23 January 2022 [edited 27 August 2025]
“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. Alternatively, some will assume an online “Gotcha!” moment by demanding: “How do you know the timbers aren’t re-used!?” I confess that these doubting sentiments often take me by surprise. This is because 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 Objections to Dendrochronology
One of the principal objections to dendrochronology is summed up in the first line 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.
Others loudly insist that it is impossible for us to be certain that the timbers are not reused. Some go on to say that it is not possible to be 100% certain that a timber was cut down specifically for use in that building and therefore the whole process is undermined – the building cannot be dated. I will deal with both points in the next two sections of the blog.
Mediaeval Carpentry Practices
The key problem with the hypothesis that the timber may have been stockpiled for many years 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 (see below for more on this). 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.
Re-used Timber
It is acknowledged that timber can be re-used. I have surveyed many examples of this occurrence. Examples include re-used timbers associated with a wellhouse at Hungerford Park (Berkshire), reused timbers in the roof structure above the Venetian Ambassador’s Bedroom at Knole (Kent), and Griggs Farmhouse at Bulmer Street (Essex) which appeared to be constructed almost entirely from re-used timber. In each case there were clues that the timbers had been re-used.
At Hungerford Park, many timbers in the wellhead structure featured relict mortises and severed tenons in timbers which had been dislocated from their initial construction. The joints were no longer fulfilling their original function and the archaeology of the timbers indicated that they were not in their primary setting. This is perhaps the most common clue towards timber re-use.
Relict mortise with a partially severed tenon still in situ in a re-used timber at Hungerford Park, Berkshire (Picture Source: James Wright / MOLA)
Meanwhile, at Knole the clues came from double-coded carpenter’s assembly marks on the rafters of the roof structure. When historic carpenters converted freshly felled timber in the framing yard they would mark up the joints with sub-Roman numerals so that they could understand how to piece together a frame on site i.e. peg the tenon on the collar marked II into the mortise joint on the rafter marked II. At Knole, many of the roof timbers had their original assembly marks visible but the same timber would also have secondary marks, on them e.g. rafters marked with VII and ≠; V and XIIII; III and ≠I; IIII and IIIIλ; VI and ≠. The marks on the timbers were not in numerical sequence and many were were double-coded. This would tend to indicate that the timbers had been re-used at least once and were not in their primary setting.
Rafters at Knole which have double-coded and out of sequence carpenter’s assembly marks (Picture Source: James Wright / MOLA / National Trust)
The house at Bulmer exhibited evidence of relict mortise joints, out of sequence carpenter’s assembly marks, and also timbers which were clearly not in their original setting. For example, a cranked tie beam, from what may once have been a crown post roof, had been reused as a cill beam.
Tie beam reused as a cill beam at Bulmer, Essex (Picture Source: James Wright / Triskele Heritage)
I have seen similar re-use elsewhere. At Greasley Castle Farm (Nottinghamshire) bridging beams from floor frames were re-used as lintels above windows and as principal rafters in the roof. At Winchester City Mill (Hampshire), a crown post from a roof structure had been re-used as a post to support the floor frame. An extreme example of this practice is the possible ship’s mast which has been incorporated as a tie beam at Waxham Great Barn (Norfolk). Please note, though, that the re-use of ship timbers in historic buildings is an incredibly rare phenomenon which was not nearly common as assumed by the public at large. For more information on the re-use of ship timbers please see the Mediaeval Mythbusting Blog #13.
The point to make here is that re-used timbers will usually display some material evidence that they are not in their primary location. Some might go on to query if we can still be sure when looking at a timber with no obvious physical evidence for its prior function i.e. relict joints. It is, of course, possible that there may well be a plain sawn or split timber which (at first glance) may not be obviously re-used. However, prior to sampling, we will take great care to ensure that the selected timber really does seem to be part of the primary frame, that it appears to have been built using green oak, that it is of the same species as the rest of the frame, that the toolmarks and patina are similar to the surrounding timbers.
Sometimes, mistakes can still be made but these are usually recognisable. Dendrochronologists will aim to take multiple samples from the primary frame to ensure statistical accuracy. For example, during the survey of Hall Barn at Dronfield (Derbyshire) 13 samples all aligned to indicate a single felling date, for the roof structure, of 1429. Meanwhile, the survey of Bromley House Library at Nottingham (Nottinghamshire) revealed that 14 out of 16 samples from the floor frame and roof structure all agreed a felling date of 1747. This corresponded with the archivally documented construction of the building (see below for more on Archival Corroboration). However, two timbers from the floor frame dated to 1549 and 1652 respectively. These two timbers were interpreted as re-used. Their anomalous dating showed up clearly because the dendrochronologists had sampled enough timbers and the vast majority of them indicated a single phase of felling in 1747.
Prior to selecting locations for tree-ring sampling, buildings archaeologists and dendrochronologists are at great pains to ensure that the timber was freshly felled for insertion into the primary frame. Ideally, multiple samples will be taken from as many timbers in the same frame to ensure statistical 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 1425-51 (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. Furthermore, it is not standard practice to randomly date timbers. Great care is taken to ensure that a sufficient number of samples are taken from timbers that are in their primary setting.
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 respectful contact through email or on Twitter, Instagram & Bluesky
The Mediaeval Mythbusting Blog is the basis of the book – Historic Building Mythbusting – Uncovering Folklore, History and Archaeology which was released via The History Press in June 2024. More information can be found here:
