Cupolas are decorative and functional structures for a dome or roof. They are used for ventilation and architectural purposes. Cupolas have three sections: the base, the vents, and the cap with finial. As a rule, the base of a cupola must conform to the pitch or slope of the roof. Typically, the slope is expressed in inches of vertical rise per twelve inches of horizontal distance or run (e.g., 4/12). Cupola vents are slats or other external openings that permit the escape of gas or air. Sometimes, these vents are used in conjunction with screens to keep out animals and insects. Cupola caps have a distinct geometric shape. Examples include square, hexagonal, octagonal, and bell-like designs. The cupola finial is an architectural detail such as a knob, weathervane, or foliated ornament. Cupolas are made from wood, copper, vinyl, or composite materials. Many wooden cupolas are made of cypress, birch, oak, or white pine. Some have cedar shingles. Paint or stain can be applied to provide protection from the elements, or for aesthetic purposes. Copper cupolas are made from sheets of copper and provide long service life. Some are chemically-treated for a greenish finish. Others are designed to age naturally. Vinyl-clad cupolas are made of solid, expanded, rigid, polyvinyl chloride (PVC). Unlike wooden cupolas, they do not absorb moisture or de-laminate. They are also impervious to salt water and insects. Vinyl cupolas and cupolas made of composite materials can be painted, typically with an acrylic. Some cupola suppliers describe their products as belvederes, lanterns, and monitors. Belvederes or widow’s walks are rooftop cupolas that provide interior access. Lanterns have windows to admit daylight for illumination within the building. Monitors are low-profile cupolas that do not extend much beyond the roof. For each type of cupola, size and shape are important parameter. Square cupolas have a four-sided cap, hexagonal cupolas have a six-sided cap, and octagonal cupolas have an eight-sided cap. Ventilation is also an important consideration. High louvered products provide maximum airflow for applications that need to vent smoking from cooking. Replacement louvered side panels and weathervanes are available for some ornamental cupolas.