Tree rings save a piece of past

English Heritage has stepped in to save Britain's oldest timber-framed shop, thanks to specialist dating work carried out by a researcher at University College London.

The 13th-century structure was uncovered when local builders began work on what was presumed to be a Victorian property, a former chemist's shop, at 173 Berkhamsted High Street in Hertfordshire.

The local council recognised the potential importance of the discovery and called in Martin Bridge from UCL's archaeology department. Dr Bridge, who has also worked on the Tudor warship the Mary Rose, is an expert in tree-ring dating.

Dendrochronological testing is a statistical method of assessing the age of timber by looking at the pattern of tree-ring widths in the wood. It relies on the theory that the same species will show the same pattern of growth in relation to the weather.

Dr Bridge attempted to match the shop's timber patterns against a dataset going back about 2,000 years.

He said the process was complicated by the fact that the sapwood on the outside of the tree had clearly been chopped off when the timbers were originally used. This made it impossible for Dr Bridge to give a precise date. But based on a trace of the sapwood he was able to make "an educated statistical estimate" that the structure was built between 17 and 1297.

Following this affirmation of the building's great age, English Heritage has announced a £250,000 grant towards repairs to the shop.

Specialist carpenters and craftsmen will re-work parts of the walls, preserving timbers and beams, as well as retaining and repairing the roof structure. Work will also be carried out to protect a recently unearthed historic well on the premises.

The shop will open with special public access in autumn next year.