Shingles Eagle River AK
Certified Contractors Network (CCN)
Certified Contractors Network (CCN)
Introduction to Shingles
Pre-1900 shingles were traditionally made of wood, stone and metal. Shingles made of these solid natural materials are known to last for decades, even a century or more with proper maintenance. Since the late 19th century, manufacturers have been combining other materials to produce shingles, with the promise that they will last longer, look better, use fewer natural resources and cost less. Can they keep that promise? Sometimes.
Familiar asphalt shingles were once composed of felt or paper layers saturated with asphalt and covered with granules of stone. Throughout the 20th century, manufacturers refined and improved the shingles, with only occasional lapses in quality and performance (like the fiberglass shingle failures in the 1990s). While asphalt shingles typically last only 15 to 25 years, their low initial cost and a reasonable life-cycle cost make them a popular choice for the typical homeowner. There are other, less common types of composite shingles.
Most polymer shingles are made in molds taken from natural slate or cedar shingles so they look authentic.
Technology Portland cement binds together tiny cellulose fibers that act as reinforcements, like steel rebar in concrete, but on a much smaller scale. The mix of cement and fibers is cured in molds under pressure to form a variety of building products, including underground drainage pipes, boards, panels, siding and shingles. The shingles are durable to weather exposure for decades and resistant to fire. Some shingle products are formed and detailed to imitate traditional wood and slate shingles. Companies in Europe are even developing high-tech photovoltaic units bonded to fiber-cement shingles.
History Asbestos-fiber-cement shingles were first developed in France a century ago. New shingling systems and unique shingles were specifically designed to take advantage of this new material as it developed in the early 20th century. Those special diamond-shaped shingles were called diagonal-pattern or French pattern roofing and are now considered to provide architectural character to historic buildings of that era. Asbestos-cement shingles were common in the 1920s and 1930s. They were gradually phased out of production during the 1950s, 60s and 70s. In the 1980s, new shingle products were developed with fiberglass and cellulose from wood.
Performance The early products proved to have good performance and durability of 40 to 80 years. The more recent fiber-cement roofing products are still questioned by independent authorities such as the National Roofing Contractors Association. Some of the products were problematic, and thousands of roofs failed prematurely. During the 1980s and 90s several manufacturers moved in and out of the fiber shingle market, indicating that these newer products are still in a development phase.
Failure mode The early asbestos-cement shingles weather only slightly at the surface. They are quite brittle, making damage from tree branches or other falling objects common and repairs difficult. The recent fiber-cement shingles fail when the cement transfers moisture into the wood fibers, which then swell. Freezing can also damage the binding cement. Resin or paint coatings provide protection but increase the need for proactive maintenance. Birds peck at the failed coating, exposing the softer core, which then supports the growth of moss.
Environmental responsibility The early fiber-cement shingles were made from abundant raw materials, which were durable and saved other natural resources. Proper handling and disposal of the asbestos-containing shingles has become a costly health and disposal issue in recent years. If the current roofing manufacturers can develop their products to perform as well as the earlier ones without using scarce and polluting materials, then they may be able to measure up to the strong reputation of the earlier fiber-cement shingles.
Technology Particles are bound together with a plastic polymer resin such as polyethylene. Sometimes cellulose or fiberglass is added as reinforcement. A wide variety of materials are used for the particles, including pulverized natural stones such as slate, shale, limestone and clay. The stone acts as a low-cost aggregate and may help block ultraviolet radiation from the sun. Recycled materials may be added, such as shredded tire rubber to provide flexibility. Carbon black may be added to block UV rays to slow deterioration of the resin. The materials are heated and compressed into molds that imitate the shape and textures of traditional shingles like wooden shakes and slates.
History Production and availability of composite shingles is a recent development -- a matter of years, not decades.
Failure mode Considering the wide range of materials and formulations, chemical reactions within the shingles could occur and create the potential for deterioration. Ultraviolet light breaks down the binders, releasing the particles at the surface. The result is similar to paint that fails by whitening and chalking over time.
Environmental responsibility When the source of the resin binder used to make these shingles is recycled, they could be considered highly environmentally friendly. The variety of materials in the formulations may complicate the high-value recycling of installation waste and of the shingles at the end of their useful life.
Technology A plastic mixture of polymer resin, thermoplastic polyolefin (TPO), and lesser amounts of fillers are injected into molds under high pressure.
History These have been around for 15 years.
Performance These same plastic polymers have been used in the automotive industry since the early 1970s. Their performance and resistance to weathering are proven and well understood. If the shingle products are well engineered, they should last for decades. In the midterm (15 years) polymer shingles have proven themselves, but the actual long-term performance of these shingles is unknown.
Failure mode TPO is not a composite that can fail when its parts break down. It is a solid resin that is knitted together in long strands at the molecular level. Very limited UV breakdown takes place at the weathering surface.
Environmental responsibility Recycling is possible for shingles made of post-manufacturing recyclable rubber and plastic materials. High-value recycling at the end of the useful life of these shingles is engineered into the resin when TPOs are used.
John Leeke is a preservation consultant. More information on this and other topics can be found on his website at http://www.historichomeworks.com .