This is most impressive and makes dendrochronology the main dating method for structures containing oak timber. The method relies upon the response of trees to the weather during the growing season, which runs from March to October. In a 'good' growing season the trees within a large climatically homogeneous region all respond by putting on a wide growth ring within the cambium which separates the sapwood from the bark.

In a 'poor' growing season the trees all respond so that only a very narrow growth ring is formed. In more typical growing seasons a ring of intermediate width is produced. It should be noted that there is no direct linear relationship between ring width and, say, sunshine, or other weather components Thus a 'good' or 'poor' growing season is defined with reference to the amount of growth produced. For example, the year had a gloriously hot, long summer with most rainfall arriving in autumn but the trees did not appreciate it and all oaks produced a distinctively narrow ring.

Again the summer of was cold and wet, quite different from , yet the trees also produced a distinctly narrow growth ring. So it will be seen that seasons that are hot and dry as well as those that are cold and wet will produce a narrow ring so that such a ring is not diagnostic of the weather.

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Year by year the trees throughout the region produce a similar pattern of wide and narrow rings in response to the weather changes. It is this pattern that allows the accurate dating. The pattern of ring widths on a specimen taken from a building is matched, using a computer with a 'master chronology' often several centuries long for the particular area. This regional chronology will have been painstakingly built up from many thousands of measurements and by cross-matching many overlapping patterns of timbers.

The youngest patterns are obtained from living trees, where the felling date of the final ring is known. Progressively older patterns are obtained from trees in recent buildings, older buildings, archaeological sites and ancient bog oaks. Because of local, non-climatic causes of change of growth width, the chronologies around the country vary somewhat, and the best dating match is always obtained from a local regional master chronology. The dendro-date is thus the year in which the final ring of the specimen grew the year in which the tree was felled, but not necessarily the year in which the building was constructed.

In order to obtain an accurate match and hence a date, it is important to have at least 80 rings on the specimen that is to he dated. With fewer rings the pattern might have repeat matches at different points in the time scale and so give rise to multiple possible dates. This has implications for some vernacular structures in which rapidly grown, wide-ringed oaks, 30 to 40 years old, were used. In such instances it might be possible to date the wall plate which often contains far more rings.

In practice it is found that or growth rings are most likely to provide a unique match. However, because of the local ecological, non-climatic effects on the tree ring, it is not possible to guarantee that any particular specimen will give a date. In order to have greater certainty it is important to obtain several samples, in the form of cores drilled from the timber, and to construct a 'site chronology' for the building. The number of cores required will depend upon the complexity of the structure, but some ten cores per building phase is preferred.

These are normally taken by the dendrochronologist in co-operation with the historian and the position of the cores is carefully marked on the building plan for future analysis of the results.

Traditional Timber Framing - A Brief Introduction

The core leaves a small hole in the timber of about 15mm in diameter which may be plugged with a timber dowel. Although this method is capable of dating to the individual year, in practice several factors conspire to reduce the precision in dating the construction, sometimes drastically, and it is important to be aware of the limitations. Whilst in the middle ages it was the practice to use the timber 'green' - usually within a year of the felling date - in more recent times the timber is usually allowed to dry out, sometimes for decades, before use.

Furthermore, carpenters, aware of the effects of insect attacks, would deliberately remove the sapwood and even some heartwood.

The number of sapwood rings may vary between 15 and 50 years, depending on the position in and the age of the tree. Thus the year of the last ring dated could be misleading to the construction date and be underestimated by an unknown number, possibly 60 years. Sapwood may be found on at least some of the timbers in the dendrochronological survey and the site master chronology will lead to a more reliable date than an individual core.

Whereas tree-ring dating is limited in this country to oak structures, radiocarbon dating may be used for any wood species and, indeed, for any other organic based materials found in buildings such as: The range of radiocarbon dating reaches back to 60, years. For the last few thousand years it can have a precision of a few decades and may, in certain circumstances, be comparable with tree-ring dates. The laboratory at Cambridge here in England was among the first six to be set up anywhere in the world. There are now several radiocarbon dating laboratories in Britain including those at Belfast, Cambridge, East Kilbride, Oxford and Swansea, as well as a commercial unit near Harwell.

Radiocarbon dating is based on the element carbon, the basis of all life on earth. The atoms of this element are of three different types or 'isotopes'. They are identical chemically but have slightly different physical properties, particularly in mass. The isotopes are respectively 12, 13 and 14 times as heavy as the common hydrogen atom the base unit by which the weight of other elements is measured.

The isotopes C and C are stable and make up the bulk of the element, but the C isotope, which is mildly radioactive, is extremely rare.

