23 January 2022
“Dendrochronology dates the timber, not the building!” is a phrase that I have been confronted with several times on the threads of internet history discussion forums. I confess that the sentiment always takes me by surprise every time I encounter it. Dendrochronology is one of the oldest, most accurate and respected of the scientific dating techniques available to archaeologists. However, it seems that there are numerous folk out there who harbour the opinion that archaeologists are making it all up.
Fair acknowledgement here – I’m a buildings archaeologist by trade and have been involved in commissioning dendrochronology surveys on many occasions. Whether you think that means I am a secretive member of some shady cabal of archaeological illuminati is, of course, a matter between yourself and your gods. I can tell you one thing though – the financial benefits from such an organisation must be terrible because I’ve never seen a penny. Anyway…
How Dendrochronology Works
The science of tree-ring dating was first applied to archaeology during the early years of the twentieth century by A. E. Douglas. He realised that it was possible to calculate the year in which a tree was felled, and therefore when its timbers were used in a structure, through a careful study of its growth rings. The science is predicated on the fact that a tree adds a single growth ring to its circumference every year. The rings are intrinsically (but not exclusively) linked to the climatic conditions experienced by the tree – a cold year will limit the size of growth; a mild year will encourage growth. Trees of the same species, growing under similar conditions, within a limited region, at the same time will exhibit comparable patterns of growth. Given the presence of a sufficient number of rings in a sample (usually defined as more than 54 years) it is possible to identify a unique “fingerprint” which can identify the years in which the tree was alive and, potentially, when it was felled.
The trunk and limbs of a tree consist of three principal biological components: the bark, the sapwood and the heartwood. The heartwood is technically no longer living but contains the “fossilised” record of the tree’s growth ring pattern. The sapwood was still alive at the time of felling and may contain between 15 and 40 growth rings. The bark is the outermost layer of the tree’s tissues and, if still present, can potentially confirm the year of felling. The dendrochronologist will therefore hope to sample a building timber which has traces of bark, sapwood and heartwood – with at least 54 growth rings – to try and obtain a specific felling date. If the bark is no longer present, but part of the sapwood is, it is still possible to sample a timber to obtain a felling date range.
Samples are collected by drilling into the timber. The cores are then polished, analysed and compared to databases of known, overlapping, regional sequences which stretch back from the modern era deep into the past. So long as the dendrochronologist takes enough samples from the principal phases of construction, which can be compared to one another, it is possible to build up a site chronology.
Don’t just trust my word for any of this, though, here is a much better articulation of how dendrochronology works. It was written by Robert Howard and Alison Arnold of the Nottingham Tree-ring Dating Laboratory – an organisation with over 30 years of experience in the field.
The Objection to Dendrochronology
The principal objection to dendrochronology is summed up in the title of this blog article: “Dendrochronology dates the timber, not the building!” The inference is that all dendrochronology can do is tell us when the tree was felled, rather than when work on the building commenced.
Those who object to the accuracy of dendrochronology, in dating specific phases of construction, usually point towards the practice of using “seasoned” timber. They note that the timber may have been stockpiled in a yard for significant periods of time prior to purchase and use.
The assumption is that the modern-day timber industry was identical to that in the mediaeval or early modern periods: if the timber was stored for several years prior to construction, we cannot date the building according to the felling date.
Mediaeval Carpentry Practices
The key problem with the hypothesis of the previous section is that it is built upon the belief that modern carpentry practices are the same as they were in the past. Historic carpentry specialists, such as Dan Miles (2014, 12-14), have demonstrated beyond all reasonable doubt that mediaeval carpenters had a decided preference for working with freshly felled “green” timber. This was supple and could be worked or built with relatively easily.
Felled timber was not routinely “seasoned” for lengthy periods of time. There was no mediaeval facility to kiln-dry it (as in the modern era) and if freshly cut wood was air-dried (as it was during the industrial period) after a time it would twist and become unworkably hard. There was simply no advantage to a leaving a lengthy gap between felling and building – quite the reverse.
Now, it is true that there is limited evidence for imported timbers in the mediaeval period, but over 90% of all known building timbers were locally grown oaks (Rackham 1986, 86, 88). Fortunately, this species ideally lends itself towards dendrochronology. The specialists will identify timbers which represent the primary phases of construction. Usually, the dendrochronologists will avoid timbers which display evidence for secondary reuse – such samples would date a previous use rather than the structure in which they are now located. Although recycling occurred frequently, the fact remains that, in a new build, the mediaeval preference was for framing buildings with freshly felled “green” timber. This required large numbers of trees too – Mill Farm, Mapledurham (Oxfordshire) needed approximately 111 trees (Miles 2014, 81) and Grundle House, Stanton (Suffolk) required perhaps 332 trees (Rackham 1986, 87). Woodland management was a significant enterprise.
