|The jetty seen on this house is created by projecting timber floor beams at first floor level.|
Traditionally, jettying was the art of creating overhangs as seen in timber-framed houses of the 14th to 17th centuries. The jetty (or jettie or jutty; derr. French ‘jeter’ to throw) refers to situations in which the upper floor overhangs the floor below by as much as 1,200mm (although usually around 400mm). If a house comprised two storeys above ground, the second storey would often overhang by as much as the one below.
 Reasons to jetty
Although the exact reason for jettying is not known, the most commonly-cited explanation is the need to provide extra space. While this is plausible – especially in the confined conditions of a medieval town – many of these buildings were in rural areas which did not have the same spatial constraints. In any case, the space provided by a modest jetty may not have yielded significant usable space.
Other possible reasons include:
- Fashion: If jettying originally started in towns, rural builders may simply have been keen to be seen ‘keeping up with the times’ and offering the latest building techniques.
- Structural 1: A heavy item of furniture in the middle of an upper floor room could, over time, cause sagging of the floor joists. By placing such heavy items in or close to the jetty – and therefore directly above or closer to the point where the joists bear on the wall below – much of the weight of the item is directed to the wall below and could also straddle over the wall.
- Structural 2: In a house with a two-storey central hall, jettying would require timbers only one-storey high, as opposed to timbers that extended right up to the eaves.
- Social status: Jettying was an added expense to the cost of building so having a jetty may have been a way of expressing the wealth of the householder.
- Weathering: These buildings seldom had eaves' gutters and downpipes so much of the water running-off the roof would flow down the walls. The inclusion of a jetty may simply have been a precaution against damp, protecting the lower floor from run-off.
 Related articles on Designing Buildings Wiki
- Advantages and disadvantages of timber frame buildings.
- Balloon framing.
- Delivering sustainable low energy housing with softwood timber frame.
- Sacrificial timber.
- Skeleton frame.
- Testing timber.
- Timber framed buildings and fire.
- Timber post and beam construction.
- Timber preservation.
- Types of frame.
- Types of timber.
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