What Is Jettying House? Advantages Of Jettying

What Is Jettying House? Advantages Of Jettying

What Is Jettying House?

Jettying is a building technique used in medieval timber-frame construction where an upper floor extends beyond the lower floor, allowing for extra space and not obstructing the street. This is known as a jettied floor or jetty.

A jetty is supported by a cantilever system where a horizontal beam, called a jetty bressummer, supports the upper floor and extends out further than the lower floor.

This structural feature can serve different purposes like increase space, counteract forces in the joists, protect lower walls from the weather, simplify joinery or serve as a status symbol.

Jettying was popular in the 16th century but banned in certain cities due to health and safety concerns. It’s considered a Gothic architectural style.

Advantages Of Jettying

The design of jettying has several benefits, such as maximizing the use of available land and providing shelter. Structurally, it also allows for more efficient use of floor beams.

Normally, beams have zero bending-moment forces at the ends, but in jettying, loading is arranged to maximize these forces at the center of the beam.

This reduces the necessary size of the beams and allows for more shallow beams, which saves space and cost. This design is responsible for the distinct architecture that can be seen in buildings throughout Europe, with upper floors protruding beyond lower floors and creating more space around buildings in towns and covered storage in rural areas.

Vertical Elements Of Jettying

In jetty construction, the vertical elements consist of large corner posts, called dragon beams which support the floor above and are supported by the floor below. These posts are located at the corners of the building.

Additionally, smaller studs, called close studding are used along the walls above and below the jetty. These elements can be seen in the examples of the Paul Revere House in Boston, MA and the hewn jetty in Glattfelden, Switzerland.

Horizontal Elements Of Jettying

The horizontal components of jettying include:

The jetty breastsummer, which is a support beam that spans the width of the jetty wall and rests on the sill.

The dragon-beam, which runs diagonally from one corner of the jetty to the other, supporting the corner posts above and being supported by the corner posts below.

The jetty beams or joists, which conform to the larger dimensions of the floor above and rest at a right angle on jetty-plates, which conform to the smaller dimensions of the floor below. The jetty beams are morticed into the sides of the dragon beams at a 45 degree angle and are the main components of the cantilever system, determining the extent to which the jetty projects.

The jetty-plates, which are designed to support the jetty beams or joists and are themselves supported by the corner posts of the recessed floor below.

It also mention that in french Jettying called as encorbellement, and it can be decoratively carved.

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