awning: A lightweight, roof-like covering – often made of canvas on a metal framework but also made of thin metal or plastic, with or without a frame – projecting from a wall, often above a window or door, to provide shade and protection from rain. Some awnings are fixed, and some awnings can be folded upward against the building.

breezeway: A roofed exterior passageway, open at the sides, connecting two separate structures.

butterfly roof: An inverted gable roof in which two sloping planes, each pitching downward from the eaves, meet in a valley.

cantilever: A structural element supported only at one end or the portion of a structural element extending past the last support. In the case of a horizontal beam or slab, the unsupported portion of the element that projects past a supporting column, wall, or beam.

concrete: A building material consisting of sand or other fine aggregate and gravel or other large aggregate bound together by an adhesive paste of cement and water. Formable when installed, concrete sets into a dense, rock-like mass. Concrete may contain additional ingredients that modify its properties. Often, concrete is incorrectly called 'cement," which is only one of its ingredients. See also reinforced concrete.

corrugated glass: A sheet of glass molded with a cross section in the form of a sine wave that can support more load and diffuses light more widely than flat glass of the same thickness. A method of making corrugated glass was patented in the United States in 1898.

curtain wall: A non-load-bearing exterior cladding – designed to support only its own weight and wind and seismic loads – supported by the building structure, often at every floor or at every other floor. Although curtain walls are made of many materials, including masonry, in Modern architecture they were often constructed of metal frames with glass lights and glass or metal panels.

exposed aggregate finish: A concrete finish in which the large aggregate – either typical washed gravel or more decorative crushed stone – is exposed by removal of the cement and fine aggregate from the surface of the concrete by brushing or pressure washing before the cement has set or by acid washing or light abrasive blasting after the concrete has cured.

fieldstone: Stones of a size useful in construction found on the surface of the soil that are generally flat in the direction of bedding. These stones are typically used for building walls.
flat roof: A roof either with no slope, called dead flat, or with only enough slope, generally one-quarter inch per foot, to cause water to run to drains, gutters, or scuppers.

float glass: Glass made by floating molten glass on a bed of molten metal. The glass, which has uniform thickness and flat surfaces, was developed in 1959. Float glass has completely replaced polished plate glass.

geodesic dome: A type of construction for enclosing a nearly spherical space using a frame constructed using a frame constructed of many similar, light, linear elements interconnected at nodes to form polygons that, in turn, form a three-way spherical grid, which is covered by a membrane or panels. The nodes are derived from a regular polyhedron projected onto a sphere. The structure was patented by R. Buckminister Fuller in 1954.

insulating glass units, IGU's,Thermopane, Twindow: Glazing units generally constructed of parallel sheets of glass, separated by space usually containing a partial vacuum or an inert gas, and bonded at the edges, which are installed to reduce heat transfer through glazed openings. Patents for insulating glass units were issued in the 1930s and the units were available in the 1940s.

light gauge steel framing, cold formed steel framing: Structural framing using relatively lightweight structural members, such as studs and joists, formed of galvanized sheet steel that are used in much the same way as dimensional lumber is used.

module: A dimension used to space structural elements and other building components so that elements of the building can be interchangeable to achieve economies of scale.

open web steel joists: Standardized, light-weight, shallow trusses used as joists, which were first manufactured in the early 1920s.

panel and batten siding: Wood siding consisting of plywood panels with wood battens applied over the vertical joints between them; similar to board-and-batten siding.

plate glass, polished plate glass: Clear glass, generally thicker than normal window glass, ground and polished on both sides to achieve optimum clarity and produce in large sheets for glazing curtain walls and window walls. Polished plate glass was available in the 1870’s. Modern houses with floor to ceiling glass were glazed with polished plate glass, which is no longer manufactured. Damaged and missing plate glass is often replaced with float glass.

precast concrete units: Masonry units made of concrete, sometimes reinforced, which are generally cast in molds and cured in a shop, allowing greater quality control than is possible when pouring concrete on site.

reinforced concrete: A composite material made of concrete, which is able to resist compression forces, and steel – usually in the form of rods, bars, or mesh – or another material that is able to resist tension forces. Reinforced concrete is most often employed as a structural material, but it can also be used for cladding and for decoration. It has been used in the United States since the last years of the 19th century.

reveal: A continuous groove between adjoining planar surfaces. In Modern architecture, reveals were often used at edges of building elements, such as walls and cabinets, to create the illusion that the elements are planes or solid objects floating in space rather than attached to adjacent building elements. Also, the continuous recess between a door or window frame and the surface of the adjacent wall.

ribbon window: A horizontal band of fixed or operable sash separated by mullions. Also, a horizontal band of lights separated by mullions or butt-joint glazed.

space frame: A three-dimensional, truss-like structural frame composed of relatively short linear elements joined together with connectors, which is most generally used to span wide spaces and is often covered with glass or with metal panels.

spandrel glass: Glass with an opaque or only slightly translucent colored coating, generally ceramic, fired on its rear face, which is used to glaze sections of wall to conceal structural members, mechanical equipments, and other building components. It is most commonly used to glaze spandrel panels of high-rise curtain walls. Spandrel glass was introduced in the 1950s.

suspended ceiling, hung ceiling, dropped ceiling: A ceiling, typically of plaster, gypsum board, or acoustical title, suspended below and generally supported by the structural ceiling above.

waffle slab: A two-way floor or roof system consisting of a reinforced concrete slab poured with integral joists or ribs in two directions beneath it. The system has a waffle-like pattern when viewed from below.

National Trust for Historic Preservation, 2009.