Why the “Jetty” for an Upper Floor
Have you ever wondered why some of the old European cottages, which have more than one story, have successive cantilevered floors (”jettied”) which give them a “top heavy” look?
Originally, during the Middle Ages, when additional stories to cottages or buildings were built, cottage builders first used relatively flat floor joists which were laid directly on top of the walls below, creating flat exterior (normal looking with no cantilever) walls. These second and third story floors however, would sag and shimy from loads placed upon them, such as when furniture was placed upon them or by people walking around on them.
It was not until the 17th Century that builders discovered that if the ends of these joists were projected out beyond the story wall below by two feet or so, and that the upper story wall was then built out on the ends of these joists, the weight of the upper part of the cottage would then stablize the floors and act as a counterpoise for any weight placed upon the floor joists. This proved to counteract the sagging by creating a “load deflection” as it is called in modern building terms. Therefore, each additional story was built successively “jettied” out from the floor below which created a “top heavy” look to many cottages and buildings of that time.
Our modern day floor joists have been designed in such a way that “jettying” is no longer required. However, these modern day joists do have a slight crown (although not very easily seen or felt it is so slight) which is designed into the joist so that the joist will level off, flatten, and NOT sag when loads are placed upon them, unless of course too heavy of a load is placed on them.
mattc 5 Oct 2006
Very informative. I hope you continue to post interesting facts like this, it is fascinating to learn how architecture has evolved over the centuries.
Do you ever purposefully make your designs top heavy to mimic the 17th Century feel?
samuelh 5 Oct 2006
Yes, some of our cottages have these jetties because we love this look. We’ve even designed in some off-camber or slightly “crookedy” or swayed design elements, such as crooked or wavy exterior timbering and swayed roof-lines, on some of our cottages to emmulate the authenticity of these quaint old cottages.
Otey C. Reynolds 28 Oct 2006
I thought houses were jettied because the property taxes at the time were based on size of the dwelling at street level.
samuelh 2 Nov 2006
Thanks Otey for your comment. The cottages may have been taxed according to theirs size because I have also heard that these old cottages were taxed according to the amount of window area each one had. Glass was expensive and if you take a look at the old images, some of the glass is irregular and contains imperfections. Thus, the more affluent had better glass and could afford more of it. I’ll look it up and find some more details on this.
See our Article “Old glass windows; solid or liquid” for more interesting comments and conversation about old windows and glass.
Derek Hurd 7 Nov 2006
I have also heard that the leaded glass windows of the age were difficult to seal and the overhang offered some protection to the main floor windows from the rain.