheet coated with an alloy of lead and tin.

Copper proved to be very expensive, and lead was weak and subject to creep caused by fatigue as a result of temperature-induced expansion and contraction. That being said, tin and galvanized iron shingles provided a happy medium between affordability and durability.

Pressed metal shingles were manufactured from rolled sheet metal molded into various decorative designs ranging from Spanish shingles, shaped to mimic rounded ceramic tiles, to decorative fish scale and Victorian shingles. This process called stamping was generally performed using drop hammer presses, which used hydraulic power to press the sheet metal into patterns in a swift, forceful motion. There are several companies in operation that still utilize original machinery and press plates from the late 19th century to produce historically accurate reproductions of original pressed metal shingles for restoration and new construction.

Patterns pressed into the metal shingles were designed not only for aesthetics, but also with movement of water in mind. The designs provide systems of ridges and channels allowing for downward flow of water with minimal obstructions.

Image 1: This image from a 1911 catalog from Pedlar People Limited, a sheet metal stamping company, shows a balloon-frame house being clad in its metal shingle siding and roofing.   Image 2: The historic Justin Morrill Homestead, the Gothic Revival-style home of U.S. Sen. Justin Smith Morrill in Strafford, Vt., has pressed metal roof shingles. Photo by Adrienne Dickerson.

 

Part of the ingenious design of metal shingles was the minimal overlap needed during installation because of their interlocking systems. Conventional wood or slate tiles required a large overlap area to prevent water intrusion while metal shingles relied on systems in which shingles were interlocking with small overlap.

As innovative as pressed metal shingles were, their use was not suitable for all architectural styles. While they met the need for affordable fireproof cladding that was easy to manufacture and ship, they simply weren’t as effective at shedding water as traditional materials. In fact, metal shingles were also used as siding on wooden framed commercial buildings as early fireproof cladding but were quickly phased out by large metal panels pressed to look like brick, clapboard or stone walls that had minimal connections, thereby reducing the potential for moisture intrusion.

Because metal shingles were less effective at shedding water, steeper pitched roofs were required. Architectural styles influenced roof pitch and cladding materials, so pressed metal shingles were primarily used on houses designed with high, steep rooflines, such as Gothic Revival and Queen Anne style buildings.

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While steep rooflines are prevalent in northern states where snow and ice buildup are a common issue, roofs of the Gulf Coast states that are prone to hurricanes and tornadoes are generally lower in pitch to accommodate for high winds. As the pitch of rooflines decreased, so did the efficiency of metal shingles at shedding water. This ongoing problem led to several iterations of new and improved locking systems, developed between the mid- to late 19th century, including adding interlocking flanges along all four sides, integrated backstops in the underlay portion of the shingles, and the addition of large, flat flanges along the edges of shingles that could be bent around eaves and valleys to act as integrated flashing.

Unfortunately these improvements weren’t enough to address the catch-22 situation faced by builders in Louisiana trying to protect buildings from frequent high wind and torrential rain.

Today, you might be surprised to find a building or two scattered around Louisiana communities that still have pressed metal shingles.

These two circa-1908 cottages on the corner of Laurel and 10th streets (formerly Pike Street) in Baton Rouge still retain their pressed metal roof shingles. They first appeared on the 1908 Sanborn Map. Photo by Adrienne Dickerson.

 

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