This post is part of a monthly series that explores the historical applications of building materials and systems, using resources from the Building Technology Heritage Library (BTHL), an online collection of AEC catalogs, brochures, trade publications, and more. The BTHL is a project of the Association for Preservation Technology, an international building preservation organization. Read more about the archive here.

The role of the roof cannot be understated. It shelters a building’s interiors and its occupants from the forces of nature, protects vital utility systems, and helps to define the exterior’s aesthetic. The roof’s necessity has bred its ubiquity and, by extension, fostered a strong market for roofing materials ranging in performance and physical characteristics.

Those materials have a long history, and their evolution has been largely driven by performance. Wood and slate shingles and clay tiles were the predominant roofing choice until the mid-19th century, when metal and bituminous roofing systems made low-slope applications possible. During the 20th century, several new materials were developed for low- and steep-sloped roofs. Among them was the asphalt shingle, which arrived on the scene around the turn of the 20th century and continues to be the top roofing material for houses. After a period of market experimentation with various shapes, patterns, and textures, the asphalt shingle evolved in form to the three-tab version popular today.

Composites, such as asbestos and fiber-cement, rivaled asphalt for a time by purporting better performance while attempting to replicate traditional materials such as slate or clay tile. Imitation subsequently became a theme in the roofing category, with early examples including metal shingles that replicate the look of clay tiles and asphalt shingles that simulate thatching. The 20th century also saw the development of roofing materials with various levels of durability and fire resistance as well as the introduction of roof-related components such as gutters, downspouts, and flashing.

The following brochures, pamphlets, and journals from the digital Building Technology Heritage Library explore how roofing systems evolved throughout the 20th century.    

“Ancient” Tapered Mission Large, Ludowici-Celadon, 1925: Clay tiles are one of the oldest forms of roofing that are still available today in their natural form as well as in synthetic imitations. This Ludowici-Celadon catalog from the mid-1920s notes the material’s origin in the Mediterranean—its so-called “ancient” roots—referencing clay tiles’ popularity in that style of residential architecture.
   
    
H.M. Reynolds Shingle Co., 1910: The H.M. Reynolds Company of Grand Rapids, Mich., claimed in the early 20th century to have invented the asphalt roof shingle. As with many now-ubiquitous products, this is difficult to prove. However, rolled asphalt roofing coated with slate granules was available by the late 19th century so it’s not a stretch to see how the material could have been used to make individual shingles soon thereafter—it also makes it even more difficult to nail down who, exactly, did it first. Asphalt shingles were widely available by 1910 and rapidly replaced wood shingles due to their economy and fire resistance. Throughout the 20th century, the asphalt shingle evolved to include a range of shapes and textures with the crushed slate coating replaced by ceramic granules. 
       
         
Penrhyn Stone: Slate Roofs of Quality, J. W. Williams Slate Co., c. 1930: Slate has long been a regionally prominent roofing material in the northeastern U.S. and nearby parts of Canada because of the abundance of slate quarries in the area. Slate also became popular in the rest of the U.S. in period styles of residential and commercial architecture. The material's extreme durability made it popular with institutional owners. It is also quite heavy, suiting it for steep, rather than shallow, roofs. Of the limited range of slate colors, red is the rarest and is therefore typically used for ornamental accents.
     
            
Barrett’s Hand Book on Roofing and Waterproofing for Architects, Engineers, and Builders, Barrett Manufacturing Co., 1896: The development of built-up roofing—comprising alternating layers of asphalt-impregnated fabric and bituminous coatings—changed the shape of buildings, quite literally, in the temperate regions of the U.S. The steep-slope roof was no longer necessary for rain protection, and the resulting flat roofs would forever change the scale and appearance of the built environment. The Barrett Manufacturing Co., in New York, was a major producer of built-up roofing materials, and the BTHL features the company’s technical catalogs from the 1890s through the 1950s.
    
      
Republic Steel Roofing Products, Republic Steel Co., c. 1939: Large steel roofing panels were particularly popular for agricultural and industrial buildings. Corrugations allowed panels to span longer distances, which reduced the material volume and framing weight, while galvanized coatings gave the panels a longer service life. The material, which originated in the 19th century, remains widely used today.
         
             
Certigrade Handbook of Red Cedar Shingles, Red Cedar Shingle Bureau, 1957: Cedar shingles commonly topped residential structures through the 19th century but were supplanted in popularity in the 20th century by asphalt. The shingle typology has been revived in the 21st century for roofing and siding applications, typically in higher-end projects.  
            
        
The Book of Roofs, Johns Manville, 1923: The combination of asbestos and cement resulted in fiber cement, which, when applied as roofing shingles, made for an extremely durable product weighing significantly less than clay and slate tiles. Fiber-cement shingles that simulated the look of slate and clay were particularly common. One popular variation was a large-scale hexagonal form-factor that produced a distinctive pattern.  
     
            
Sheet Metal Building Materials, W. F. Norman Manufacturing Co., 1936: Stamped sheet metal roof tiles made to simulate clay tile were popular in the early 20th century. The W. F. Norman Manufacturing Co. of Nevada, Mo., was an early producer of the product and still makes two simple versions of the metal roof tiles.