1 The Beginnings of the Tradition

The instability of radiocarbon results in half of it disappearing in 5, years its 'half-life'. This instability is the basis of the dating method. All creatures have the same concentration of radiocarbon in their cells while they remain alive. This level is maintained constant by a sequence of events affecting the food web.

It starts with photosynthesis in green leaves of plants, whereby atmospheric water vapour and carbon dioxide, containing the radiocarbon, are combined in the presence of sunlight to produce sugar.

Dating Technology and Historic Buildings

The plant biological process converts this to the myriad of substances required for life. These substances are shared via the food network to all animals including man. For our purposes it may be assumed that the amount of radiocarbon in the atmosphere is constant over time. Once the creature dies the food chain is broken and the concentration of radiocarbon in the cells falls away. By measuring the residual C concentration in the material the date of its death may be calculated. Unique to this building type is the interlocking of the timber members of the roof trusses and supporting columns and their connection points.

The timber members are held apart by "fillers" blocks of timber. This leaves air spaces between the timber members which improves air circulation and drying around the members which improves resistance to moisture born decay. Timber members in this type of framing system were connected with ferrous timber connectors of various types. Loads between timber members were transmitted using split-rings larger loads , toothed rings lighter loads , or spiked grid connectors.

The rings were fit into circular grooves on in both timber members then the assembly was held together with through-bolts. The through-bolts only held the assembly together but were not load-carrying. Shear plate connectors resembled large washers, deformed on the side facing the timber in order to grip it, and were through-fastened with long bolts or lengths of threaded rod. In the United States and Canada , timber-frame construction has been revived since the s, and is now [ when?

Once a handcrafted skill passed down, timber-frame construction has now been modernized with the help of modern industrial tools such as CNC machines. These machines and mass-production techniques have assisted growth and made for more affordable frames and shorter lead-times for projects. Timber-framed structures differ from conventional wood-framed buildings in several ways. The methods of fastening the frame members also differ.

In conventional framing, the members are joined using nails or other mechanical fasteners, whereas timber framing uses the traditional mortise and tenon or more complex joints that are usually fastened using only wooden pegs. Recently, it has become common practice to enclose the timber structure entirely in manufactured panels such as structural insulated panels SIPs.

Although the timbers can only be seen from inside the building when so enclosed, construction is less complex and insulation is greater than in traditional timber building. SIPs are "an insulating foam core sandwiched between two structural facings, typically oriented strand board" according to the Structural Insulated Panel Association.

An alternate construction method is with concrete flooring with extensive use of glass. This allows a very solid construction combined with open architecture. Straw-bale construction is another alternative where straw bales are stacked for nonload-bearing infill with various finishes applied to the interior and exterior such as stucco and plaster. This appeals to the traditionalist and the environmentalist as this is using "found" materials to build. Mudbricks also called adobe are sometimes used to fill in timber-frame structures.

They can be made on site and offer exceptional fire resistance. Such buildings must be designed to accommodate the poor thermal insulating properties of mudbrick, however, and usually have deep eaves or a veranda on four sides for weather protection. Timber design or wood design is a subcategory of structural engineering that focuses on the engineering of wood structures.

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Timber is classified by tree species e. There are design specifications for sawn lumber, glulam members, prefabricated I-joists , composite lumber , and various connection types. In the United States, structural frames are then designed according to the Allowable Stress Design method or the Load Reduced Factor Design method the latter being preferred. The techniques used in timber framing date back to Neolithic times, and have been used in many parts of the world during various periods such as ancient Japan , continental Europe, and Neolithic Denmark , England , France , Germany , Spain , parts of the Roman Empire , and Scotland.

Its most northernmost areas are Baltic countries and southern Sweden.

Timber framing is rare in Russia, Finland, northern Sweden, and Norway, where tall and straight lumber, such as pine and spruce, is readily available and log houses were favored, instead. Half-timbered construction in the Northern European vernacular building style is characteristic of medieval and early modern Denmark, England, Germany, and parts of France and Switzerland, where timber was in good supply yet stone and associated skills to dress the stonework were in short supply.

In half-timbered construction, timbers that were riven split in half provided the complete skeletal framing of the building. Europe is full of timber-framed structures dating back hundreds of years, including manors, castles, homes, and inns, whose architecture and techniques of construction have evolved over the centuries.

In Asia, timber-framed structures are found, many of them temples that have stood for centuries. Some Roman carpentry preserved in anoxic layers of clay at Romano-British villa sites demonstrate that sophisticated Roman carpentry had all the necessary techniques for this construction.