As well as the primary construction units, the house shows evidence of alterations in 1719-26 by Thomas Daunt, notably involving the raising of the ceiling in the SE first floor room (part of Unit A), and in 1926 by Norman Jewson, the Arts-and-Crafts architect.
Each is described in summary below.
The house is notable for the number of early doorways it contains, though it appears that not all are primary features of the units that include them. They have only been briefly studied. The painted cloths, which are particularly notable feature of the house, are not discussed here.
Unit A.
The roof structure gives the clearest picture of this unit. It has four trusses, numbered with carpenter’s marks / to ////, at each end of the collar, with the western side distinguished by tags. The northernmost truss comprises principal rafters and a collar, presumably standing on a tiebeam which is chamfered only on the southern side [collar also chamfered on one side only?], implying that it stood against a stone wall at the N end of this range; this wall was probably removed when Unit C was added. The southernmost truss, standing against the S gable (with evidence for a blocked window in the gable), is similar, though the tiebeam must have been removed when the ceiling of the first floor chamber here was raised. Each internal truss has two chamfered arch-braces meeting at a central block tenoned to the collar (curiously, both these blocks are off-centre). With one exception, these braces fill the angles between collar and principal, and their grain closely follows their curve. Presumably as a result, they do not have the usual tenons into the principal and collar, but use double-pegged slip tenons. The exception, the brace on the N side of truss III, must have been cut from a straighter timber, does not fill the angle, and has standard tenons. Truss III stands on a ceiling beam and can definitively be shown to be contemporary with this beam, since the surface of this beam (badly decayed) carries the same carpenter’s mark (///+tag) as the collar. It also clasps a diagonally-set wallplate. The roof has double purlins butt-jointed into the principals (with a complex double mortice and originally had windbraces, most [all?] of which have been removed.
As well as the two surviving beams carrying trusses III and IV, and those cut off by the raised ceiling of the southern room, two intermediate beams survive; all these beams are chamfered with bar stops. The presence of these intermediate beams indicates that unit A was undoubtedly floored at the level of these tiebeams and was therefore of three storeys. The decorative nature of the trusses suggests that this area was of relatively high status, and use as something equivalent to a long gallery is possible. [Long galleries as such only appear in the mid-16th century, though similar rooms are recorded earlier.
The original layout of this unit at first floor level is unknown. After the 18th century alterations, it was divided on the line of the central (intermediate) tiebeam. At ground floor level, it seems to have had a cross-passage for which the head of the original rear doorframe survives [and the front doorframe?]. This unit included a circular stair, which presumably originally rose to the third floor, but was altered when the wall between units A and C was removed; the passage was blocked by a wall at some stage, although the blocking and the stair were completely removed in the 1926 alterations. The position of this cross-passage, very close to the end of the unit, suggests that a predecessor to unit C already existed and that it included a doorway into this range from the passage.
On the south side, a fine door, with round-and-hollow moulding and converging stops leads down steps into the southern rooms in this unit. The position of the chimney suggests that originally this may have been a single room, but in the 18th century the Little Parlour occupied the southern two thirds of this space. The floor level was raised in 1926, but previously it had been substantially below the level of the cross-passage and somewhat below that of unit B.
Tree-ring dating of Unit A (see second part of report for technical details)
Samples were taken from five timbers in this range, of which four were successfully dated. The most remarkable is perhaps owl1, though it is of little direct significance for the development of the existing building. This came from the lower purlin on the west side in the southernmost bay, which was felled between 1294 and 1326 – this was undoubtedly reused, perhaps (though not demonstrably) from an earlier building on the site. Sample owl5 was felled in Spring 1539, and the dates for the two samples owl2 and owl4, which do not have complete sapwood, are consistent with this. Thus, the construction of this unit is firmly dated to 1539, or within a very few years of this.
Unit B.
Like unit A, this block has three storeys. The roof uses collar trusses with similar carpenter’s marks to those in unit A, though they are not arch-braced; again, they probably stand on tiebeams, though this has not been confirmed. Truss BIII (W. of the gable) has an extended collar, to support the gable – a typical Gloucestershire feature – that demonstrates both that this range was built with three-storeys, and that the gable is original. It is not clear why the adjoining truss BII does not also have an extended collar. It has single purlins (though a lower purlin may be concealed) and ogee windbraces.
The large ground floor room, undoubtedly the hall, has a compartmental ceiling with large chamfers to the heavy beams. The axial beams are primary, with the transverse beams joining them with scribed mitres (apart from the north side beam, which has masons mitres). The beams terminate on a heavy transverse beam 8 ft from the east wall of the hall (and with the ceiling plastered in this gap). This pattern strongly suggests that a partition originally stood under this beam, although whether this defined a very wide passage or a small room is unclear.
Tree-ring dating of Unit B
The dating evidence for this unit is complex. Five samples were taken, of which four gave dates. The most straightforward to interpret is owl14, from the valley rafter between the main and dormer roofs, which was felled in Spring 1586. With this, as indicating a building phase, we can take owl11, from the heavy transverse ceiling beam just mentioned, felled in Spring 1584. These two dates are taken to indicate that this range reached its present three-storeyed form in 1584-6 (perhaps finally roofed in 1586). However, as suggested by the architectural analysis, the compartmental ceiling over the west part of the hall is substantially earlier than this main beam, with sample owl12 giving a felling date range of 1514-38. Perhaps to be associated with this is the date from owl15, the collar of Truss BI, felled in Summer 1541. This must be re-used in its present position in the 1580s roof, but perhaps indicates the date of an earlier roof for this range.. This date might be related to that of the compartmental ceiling, although it falls slightly outside the latter’s felling date range; however, the most likely date within that range is around 1520-5, and the wide rings are more likely to indicate relatively few rather than exceptionally many sapwood rings. Thus, an interpretation is preferred in which these two dates represent separate phases. It is also possible that the 1541-dated timber might have originated somewhere in unit A, as part of the c. 1539 work.
An interpretation of unit B can be suggested that is speculative in parts:
Date Event
pre-1520 Medieval open hall
c. 1520-5 Ceiling inserted in hall
c. 1541 Re-roofed shortly after completion of new low-end wing (Unit A), possibly three-storey, more likely two-storey
c. 1584 Cross-passage widened and reconstructed
c. 1586 Re-roofed with three-storeys
West end of Unit B.
At the west end of Unit B, the doorframe has a roll and hollow moulding, similar (but not identical) to that in unit A; it has spandrels decorated with leaf-patterns and uses mason’s mitres. This almost certainly pre-dates the 1616 parlour wing to which it leads, and indicates the former presence of an earlier range here. Similarly, the fireplace here is of an earlier form than that in the 1616 block.
At first floor level, the rear passage may well be an alteration dating from the addition of unit D and its stair, a possibility consistent with the position of the fireplace in this first floor room, which is now well off-centre.
Unit C.
This represents an extension to unit A, whose building involved the removal of the latter’s north wall. On the ground floor it contains a very large fireplace with (before the 1920s alterations) an oven at each end (or an oven and a copper). The two transverse ceiling beams have substantial chamfers and straight-cut stops, possibly dating from the end of the 16th century. It has no visible original roof structure, and no samples suitable for tree-ring dating could be located. From this limited architectural evidence, this could well correspond in date to the insertion of the heavy ceiling beam in unit B.
Unit D.
This handsome three-storey parlour block was built in 1616, according to its datestone. It includes a striking full-height bay window (reduced in width at gable level), clearly original as it is integrated with the string courses. It includes a very fine newel stair leading at first-floor level to a pair of doors to the passage and room over unit B, and to a second pair leading into the two first floor rooms in this block. The latter are undoubtedly secondary, as the division into two rooms partly blocks one of the windows of this space (though one of the doors is probably an original part of the unit, leading off a lobby at the stairhead. A similar division at the foot of the stair is probably also secondary.
The ground floor fireplace has a ‘Tudor’ arch with vase stops, typical of the early 17th century.
Unit E.
This lean-to seems to overlap the junction between units A and C, suggesting that its original purpose was for covered communication between the kitchen and the hall. Apart from being necessarily later than unit C, it contains no features that would indicate its date. It was apparently single-storeyed, but was adapted and raised in 1926 alterations to hold an improved staircase.
Overall development
A possible interpretation of the development of Owlpen Manor is as an example of ‘alternate development’.
1. The house may have originates as a now-vanished medieval hall on the site of unit B with chamber/parlour to the east, cross-passage and service to the west.
2. A ceiling was inserted in the hall in 1520-5.
3. The chamber end of this range was replaced in c. 1539 by a smart three-storey parlour block with chamber and gallery over.
4. In c. 1541, the hall range was re-roofed.
5. In 1584-6, the hall range was reconstructed as the present three-storey block. A new cross-passage was inserted at the east end of unit B (replacing a cross-passage on the site of unit D. New front and rear doors were inserted in their present positions, thus reversing the ‘ends’ of the house.
6. At the same date, or rather later, the rear wall of unit A and whatever stood beyond it was replaced by a new kitchen (unit C). At this stage (or later), the lean-to was added to improve communication between the kitchen and the hall.
6. In 1615, The service end associated with unit B was replaced by another smart three-storey parlour block – unit D.
The barn
A notable feature of the site is the barn, with five raised-cruck trusses. All [those seen] are arch-braced and have central blocks of a curious bulbous shape. Blocks are also tenoned into the blades below the end of the braces, as if to support them, though they can hardly have been of practical use for this; it seems very unlikely that they are remnants of cut-off tiebeams. The blades are supported on substantial flat wooden blocks and carry dovetail-halved spurs.
The barn has not been dated, but a mid-15th century date would be plausible – a date of somewhat after the acquisition of the manor by the Daunt family in 1462 would be plausible.
Oxford Dendrochronology Laboratory
Report 2009/17
The Tree-Ring Dating of Owlpen Manor,
Dursley, Gloucestershire
Dr D W H Miles FSA
Summary:
OWLPEN, Owlpen Manor (ST 800 982)
(a) East range Felling date: Spring 1539
(b) Hall ceiling Felling date range: 1514-38
(c) Hall range roof phase 1 Felling date: Summer 1541
(d) Hall range reconstruction and roof Felling dates: Spring 1584 and Spring 1586
(a) Intermediate ceiling beam 1538(20¼C); Collars 1513(2), 1520(H/S); Lower purlin (reused) 1285(H/S); Rafter (0/1). (b) Joist 1513(16). (c) Collar 1540(19½C); (d) Ceiling beam 1583(24¼C), Valley rafter (1585(20¼C); Principal rafter(0/1). Site Masters (a) reused purlin 1196-1285 owl1 (t= 8.6 KGWBSQ01; 6.8 WNTERBRN; 6.3 omw5); (b) 1424-1585 OWLPEN (t = 10.2 MASTERAL; 9.9 HANTS02; 8.8 SALOP95)
Owlpen Manor is a romantic stone-built Cotswold manor house with a complex development. Four principal structural units can be identified in its plan. These comprise: (1) a three-storey hall block oriented E-W, that reached this form in c. 1586, the date of the roof structure. This has a large dormer, supported by an ‘extended collar’ truss. A reused collar may be associated with a reconstruction of the roof in c. 1541. The compartmental hall ceiling may have been inserted into the predecessor of this hall in about 1520-5 (felling date range 1514-38); what is apparently a cross-passage beam has been dated to 1584. (2) A three-bay three storey block at the east end of the hall, oriented N-S. apparently a parlour block with chamber and gallery over, is dated to c. 1539. The four arch-braced trusses stand on tiebeams. (3) A kitchen, added behind the parlour block, probably in the later 16th century. (4) A three-storey parlour block with a datestone of 1616, built at the west end of the hall, probably replacing an earlier service unit. The house was altered in 1719-26 by Thomas Daunt, notably involving the raising of the first floor ceiling in part of the 1539 parlour block, and in 1926 by Norman Jewson, the Arts-and-Crafts architect.
Date sampled: 14th June 2009
Owner & Commissioner: Sir Nicholas Mander
Historical Research: Dr Nat Alcock FSA
Summary published: Miles, D H, Worthington, M J, and Bridge, M C, 2010 Tree-ring dates, Vernacular Architecture 41, (forthcoming)
Oxford Dendrochronology Laboratory
Mill Farm, Mapledurham, South Oxfordshire, RG4 7TX
daniel.miles@rlaha.ox.ac.uk & michael@dendrochronology.com
www.dendrochronology.com
September 2009
How Dendrochronology Works
Dendrochronology has over the past 20 years become one of the leading and most accurate scientific dating methods. Whilst not always successful, when it does work, it is precise, often to the season of the year. Tree-ring dating is well known for its use in dating historic buildings and archaeological timbers to this degree of precision. However more ancillary objects such as doors, furniture, panel paintings, and wooden boards in medieval book-bindings can sometimes be successfully dated.
The science of dendrochronology is based on a combination of biology and statistics. Fundamental to understanding how dendrochronology works is the phenomenon of tree growth. Essentially, trees grow through the addition of both elongation and radial increments. The elongation takes place at the terminal portions of the shoots, branches, and roots, while the radial increment is added by the cambium, the zone of living cells between the wood and the bark. In general terms, a tree can be best simplified by describing it as a cone, with a new layer being added to the outside each year in temperate zones, making it wider and taller.
An annual ring is composed of the growth which takes place during the spring and summer until about November when the leaves are shed and the tree becomes dormant for the winter period. For the European oak (Quercus robur and Q. petraea), as well as many other species, the annual ring is composed of two distinct parts - the spring growth or early wood, and the summer growth, or late wood. Early wood is composed of large vessels formed during the period of shoot growth which takes place between March and May, which is before the establishment of any significant leaf growth, and is produced by using most of the energy and raw materials laid down the previous year. Then, there is an abrupt change at the time of leaf expansion around May or June when hormonal activity dictates a change in the quality of the xylem and the summer, or late wood is formed. Here the wood becomes increasingly fibrous and contains much smaller vessels. Trees with this type of growth pattern are known as ring-porous, and are distinguished by the contrast between the open, light-coloured early wood vessels and the dense, darker-coloured late wood.
Dendrochronology utilises the variation in the width of the annual rings as influenced by climatic conditions common to a large area, as opposed to other more local factors such as woodland competition and insect attack. It is these climate-induced variations in ring widths that allow calendar dates to be ascribed to an undated timber when compared to a firmly-dated sequence. If a tree section is complete to the bark edge, then when dated a precise date of felling can be determined. The felling date will be precise to the season of the year, depending on the degree of formation of the outermost ring. Therefore, a tree with bark which has the spring vessels formed but no summer growth can be said to be felled in the spring, although it is not possible to say in which particular month the tree was felled.
Section of tree with conversion methods showing three types of sapwood retention resulting in A terminus post quem, B a felling date range, and C a precise felling date. Enlarged area D shows the outermost rings of the sapwood with growing seasons (Miles 1997, 42)
Another important dimension to dendrochronological studies is the presence of sapwood. This is the band of growth rings immediately beneath the bark and comprises the living growth rings which transport the sap from the roots to the leaves. This sapwood band is distinguished from the heartwood by the prominent features of colour change and the blocking of the spring vessels with tyloses, the waste products of the tree’s growth. The heartwood is generally darker in colour, and the spring vessels are blocked with tyloses. The heartwood is dead tissue, whereas the sapwood is living, although the only really living, growing, cells are in the cambium, immediately beneath the bark. In European oak (Quercus robur sp), the difference in colour is generally matched by the change in the spring vessels. Generally the sapwood retains stored food and is therefore attractive to insect and fungal attack once the tree is felled and therefore is often removed during conversion.
Sapwood in European oaks tends to be of a relatively constant width and/or number of rings. By determining what this range is with an empirically or statistically-derived estimate is a valuable aspect in the interpretation of tree-ring dates where the bark edge is not present (Miles 1997). The narrower this range of sapwood rings, the more precise the estimated felling date range will be.
Methodology: The Dating Process
All timbers sampled were of oak (Quercus spp.) from what appeared to be primary first-use timbers, or any timbers which might have been re-used from an early phase. Those timbers which looked most suitable for dendrochronological purposes with complete sapwood or reasonably long ring sequences were selected. In situ timbers were sampled through coring, using a 16mm hollow auger. Details and locations of the samples are detailed in the summary table.
The dry samples were sanded on a linisher, or bench-mounted belt sander, using 60 to 1200 grit abrasive paper, and were cleaned with compressed air to allow the ring boundaries to be clearly distinguished. They were then measured under a x10/x30 microscope using a travelling stage electronically displaying displacement to a precision of 0.01mm. Thus each ring or year is represented by its measurement which is arranged as a series of ring-width indices within a data set, with the earliest ring being placed at the beginning of the series, and the latest or outermost ring concluding the data set.
The principle behind tree-ring dating is a simple one: the seasonal variations in climate-induced growth as reflected in the varying width of a series of measured annual rings is compared with other, previously dated ring sequences to allow precise dates to be ascribed to each ring. When an undated sample or site sequence is compared against a dated sequence, known as a reference chronology, an indication of how good the match is must be determined. Although it is almost impossible to define a visual match, computer comparisons can be accurately quantified. Whilst it may not be the best statistical indicator, Student’s (a pseudonym for W S Gosset) t-value has been widely used amongst British dendrochronologists. The cross-correlation algorithms most commonly used and published are derived from Baillie and Pilcher’s CROS programme (Baillie and Pilcher 1973), although a faster version (Munro 1984) giving slightly different t-values is sometimes used for indicative purposes.
Generally, t-values over 3.5 should be considered to be significant, although in reality it is common to find demonstrably spurious t-values of 4 and 5 because more than one matching position is indicated. For this reason, dendrochronologists prefer to see some t-value ranges of 5, 6, or higher, and for these to be well replicated from different, independent chronologies with local and regional chronologies well represented. Users of dates also need to assess their validity critically. They should not have great faith in a date supported by a handful of t-values of 3’s with one or two 4’s, nor should they be entirely satisfied with a single high match of 5 or 6. Examples of spurious t-values in excess of 7 have been noted, so it is essential that matches with reference chronologies be well replicated, and that this is confirmed with visual matches between the two graphs. Matches with t-values of 10 or more between individual sequences usually signify having originated from the same parent tree.
In reality, the probability of a particular date being valid is itself a statistical measure depending on the t-values. Consideration must also be given to the length of the sequence being dated as well as those of the reference chronologies. A sample with 30 or 40 years growth is likely to match with high t-values at varying positions, whereas a sample with 100 consecutive rings is much more likely to match significantly at only one unique position. Samples with ring counts as low as 50 may occasionally be dated, but only if the matches are very strong, clear and well replicated, with no other significant matching positions. This is essential for intra-site matching when dealing with such short sequences. Consideration should also be given to evaluating the reference chronology against which the samples have been matched: those with well-replicated components which are geographically near to the sampling site are given more weight than an individual site or sample from the opposite end of the country.
It is general practice to cross-match samples from within the same phase to each other first, combining them into a site master, before comparing with the reference chronologies. This has the advantage of averaging out the ‘noise’ of individual trees and is much more likely to obtain higher t-values and stronger visual matches. After measurement, the ring-width series for each sample is plotted as a graph of width against year on log-linear graph paper. The graphs of each of the samples in the phase under study are then compared visually at the positions indicated by the computer matching and, if found satisfactory and consistent, are averaged to form a mean curve for the site or phase. This mean curve and any unmatched individual sequences are compared against dated reference chronologies to obtain an absolute calendar date for each sequence. Sometimes, especially in urban situations, timbers may have come from different sources and fail to match each other, thus making the compilation of a site master difficult. In this situation samples must then be compared individually with the reference chronologies.
Therefore, when cross-matching samples with each other or against reference chronologies, a combination of both visual matching and a process of qualified statistical comparison by computer is used. The ring-width series were compared on an IBM compatible computer for statistical cross-matching using a variant of the Belfast CROS program (Baillie and Pilcher 1973). A version of this and other programmes were written in BASIC by D Haddon-Reece, and re-written in Microsoft Visual Basic by M R Allwright and P A Parker.
Ascribing and Interpreting Felling Dates
Once a tree-ring sequence has been firmly dated in time, a felling date, or date range, is ascribed where possible. For samples which have sapwood complete to the underside of, or including bark, this process is relatively straight forward. Depending on the completeness of the final ring, i.e. if it has only the early wood formed, or the latewood, a precise felling date and season can be given. If the sapwood is partially missing, or if only a heartwood/sapwood transition boundary survives, then an estimated felling date range can be given for each sample. The number of sapwood rings can be estimated by using a statistically derived sapwood estimate with a given confidence limit. A review of the geographical distribution of dated sapwood data from historic building timbers has shown that a 95% range of 9-41 rings is most appropriate for the southern counties of England (Miles 1997), which will be used here. If no sapwood or heartwood/sapwood boundary survives, then the minimum number of sapwood rings from the appropriate sapwood estimate is added to the last measured ring to give a terminus post quem (tpq) or felled after date.
An alternative method of estimating felling date ranges has recently been developed (Miles 2005) which runs as a function under OxCal (Bronk Ramsey 1995; Miles and Bronk Ramsey in prep). Instead of using a simple empirical estimate for a particular geographical location, one model was found to be suitable for the whole of England and Wales. With the methodology set out by Millard (2002), Bayesian statistical models are used to produce individual sapwood estimates for samples using the variables of number of heartwood rings present, the mean ring width of those heartwood rings, the heartwood/sapwood boundary date, and the number of any surviving sapwood rings or a count of those lost in sampling. Using the suite of calculation and graphical plotting functions in OxCalInput and OxCalPlot (Bronk Ramsey in prep), the area of highest probability density for each sample can be graphically displayed to any of three confidence levels. The addition of surviving sapwood to the equation narrows the felling date range for each sample, although the outer end of the range shifts slightly later, more noticeably on those samples with higher sapwood counts. An empirically-derived stock-piling factor added to the ranges produced also helps to make the estimated felling date ranges more representative for the actual latest common felling date, from which a construction date can then be extrapolated.
This new method of predicting sapwood ranges has resulted in over 94% of the samples tested producing felling date ranges narrower than the 36-year empirical estimate currently used. About a quarter of the samples tested showed an improvement with a range of 24 years or less. Conversely, some 4.5% of the samples tested produced a range larger than the empirical range, but again these ranges are more representative of the actual sapwood found.
However, it has been found that some unusual samples do not fit the model well. These include samples which have exceptional or sudden variation in mean ring width, such as might be found in pollarded or managed timber. Sometimes a tree will exhibit a sudden drop in mean ring width toward the end of its life, resulting in more sapwood rings being present then might be suggested in the faster-grown heartwood. Additionally, samples which have come from small timbers converted from larger, slow-grown trees would have a much larger number of heartwood rings then were actually present in the sample. Some examples of heartwood ring counts of 25 years or less with a narrow mean ring width are good indicators of this situation, as were observations made during sampling. Samples with these characteristics should be excluded from such analysis.
A particularly useful feature of OxCalPlot is the ability of producing combined felling date ranges for a group of samples comprising a single phase of building. Here, two samples combined can reduce the individual felling date ranges from about 30 to about 20 years. By including more samples within the combined phase, this 20-year range can be reduced to half or even less, depending on the number of samples in the phase. Thus felling date ranges for combined building phases have the potential to being reduced by as much as a two-thirds or even three-quarters of the individual empirically-derived felling date ranges (Miles 2005).
Some caution must be used in interpreting solitary precise felling dates. Many instances have been noted where timbers used in the same structural phase have been felled one, two, or more years apart. Whenever possible, a group of precise felling dates should be used as a more reliable indication of the construction period. It must be emphasised that dendrochronology can only date when a tree has been felled, not when the timber was used to construct the structure under study. However, it is common practice to build timber-framed structures with green or unseasoned timber and that construction usually took place within twelve months of felling (Miles 2006).
Details of Dendrochronological Analysis
The results of the dendrochronological analysis for the building under study are presented in a number of detailed tables. The most useful of these is the summary Table 1. This gives most of the salient results of the dendrochronological process, and includes details for each sample, its location, and its felling date or date range, if successfully tree-ring dated. This last column is of particular interest to the end user, as it gives the actual year and season when the tree was felled, if bark is present, or an estimated felling date range if the sapwood is incomplete. Occasionally it will be noted that the felling date ranges may not coincide with the precise felling dates. This is nothing to be overly concerned about so long as these are not too far apart. It must be remembered that the estimated felling date ranges are calculated at a 95% confidence level, which means that statistically one sample in 20 will have felling dates which actually fall outside the predicted range.
It will also be noticed that often the precise felling dates will vary within several years of each other. Unless there is supporting archaeological evidence suggesting different phases, all this would indicate is either stockpiling of timber, or of trees which have been felled or died at varying times but not cut up until the commencement of the particular building operations in question. When presented with varying precise felling dates, one should always take the latest date for the structure under study, and it is likely that construction will have been completed for ordinary vernacular buildings within twelve or eighteen months from this latest felling date (Miles 1997).
Table 2 gives an indication of the statistical reliability of the match between one sequence and another. This shows the t-value over the number of years overlap for each combination of samples in a matrix table. It should be born in mind that t-values with less than 80 rings overlap may not truly reflect the same degree of match and that spurious matches may produce similar values.
First, multiple radii have been cross-matched with each other and combined to form same-timber means. These are then compared with other samples from the site and any which are found to have originated from the same parent tree are again similarly combined. Finally, all samples, including all same timber and same tree means are combined to form one or more site masters. Again, the cross-matching is shown as a matrix table of t-values over the number of years overlaps. Reference should always be made to Table 1 to clearly identify which components have been combined.
Table 3 shows the degree of cross-matching between the site master(s) with a selection of reference chronologies. This shows the county or region from which the reference chronology originated, the common chronology name together with who compiled the chronology with publication reference and the years covered by the reference chronology. The years overlap of the reference chronology and the site master being compared are also shown together with the resulting t-value. It should be appreciated that well replicated regional reference chronologies, which are shown in bold, will often produce better matches than with individual site masters or indeed individual sample sequences.
Figures include a bar diagram which shows the chronological relationship between two or more dated samples from a phase of building. The site sample record sheets are also appended, together with any plans showing sample locations, if available.
Publication of all dated sites are published in Vernacular Architecture annually, and the entry, if available, is shown on the summary page of the report. This does not give as much technical data for the samples dated, but does give the t-value matches against the relevant chronologies, provide a short descriptive paragraph for each building or phase dated, and gives a useful short summary of samples dated. These summaries are also listed on the web-site maintained by the Laboratory, which can be accessed at www.dendrochronology.com. The Oxford Dendrochronology Laboratory retains copyright of this report, but the commissioner of the report has the right to use the report for his/her own use so long as the authorship is quoted. Primary data and the resulting site master(s) used in the analysis are available from the Laboratory on request by the commissioner and bona fide researchers. The samples form part of the Laboratory archives.
Summary of Dating
The dendrochronology was commissioned to allow an accurate chronology of building to be determined for the building. Whilst the parlour wing had an inscribed date of 1616, the hall range and the east range were much more difficult to interpret.
Therefore a limited sampling programme was undertaken with samples taken from five timbers in the east range, and five timbers from the hall range. There were a number of confusing elements in the hall, with what might look like an inserted ceiling, a large beam adjacent which might have related to a screens passage, and the roof structure.
Multiple samples were taken from three timbers to enable a good ring sequence to be obtained and to allow retention of the sapwood complete to the bark edge. After comparing and averaging together these multiple radii, the same-timber means owl1 and owl11 were constructed for the south-west lower purlin of the east range and the large hall ceiling beam respectively. These means were then used in the subsequent analysis. A secondary core from a ceiling beam in the east range (owl5b) failed to match the main core owl5a conclusively.
Three timbers from the east range were found to match each other. However, as the cross-matching between the samples was not exceptional, the matches were confirmed by independent cross-matching with the reference chronologies. Similarly, four samples from the hall range were found to match, and all seven timbers were combined to form the 162-year site master OWLPEN. This was compared with the reference chronologies and was found to date conclusively, spanning the years 1424-1585. One other timber, the south-west lower purlin from the east range (owl1), dated individually to 1196-1285, suggesting that this timber was reused from another now-demolished structure. Two other timbers failed to date, either on account of there being too few rings (owl3) or having areas of distressed, distorted ring sequences (owl13).
One of the timbers from the east range, the intermediate ceiling beam owl5a, had bark edge, and therefore produced a precise felling date of spring 1539. Two collars, owl2 and owl4, only retained their heartwood/sapwood boundaries, but the felling date ranges of 1520-52 and 1529-61 respectively were both consistent with the 1539 felling date produced by owl5a. Thus this range is likely to have been constructed in 1539 or within a year or two after this date. The south-west lower purlin owl1 produced a felling date range of 1294-1326 and this timber can only have been reused, either inserted later, or more likely incorporated at the time of construction around 1539.
The results from the hall range are much less straightforward. The earliest date is for one of the common joists to the hall ceiling (owl12), giving a felling date range of 1514-38. This might just possibly be of the same construction phase as a collar from the truss immediately adjacent to the east range (owl15), having been felled in the summer or autumn of 1541. A later phase is identified through the large beam visible in the hall (owl11), which was felled in the spring of 1584, and the valley rafter to the large gable above (owl14) felled in the spring of 1586. It is likely that both of these relate to a later phase of alterations to provide additional accommodation above the hall range, which probably commenced in 1586 or shortly thereafter.
Acknowledgements
The dating was commissioned by Sir Nicholas Mander and co-ordinated by Dr Nat Alcock who assisted with the sampling and provided the architectural analysis used in this report. Michael Worthington assisted in the laboratory and Dr Martin Bridge prepared the bar diagram. Thanks are also given to other laboratories for access to local reference chronologies.
References
Arnold, A J, Howard, R E, and Litton, C D, 2004 Tree-ring analysis of timbers from New Inn House, 7 Wotton Road, Kingswood, Gloucestershire, Centre for Archaeol Rep, 62/2004
Arnold, A J, Howard, R, and Litton, C D, 2006 Tree-ring analysis of timbers from Kingsbury Hall, Kingsbury, Warwickshire, Res Dept Rep, 53/2006
Baillie, M G L, and Pilcher, J R, 1973 A simple cross-dating program for tree-ring research, Tree-Ring Bulletin, 33, 7-14
Bronk Ramsey, C, 1995 Radiocarbon calibration and stratigraphy: the OxCal program, Radiocarbon, 37, 425-30
Haddon-Reece, D, and Miles, D H, 1993 Working compilation of 190 British reference chronologies supplied by various researchers, unpubl computer file MASTERAL, Oxford Dendrochronology Laboratory
Miles, D H, 1997 The interpretation, presentation, and use of tree-ring dates, Vernacular Architecture, 28, 40-56
Miles, D H, 1997b Working compilation of 58 reference chronologies centred around Wales by various researchers, unpubl computer file WALES97, Oxford Dendrochronology Laboratory
Miles, D H, 1997c Working compilation of 55 reference chronologies centred around Hampshire by various researchers, unpubl computer file HANTS97, Oxford Dendrochronology Laboratory
Miles, D W H, 2001 Tree-Ring Dating of Court Farm Barn, Church Lane, Winterbourne, Gloucestershire, Centre for Archaeol Rep, 34/2001
Miles, D, 2003 Dating Buildings and Dendrochronology in Hampshire, in Hampshire Houses 1250 - 1700: Their Dating and Development (ed E Roberts), 220-6, Southampton (Hampshire County Council)
Miles, D H, 2004 Working compilation of reference chronologies centred around Somerset by various researchers, unpubl computer file SOMRST04, Oxford Dendrochronology Laboratory
Miles, D H, 2005 New Developments in the Interpretation of Dendrochronology as Applied to Oak Building Timbers, Unpubl DPhil thesis, Hertford College, Oxford Univ
Miles, D H, 2006 Refinements in the Interpretation of Tree-Ring Dates for Oak Building Timbers in England and Wales, Vernacular Architecture, 37, 84-96
Miles, D H, Worthington, M J, and Bridge, M C, 2007 Tree-ring dates, Vernacular Architect, 38, 120-139
Millard, A, 2002 A Bayesian approach to sapwood estimates and felling dates in dendrochronology, Archaeometry, 44 (1), 137-143
Munro, M A R, 1984 An Improved Algorithm for Crossdating Tree-Ring Series, Tree Ring Bulletin, 44, 17-27
Tyers, I, 2002 Tree-ring analysis of oak timbers from the Abbot's Hall and Parlour at Wigmore Abbey, near Adforton, Herefordshire, Centre for Archaeol Rep, 112/2002
Tyers, I, 2006 Dendrochronological of the Doom Panel, Church of St James the Great, Dauntsey, Wiltshire, Res Rep Ser, 44/2006
Table 1: Summary of Tree-Ring Dating
OWLPEN MANOR, OWLPEN, DURSLEY, GLOUCESTERSHIRE
Sample Timber and position Dates AD H/S Sapwood No of Mean Std Mean Felling seasons and
number & type spanning bdry complement rings width devn sens dates/date ranges (AD)
mm mm mm
Unit A (East Range)
owl1a c South-west lower purlin (reused) bay AI-II 1211-1278 68 1.83 0.55 0.205
owl1b c ditto 1196-1285 1285 H/S 90 1.38 0.58 0.253
owl1c c ditto 1242-1285 44 1.25 0.37 0.206
owl1 Mean of owl1a + owl1b + owl1c 1196-1285 1285 H/S 90 1.58 0.54 0.208 1294-1326
* owl2 c Collar T-AII 1440-1513 1511 2 74 2.07 0.67 0.202 1520-52
owl3 c Rafter - 9 39 2.80 1.15 0.269
* owl4 c Collar T-AIIII 1454-1520 1520 H/S 67 1.46 0.71 0.217 1529-61
* owl5a c Intermediate 1st floor ceiling beam AIII-IIII 1456-1538 1518 20¼C 83 2.64 1.29 0.196 Spring 1539
owl5b c ditto - +16 16 2.60 0.55 0.138
Hall Range
owl11a1 c Ceiling beam 1424-1459 36 0.90 0.38 0.287
owl11a2 c ditto 1462-1542 81 1.36 0.34 0.180
owl11b c ditto 1424-1583 1559 24¼C 160 1.24 0.49 0.242
*owl11 Mean of owl11a1 + owl11a2 + owl11b 1424-1583 1559 24¼C 160 1.26 0.41 0.213 Spring 1584
*owl12 c North ceiling joist centre east panel 1468-1513 1497 16 46 2.77 1.67 0.265 1514-38
owl13 c South principal rafter T-BIII - 30C 56 0.71 0.19 0.200
*owl14 c South-west central valley rafter 1522-1585 20¼C 64 1.49 0.57 0.179 Spring 1586
owl15a c Collar T-BI - 50 1.49 0.60 0.212
*owl15b c ditto 1478-1540 19½C 63 1.38 0.34 0.181 Summer 1541
* = OWLPEN Site Master 1424-1585 162 1.64 0.56 0.173
Key: *, †, § = sample included in site-master; c = core; mc = micro-core; s = slice/section; g = graticule; p = photograph; ¼C, ½C, C = bark edge present, partial or complete ring:
¼C = spring (last partial ring not measured), ½C = summer/autumn (last partial ring not measured), or C = winter felling (ring measured); H/S bdry = heartwood/sapwood
boundary - last heartwood ring date; std devn = standard deviation; mean sens = mean sensitivity
Explanation of terms used in Table 1
The summary table gives most of the salient results of the dendrochronological process. For ease in quickly referring to various types of information, these have all been presented in Table 1. The information includes the following categories:
Sample number: Generally, each site is given a two or three letter identifying prefix code, after which each timber is given an individual number. If a timber is sampled twice, or if two timbers were noted at time of sampling as having clearly originated from the same tree, then they are given suffixes ‘a’, ‘b’, etc. Where a core sample has broken, with no clear overlap between segments, these are differentiated by a further suffix ‘1’, ‘2’, etc.
Type shows whether the sample was from a core ‘c’, or a section or slice from a timber‘s’. Sometimes photographs are used ‘p’, or timbers measured in situ with a graticule ‘g’.
Timber and positioncolumn details each timber sampled along with a location reference. This will usually refer to a bay or truss number, or relate to compass points or to a reference drawing.
Dates AD spanning gives the first and last measured ring dates of the sequence (if dated),
H/S bdryis the date of the heartwood/sapwood transition or boundary (if present). This date is critical in determining an estimated felling date range if the sapwood is not complete to the bark edge.
Sapwood complement gives the number of sapwood rings. The tree starts growing in the spring during which time the earlywood is produced, also known also as spring growth. This consists of between one and three decreasing spring vessels and is noted as Spring felling and is indicated by a ¼ C after the number of sapwood ring count. Sometimes this can be more accurately pin-pointed to very early spring when just a few spring vessels are visible. After the spring growing season, the latewood or summer growth commences, and is differentiated from the proceeding spring growth by the dense band of tissue. This summer growth continues until just before the leaves drop, in about October. Trees felled during this period are noted as summer felled (½ C), but it is difficult to be too precise, as the width of the latewood can be variable, and it can be difficult to distinguish whether a tree stopped growing in autumn or winter. When the summer growth band is clearly complete, then the tree would have been felled during the dormant winter period, as shown by a single C. Sometimes a sample will clearly have complete sapwood, but due either to slight abrasion at the point of coring, or extremely narrow growth rings, it is impossible to determine the season of felling.
Number of rings: The total number of measured rings present on the samples analysed.
Mean ring width: This, simply put, is the sum total of all the individual ring widths, divided by the number of rings, giving an average ring width for the series.
Mean sensitivity: A statistic measuring the mean percentage, or relative, change from each measured yearly ring value to the next; that is, the average relative difference from one ring width to the next, calculated by dividing the absolute value of the differences between each pair of measurements by the average of the paired measurements, then averaging the quotients for all pairs in the tree-ring series (Fritts 1976). Sensitivity is a dendrochronological term referring to the presence of ring-width variability in the radial direction within a tree which indicates the growth response of a particular tree is “sensitive” to variations in climate, as opposed to complacency.
Standard deviation: The mean scatter of a population of numbers from the population mean. The square root of the variance, which is itself the square of the mean scatter of a statistical population of numbers from the population mean. (Fritts 1976).
Felling seasons and dates/date ranges is probably the most important column of the summary table. Here the actual felling dates and seasons are given for each dated sample (if complete sapwood is present). Sometimes it will be noticed that often the precise felling dates will vary within several years of each other. Unless there is supporting archaeological evidence suggesting different phases, all this would indicate is either stockpiling of timber, or of trees which have been felled or died at varying times but not cut up until the commencement of the particular building operations in question. When presented with varying precise felling dates, one should always take the latest date for the structure under study, and it is likely that construction will have been completed for ordinary vernacular buildings within twelve or eighteen months from this latest felling date (Miles 2006).
Felling date ranges are produced using an empirical estimates using the appropriate estimate (Miles 1997). However, these can sometimes be reduced using a new sapwood estimation methodology which uses the mean ring width, number of heartwood rings, known H/S boundary date, and the number of surviving sapwood rings, if present (Miles 2006). These are used after the empirical range and are shown in brackets (OxCal followed by date range). Combined felling date ranges for a phase of building is shown at the end of the phase to which it relates.
Table 2: Matrix of t-values and overlaps for same-timber means and site masters
Components of timber owl1 Components of timber owl11
Sample: |
owl1b |
owl1c |
|
|
Sample: |
owl11a2 |
owl11b |
Last ring date AD: |
1285 |
1285 |
|
|
Last ring date AD: |
1542 |
1583 |
|
|
|
|
|
|
|
|
owl1a |
3.24 |
6.06 |
|
|
owl11a1 |
0.00 |
4.31 |
|
68 |
37 |
|
|
|
0 |
36 |
|
|
|
|
|
|
|
|
|
owl1b |
12.71 |
|
|
|
owl11a2 |
9.49 |
|
|
44 |
|
|
|
|
81 |
Components of site master OWLPEN
Sample: |
owl4 |
owl5a |
owl11 |
owl12 |
owl14 |
owl15b |
Last ring date AD: |
1520 |
1538 |
1583 |
1513 |
1585 |
1540 |
|
|
|
|
|
|
|
owl2 |
6.44 |
2.06 |
3.85 |
1.91 |
0.00 |
1.08 |
|
60 |
58 |
74 |
46 |
0 |
36 |
|
|
|
|
|
|
|
|
owl4 |
1.75 |
3.35 |
1.91 |
0.00 |
0.77 |
|
|
65 |
67 |
46 |
0 |
43 |
|
|
|
|
|
|
|
|
|
owl5a |
3.70 |
1.73 |
0.00 |
1.48 |
|
|
|
83 |
46 |
17 |
61 |
|
|
|
|
|
|
|
|
|
|
owl11 |
4.60 |
3.78 |
4.77 |
|
|
|
|
46 |
62 |
63 |
|
|
|
|
|
|
|
|
|
|
|
owl12 |
0.00 |
2.29 |
|
|
|
|
|
0 |
36 |
|
|
|
|
|
|
|
|
|
|
|
|
owl14 |
0.28 |
|
|
|
|
|
|
19 |
|
|
|
|
|
|
|
Table 3a: Dating of timber owl1 (1196-1285) against reference chronologies at 1285
|
County or region: |
Chronology name: |
Short publication reference: |
File name: |
Spanning: |
Overlap: |
t-value: |
|
Gloucestershire |
New Inn House |
(Arnold, Howard, and Litton 2004) |
KGWBSQ01 |
1191-1519 |
90 |
8.59 |
|
Gloucestershire |
Winterborne Tithe Barn |
(Miles 2001) |
WNTERBRN |
1177-1341 |
90 |
6.77 |
|
Gloucestershire |
Old Manse, Wotton-Under-Edge |
(Miles et al 2005) |
omw5 |
1193-1320 |
90 |
6.29 |
|
Wales |
Welsh Master Chronology |
(Miles 1997) |
WALES97 |
404-1981 |
90 |
6.04 |
|
Wiltshire |
Doom Panel, St James Church |
(Tyers 2006) |
DAUNTSEY |
1154-1349 |
90 |
5.74 |
|
Herefordshire |
Wigmore Abbey |
(Tyers 2002) |
WIGALL46 |
1055-1729 |
90 |
5.62 |
|
Somerset |
Somerset Master Chronology |
(Miles 2004) |
SOMRST04 |
770-1979 |
90 |
5.39 |
Table 3b: Dating of site master OWLPEN (1424-1585) against reference chronologies at 1585
|
County or region: |
Chronology name: |
Short publication reference: |
File name: |
Spanning: |
Overlap: |
t-value: |
|
Great Britain |
British Isles Master Chronology |
(Haddon-Reece and Miles 1993) |
MASTERAL |
404-1987 |
162 |
10.21 |
|
Hampshire |
Hampshire Master Chronology |
(Miles 2003) |
HANTS02 |
443-1972 |
162 |
9.94 |
|
Shropshire |
Shropshire Master Chronology |
(Miles 1995) |
SALOP95 |
881-1745 |
162 |
8.76 |
|
Somerset |
Somerset Master Chronology |
(Miles 2004) |
SOMRST04 |
770-1979 |
162 |
8.71 |
|
Wales |
Welsh Master Chronology |
(Miles 1997) |
WALES97 |
404-1981 |
162 |
8.67 |
|
Warwickshire |
Kingsbury Hall |
(Arnold et al 2006) |
KNGHSQ01 |
1391-1564 |
141 |
8.37 |
|
Hampshire |
St Michael's Cottage, Chilbolton |
(Miles et al 2007) |
CHLBLTN1 |
1421-1554 |
131 |
8.32 |
|
