Dating the timbers of Bishops' House

Most of the timber buildings in England were built from oak. Each year an oak tree grows a new layer of wood under the bark. The thickness of that layer – the tree ring – depends largely on what the climate has been like during the growing season – usually from March to September. Because nature never gives us the same run of wet, dry, warm and cold growing seasons, so the width of the growth rings never repeats itself and a technique, called dendrochronology, can be used to accurately date timber buildings going back many centuries.

A first attempt to date Bishops’ House was made in 1977 and you can see some of the samples used, in the Tapestry Room at the East end of the building. But that attempt never gave an absolute date for the timber building. Tree ring dating techniques have improved over the last forty years so in 2017 the Friends of Bishops’ House obtained permission from Sheffield City Council to take a new set of samples. The Nottingham Tree Ring Dating Laboratory was able to use 14 samples from around the House to date the building. They drilled into the main beams and extracted a core of wood about the size of a pencil, and counted the rings, matching them against samples of known date.

When the Friends of Bishops’ House took over running the building and began to study it and investigate its history, we had been told that the larger part of the building, containing the Hall, was the earliest, dating to around 1500 from the style of its construction and from its associations with the Blythe family. We were told that the cross range, including the Parlour had been added about fifty years later. This was based on an early interpretation of the building, and from the first attempt at dendrochronology. So, when we got the results from the 2017 sampling, they were quite a surprise.

The results showed that the part of the House which includes the Parlour were the oldest part of the building. The trees were felled in 1553 so the House would have been put up the year after, in 1554. The date for the part including the Hall was 1579 so it would have been built in 1580. This has completely turned around our interpretation of the building. Unfortunately the samples can’t tell us which area of woodland the trees were felled from.

The 1977 report was inconclusive on the source of the original beams, citing the possibility that while a likely source would have been the nearby Sherwood Forest, a good match for the tree rings came from the West Midlands. The report mentioned that the prosperity of the occupants as a result of the scythe-manufacturing industry in Sheffield may have allowed them to be more selective in sourcing the timber, and that there are many records as far back as the twelfth century on the movement of oak planks over great distances.

The 2017 report was also unable to pin down the source of the timbers, concluding that the cored samples matched reference collections from different parts of England such as Warwickshire, Cheshire, Derbyshire and Yorkshire equally well. The samples from this report have borne out one additional piece of information, however. It appears that some of the samples from both parts of the building match each other so closely that each group would have come from adjacent trees in the same patch of woodland.

The dated samples from each of the two phases of the timber framed building also corresponded so closely that it also appears that they were all felled at the same time. The earliest rings from deep within the sampled cores are from 1399 for the Phase One building and 1442 for the Phase Two building. Both these dates show us that the woodland sources chosen had stands of mature oak trees.

Our thanks to Alison Arnold and Robert Howard of the Nottingham Tree Ring Dating Laboratory.

Fig 1 One of the core samples photographed just after being removed. You can just see the tree rings in the close-up below.

Fig 3 Robert Howard drilling into one of the timber posts in the room above the Parlour.

 

Fig 4 Alison Arnold working at the east end of Bishops’ House.

 

Sources

Arnold A and Howard R (2017) Bishops’ House Norton Lees Lane, Norton Lees, Sheffield. Tree-Ring analysis of timbers. The Nottingham tree-ring dating laboratory.

Morgan R (1977) Dendrochronological dating of a Yorkshire timber building. Vernacular Architecture 8, 809-814.

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