Built-in gutter systems are integrated within the cornice structure, connected to internal or external leaders, and are not readily visible. Traditional Rainwater Conductor Systems of the 18th and 19th Centuries by Karen Dodge of the National Park Service (1999) reports that built-in gutters were first adopted in North America during the 18th century in high-style Georgian and Federal-style buildings, usually public or commercial, where refined architectural qualities were desired. These hidden gutters also served an aesthetic purpose in buildings with grandiose compositions, classical orders, and elaborate cornices. The roof and cornice line are not only extremely important elements of the architectural character of these buildings — they also play a critical role in the water-shedding function of the exterior. Historically built-in gutters were constructed of wood boxes with sloped bottoms, lined with metal; the first metal linings were lead. Copper became available in America by the end of the 18th century and soon became popular for its durability. The integrity of the metal lining, flashings below the edge of the roof cladding, and cap flashings are critical to the performance of built-in gutters. A common sub-category of built-in gutter also called a boxed gutter, eaves trough, or sunken gutter, cuts through the roof itself and is lined with metal.
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