From the Thorley Archives

The Dendrochronological Dating of the St Barnabas Barn

This article has been written as a tribute to Adrian Gibson M.B.E. who died suddenly on March 16th 2006. It was a privilege to know Adrian Gibson as a friend and as an authority with a national reputation for the study of medieval timber-framed buildings. Fittingly Adrian's funeral took place in a packed St. Barnabas Centre on March 27th. Much of the research on our barn website was either undertaken or prompted by Adrian. He was most generous with his time, enthusiasm and knowledge.

Adrian holding two core samples


Dendrochronology, or tree ring dating, provides an indication of when a timber-framed building was constructed, through an assessment of the growth ring patterns in a cross-section of the trunks of the timbers used. Variations in the thickness of the annual growth rings give a unique pattern for each tree species within a particular geographical region. Unique core sample configurations may be likened to a product bar code. A year with favourable growing conditions will produce a wider growth ring than a year with poor growing conditions. By cross matching a core sample of a timber from an existing historic building with a master or reference chronology database (of say, oak trees in East Anglia), scientists are able to determine when the timber was felled. If the section of timber still retains its bark, this can be used to determine the year and even the season that the tree was felled. Historically, oak timber was trimmed and shaped for construction purposes within a year of felling as the oak became harder to work after twelve months. The accepted construction timetable for a timber-framed building was to fell the timber in the Winter, shape and form the timbers in the Spring, erect the building in the Summer ready for 'fitting out' and occupation in the Autumn.

Each ring represents a year's growth
- good years give wide rings

Ancient barns can usually be dated according to such features as styles of roof construction, the timber bracing of the walls and the joints used to peg the timbers together. Our St. Barnabas barn underwent many minor modifications throughout its approximate 450 year old history due to 'wear and tear'. Adrian was curious to know the original construction date as the present configuration of the side aisles didn't match the older joints which join the long lengths in the roof timbers. He persuaded English Heritage to undertake a 'dendro' dating exercise to resolve his hypothesis that the barn was in fact much older than its present style suggests. Andy Moir (Tree Ring Services) was commissioned to carry out the work in November 2003.

Taking a core from a beam with original bark in the office
Extracting the oak core sample from the hollow drill

Under Adrian's guidance twelve core samples were taken from various significant timbers around our barn. English Heritage recommends that 50 rings should be present in each sample and that a minimum of eight to ten samples are taken from any one building. Back in his laboratory Andy then prepared the 10mm cores for analysis by squaring and polishing each one. The dimensions of each ring are measured and the results recorded on both a graph and on a computer for statistical analysis. Our samples were then compared on a database with other master chronologies of East Anglian oak trees spanning hundreds of years.

Examples of cores prepared for analysis

In April this year English Heritage released the results of their analysis of the twelve core samples. Nine cores gave an accurate and consistent date for the primary building phase of the barn. Assuming that the construction took place shortly after the winter felling of the oak trees, our barn was constructed in 1531. The oldest oak tree used to build the barn started life as a seedling in about 1350!

Other historic events that happened in 1531

* The Leventhorpe family were owners of Thorley Hall Farm
* Parliament makes Henry VIII head of the Church of England
* Copernicus shows the earth revolves around the sun
* William Shakespeare's father John was born

From the interim results Adrian Gibson's theory as to the probable date for the original building of the St Barnabas barn has proved to be correct. Fortunately English Heritage had privately divulged to Adrian the date of the barn some time before his death.

Bill Hardy
May 2006

From the Archives