Jettying (jetty, jutty, from Old French getee, jette) is a building technique used in medieval timber-frame buildings in which an upper floor projects beyond the dimensions of the floor below. This has the advantage of increasing the available space in the building without obstructing the street. Jettied floors are also termed jetties. In the U.S., the most common surviving colonial version of this is the garrison house. Most jetties are external, but some early medieval houses were built with internal jetties. Structure A jetty is an upper floor that depends on a cantilever system in which a horizontal beam, the jetty bressummer, supports the wall above and projects forward beyond the floor below (a technique also called oversailing). The bressummer (or breastsummer) itself rests on the ends of a row of jetty beams or joists which are supported by jetty plates. Jetty joists in their turn were slotted sideways into the diagonal dragon beams at angle of 45° by means of mortise and tenon joints. The overhanging corner posts are often reinforced by curved jetty brackets. The origins of jettying is unclear but some reasons put forward for their purpose are: to gain space. the structural advantage of the jettied wall counteracting forces in the joists or tying a stone wall together to shelter the lower walls of the house from the weather. to simplify joinery. uses shorter timbers, a benefit due to timber shortages and difficult handling of long timbers especially in city streets. as a status symbol or "...symbol of wealth and status." Jetties were popular in the 16th century but banned in Rouen in 1520 relating to air circulation and the plague, and London in 1667 relating to the great fire. They are considered a Gothic style. Structurally, jetties are of several types: framed on multiple joists. framed on a few beams. framed on brackets added to the posts. hewn jetty also called a false jetty: Framed on projections of the posts rather than on cantilevered beams (or brackets). Vertical elements The vertical elements of jetties can be summarized as: the more massive corner posts of the timber frame that support the dragon beam from the floor below and are supported in their turn by the dragon beam for the extended floor above. the less substantial studs of the close studding along the walls above and below the jetty. Horizontal elements The horizontal elements of jetties are: