Until the 17th century England was blessed with an abundant supply of oak, which was the most common material used for timber framing.
Oak is hard and durable, which in part explains why so many medieval half-timbered buildings have survived.
The term "half-timbering" refers to the fact that the logs were halved, or a least cut down to a square inner section. In other areas of Europe, such as Romania and Hungary, there was no comparable hard wood available, houses were more frequently constructed using whole logs.
Unlike modern framed buildings where the walls are installed outside and inside the frame, in half-timbered buildings the walls are filled in between the structural timbers.
A perimiter footing of an impervious material like stone or brick was built first, then a sill beam laid on the footing. Upright beams were mortised into the sill beam and tenoned at the top into another horizontal member. Timber framed houses are essentially big boxes, with upper "boxes" (stories) set upon lower ones.
Often the upper floors project out over the lower ones. There are several conjectures as to the reasons for this. One is that houses in cities were taxed on the width of street frontage they used. So a high, narrow house saved the owner money, yet to maximize interior space the non-taxed upper floors were lengthened. Also, the projecting upper floors helped protect the lower house from rain and snow in the days before gutters and down-pipes.
By the 15th and 16th century timber framing began to be exploited for its decorative qualities. Timbers which had minimal structural importance were added to the frame, to enhance the decorative effect of dark wood set into whitewashed walls. The Jacobean period saw this use carried to extremes.
The construction methods used in half-timbering allow buildings to be easily dis-assembled and put up again elsewhere. This has helped salvage houses which would otherwise have been destroyed to make way for new development. Many medieval timber-framed houses have been re-erected at open air museums such as the Weald and Downland Museum at Singleton, West Sussex, and the Avoncroft Museum of Buildings at Bromsgrove, Worcestershire.
By the Jacobean period wood for timber framing was in short supply in England. For too many years wood had been used for building, heating, and for making charcoal.
By the way, the sloping, slanting, floors we see today in half-timbered buildings are not due to sloppy building practises, but a result of the natural warping of the wood as it aged. Also, the blackening of timbers was a natural aging effect. They were not treated or painted when built. It is only a desire of modern builders to provide a romanticised version of half-timbering that has produced imitation or black painted timbers.
Aside from the museums mentioned above, some of the best examples of half-timbered houses that visitors can see today are in the town of Lavenham, Suffolk, Little Moreton Hall in Cheshire, and Lower Brockhampton manor in Herefordshire. A personal favourite is Baddesley Clinton, near Solihull, West Midlands.