Dating building materials
They worked with five demolition and reclamation contractors three not-for-profits and two for profit to procure and test the materials, sourcing close to the project to reduce fuel consumption and saving the project time and money. Can't get enough TreeHugger? Sign up now and have it sent straight to your inbox. Daily and Weekly newsletters available. Email Address Email is required. Nathan Benjamin runs a dating service for materials, putting people together with the used. Related Content on Treehugger. Small carbon-neutral house in Australia built with recycled materials. Lofty eco-resort treehouse is built with locally sourced wood.
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Angular small house is inspired by Dutch and Japanese design. Artificial intelligence found a new species of hominids that bred with humans. Extinct tree grows anew from ancient jar of seeds unearthed by archaeologists. In research into our heritage the conservationist or architect may be able to date the general period of a building he is working with from either the situation, materials of construction, type of timber joints or other stylistic features.
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Almost certainly the century or portion of a century when it was built may be assigned with some certainty. However, as more and more work is done and increasing numbers of structures with complex constructional phases are encountered, the general features may not be sufficient to give the accuracy in dating that is currently required. If research into other sources of information also fails to throw light on the building's history, resort may be made to the various scientific methods of dating.
This article outlines three of the most important methods currently used for dating buildings or, in a complex situation, the order of construction within the building.
Each method has a distinct role in the investigation of historic buildings. None is infallible and before embarking on an extensive dating survey, due thought must be given to what might be achieved and which methods might be the more successful. If necessary, seek advice.
Whilst earlier types of wooden joints may be copied in later buildings and earlier styles may be reintroduced in later periods to confound the conservationist or historian, any reuse of older materials should become obvious by the use of the chronometrical methods described here. The incorporation of ancient bog oak into a building, no matter how intricately carved or jointed, would immediately become obvious to the chronologist, as would timber renovations. Dendrochronology is the oldest method, having been introduced over a century ago by an American astronomer, Professor A E Douglass.
He wanted to know whether the number of sunspots affected weather on Earth. If this were so, the width of the annual growth rings would show changes in synchronism with the sunspot numbers. He established a laboratory in the university of Arizona, at Tucson, to study tree-rings. Unfortunately, after many years of analysis he was not able to confirm the correlation he sought. Nevertheless, the laboratory was able to demonstrate many interesting properties of ring widths and their relationship with various aspects of climate and other natural phenomena and, of course, their use in the accurate dating of timber.
His laboratory is still one of the leading centres in world dendrochronology. It was not until that the science was taken seriously in Europe, mainly through the efforts of Professor Huber in Germany, and not until after World War II that such studies became established in the UK. The main centres in Britain researching this field are located at universities in Belfast, Cambridge, East Anglia, London, Nottingham and Sheffield with several freelance practitioners.
Whilst most dendrochronological research is still concerned with climatic change, where the precise dating provided by the growth rings is of vital importance, all units in this country are proficient in performing dendrochronological surveys of buildings. Oak is the species of prime interest and it is possible to date wood back to over 7, years with a precision, in appropriate circumstances, of a single year. 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.
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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.
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.
Dating Technology and Historic Buildings
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.
The core leaves a small hole in the timber of about 15mm in diameter which may be plugged with a timber dowel.
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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.