Dendrochronology is the leading scientific method for establishing when a piece of timber was felled — and, in turn, helping to date the construction or alteration of historic buildings. By analysing the pattern of annual growth rings (which vary according to climate), samples taken from a building can be compared against vast regional databases to identify precise felling dates. Together with isotopic analysis, it is the most accurate dating technique currently available.

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Sampling must be undertaken with great care. Ideally, a radial core — from pith to bark — is extracted without damaging the integrity of the timber or the structure. This is carried out using specialist coring equipment and strictly in line with English Heritage Dendrochronology Guidelines. The best results are obtained from oak samples with a sound bark edge, minimal distortion, and at least 100 growth rings — although such timbers can be difficult to locate.

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Recent work includes the remarkable fourteenth-century Upper Library at Merton College, Oxford, where coring revealed the oak panelling was installed in two distinct phases: English/Welsh oak felled between 1598–1628 and northern Baltic imports dating from 1637–1655.

Other examples include:

• Nullis Farm, Spencers Wood, Berkshire — farmhouse timbers dated to 1558 (bark edge present)

• Great Barn, Lewknor — precise felling dates recorded between winter 1342/3 and spring 1344

• Long-term sampling programmes at the Tower of London, Westminster Hall & Abbey, Hampton Court Palace, Windsor Castle, and Salisbury Cathedral, where almost 700 samples have been collected over the past 25 years.

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Further information, including likely costs, can be obtained by contacting Daniel Miles via our contact page.

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