The belief that timber was “seasoned” in the mediaeval period is to engage in the dangerous habit of assuming that modern practices are the same as those in the past. Put simply – they are not, and we cannot project our world backwards with any hope of accuracy.
Archival Corroboration
Still don’t believe me? OK, let’s look at this another way. Dendrochronology is sometimes employed in buildings for which we have good surviving documentary evidence of construction. In most cases the archival evidence for construction exactly matches the dendrochronology. Examples of this include:
Timbers from the great tower and Middle Ward lodging range at Tattershall Castle (Lincolnshire) which had felling ranges dated to 1406-31 and 1446-51 respectively. The site has partially surviving building accounts from the period 1434-46 (Alcock & Tyers 2020, 129; Arnold & Howard 2017; Simpson 1960). The building accounts for the castle are incomplete – we do not have either the first or last years of work – meaning that the dendrochronology has helped to refine the specific dating of the castle to the period c 1431-51 (Wright 2021, 62-63).
Tree-ring dating for the roof structures of the Queen’s House at the Tower of London confirmed a felling date of 1538-39, which was backed up by archival evidence that construction was underway by June 1540 (Bridge & Miles 2015; Gregory 2014, 6).
The dendrochronology of the floor-frame of the King’s Tower at Knole (Kent), which had a felling date in the winter of 1605-06, was backed up by documentary evidence for construction work in the spring and summer of 1606 (Tyers 2014; Town 2010, 137-46).
Elsewhere, the very detailed building accounts of mediaeval structures clearly outline the streamlined process of felling, sawing, transporting and then building in timber. At Clipstone Palace (Nottinghamshire) repairs to the stew pond during the mid-fourteenth century necessitated 2 carpenters to fell, split and trim piles before placing them at the head of the pond. The entire job – from felling to completion – was specifically recorded to have taken no more than 2 days (Wright 2016, 130-31). Such documentary evidence once again indicates that there was no need to stockpile timber prior to construction.
Conclusions
A clear understanding of carpentry practices, when viewed in collaboration with surviving archival data, can help us to understand that (in most cases) new building projects in the mediaeval period required freshly felled timbers. The notion that “Dendrochronology dates the timber, not the building!” is flawed because it is based on a fundamental misunderstanding about historic construction practices. Timber was not stockpiled for long periods of time and was usually employed in buildings soon after felling.
We can therefore trust that the felling dates provided by dendrochronology will closely match the principal building phases of a structure. To quote dendrochronologists Robert Howard and Alison Arnold: “establishing the felling date for a group of timbers gives a very precise indication of the date of their use in a building.”
References
Alcock, N. & Tyers, C. (ed.’s), 2020, ‘Tree-ring Date Lists 2020’ in Vernacular Architecture Volume 51. Routledge. London.
Arnold, A. & Howard, R., 2017, The Guardhouse, Tattershall Castle, Sleaford Road, Tattershall, Lincolnshire – Tree-ring Analysis of Timbers. Unpublished archaeological report. Nottingham Tree-ring Dating Laboratory.
Bridge, M. & Miles, D., 2015, Queens’ House, Tower of London – tree-ring dating of oak timbers. Unpublished archaeological report. Oxford Dendrochronology Lab.
Gregory, A., 2014, The Queens House and Bell Tower – Statement of Significance. Unpublished archaeological report. Historic Royal Palaces.
Miles, D., 2014, The Medieval Peasant House in Midland England. Oxbow. Oxford and Philadelphia.
Rackham, O., 1986, The History of the Countryside. Phoenix Giant. London.
Simpson, W. D., 1960, The Building Accounts of Tattershall Castle, 1434-72. Lincoln Record Society No. 55. Lincoln.
Town, E., 2010, A House ‘Re-edified’ – Thomas Sackville and the Transformation of Knole, 1605-08. Unpublished doctoral thesis. University of Sussex
Tyers, I., 2014, Tree-ring analysis of timbers from a building: Knole, Sevenoaks, Kent. Unpublished archaeological report. Dendrochronological Consultancy Limited.
Wright, J., 2021, Tattershall Castle: Building a History. Unpublished doctoral thesis. University of Nottingham.
Wright, J., 2016, A Palace for Our Kings – the history and archaeology of a Mediaeval royal palace in the heart of Sherwood Forest. Triskele Publishing. London & Cheltenham.
About the author
James Wright (Triskele Heritage) is an award-winning buildings archaeologist who frequently writes and lectures on the subject of mediaeval building myths. He has two decades professional experience of ferreting around in people’s cellars, hunting through their attics and digging up their gardens. He hopes to find meaningful truths about how ordinary and extraordinary folk lived their lives in the mediaeval period.
He welcomes contact through Twitter or email.
The Mediaeval Mythbusting Blog blog is the basis of a forthcoming book – Historic Building Mythbusting – Uncovering Folklore, History and Archaeology which will be released via The History Press on 6 June 2024. More information can be found here:
