Building Bishops' House

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Using Oak

In the sixteenth century timber was the main construction material for buildings in England, though stone was of course used where it was readily available and where it could be afforded. The sixteenth century saw England change from a small backwater country to a major European trading nation. With the rise in wealth came the demand for more elaborate buildings and Bishops’ House, in its modest way, reflects part of this change. The forests of England which for centuries had provided an inexhaustible supply of timber began, for the first time to be depleted, not only with the demand for domestic architecture, but also the demands of an increasingly large navy and merchant fleet.

Nonetheless, timber framed buildings were still the dominant form of building across the country until well into the 17^th century when there was a great spread in the use of bricks, especially after the Reformation of 1660. The reason for this was the expense of utilising other forms of construction. There were few permanent quarries with most local ones being opened for a single major project. Brick and stone masons tended to congregate around major cities and their costs were prohibitive, even for the relatively wealthy.

Over 90% of timber-framed buildings were made of oak. This figure is not just an accident of survival as other species are preserved as well. Historical records show that oak was both the most expensive and the most commonly used tree. Of the other species found, elm is the most common, with ash and aspen most often found in medieval terraced houses and other homes of the relatively poor. Even when stone and later, brick were readily available, timber-framed structures were still the dominant form of building across the country until well into the 1600s.

Felling the trees

Oak was a carefully managed timber resource in the forests of England. Because of the difficulties of transportation over poor roads hundreds of years ago, most buildings would have been constructed from locally sourced materials and we presume that Bishops’ House and the other buildings of the village of Norton Lees would have been built of timber from local woodland. Even now the small remnant of woodland at Gleadless Valley is no more than 1,300m away. Two sources refer to this woodland in 1462 and 1583. Despite the constant demand on oak forests, some substantial timbers were used in Bishops’ House, showing that well into the sixteenth century large mature oak trees were still being felled.

Seven of the longest measured beams at Bishops’ House are between 6 and 7 m long. The longest four beams measure over 7.5 m, over 8.2 m, 9.5 m and 11.0 m, showing that in the mid sixteenth century, much longer pieces of timber were sometimes available.

Traditionally the trees would have been felled at the end of the autumn, perhaps November or December, and left to weather over the winter, but no longer. Green oak was workable with the iron saws and adzes available at the time but once its moisture content became too low the oak would have become too brittle. So by early the following year, perhaps January or February, the timber would have been sawn into the main beams and smaller timbers such as the braces and rafters. By the Tudor period the growth of the tanning industry meant that it became profitable to fell the trees in the spring when the bark was easiest to remove and could be sold to the tanners to cover the cost of felling. We don’t know if this happened with the timbers for Bishops’ House.

Sawing and marking the timbers

Timber-framed buildings were always prefabricated; the beams cut to size and the joints cut and fitted in the carpenter’s yard. The main beams would have been placed on trestle tables and moved to lie at a right angle before the mortice joint was cut. They would then have been marked with an ‘X’ with two parallel lines bordering it. Twelve of these levelling marks have been found at Bishops’ House. See Figs 2 and 3

Fig 2 – Cutting the mortice and tenon joint and marking the timbers in the carpenter’s yard.

Fig 3 – Carpenter’s levelling mark on one of the posts

Other marks, usually scored with the flat end of a chisel, were used to indicate which of the timbers were to be jointed to which others and many of the beams preserve these marks; usually scribed as a series of modified Roman numerals but sometimes as C shaped marks with a different type of chisel.

Assembling the building

Once the main beams had been cut to size and their joints also prepared, they were assembled into frames in a framing yard. The frame; the part of the structure containing the posts, the floor beam, the tie beam, the king post and the principal rafters would have been fitted together while horizontal; holes being drilled to connect the beams and slightly tapered round wooden pegs driven into the holes to join the beams together. See Fig 5.

Fig 5 Pre-assembling the frames in the framing yard.

The prepared beams would then have been disassembled and brought to the site by horse and cart. Timber-framed buildings were usually built directly onto the ground surface, which was probably just roughly levelled. They did not have the foundations associated with brick buildings.

The lowermost level of horizontal beams, the sill plate, would have been supported on temporary blocks of wood. See Fig 6.

Fig 6 The site is levelled and the lowermost beams, the sill plate are jointed, at first supported on wooden blocks to ensure that the timbers are level. Pads of stone called stylobates were placed at the corners to support the corner posts. Depending on the size of the building, intermediate posts would also have been supported on stylobates.

At Bishops’ House the main posts, wherever visible, have been placed on a pad of stones, sometimes called a stylobate. Their purpose would have been to make sure that when the horizontal timbers were jointed, that these were level and, of course, to keep the posts off the ground to avoid damp and rot. These stylobates often comprise several stones, presumably attempts to do some final adjustments to make sure that the horizontal beams they were attached to were truly horizontal. Measurements of some of the upper beams at Bishops’ House have shown that even after nearly five centuries they are level to within one or two centimetres over five metres.

Fig 7 Final assembly. The main beams are jointed and pegged. The temporary supporting blocks are replaced by a stone supporting wall.

The smaller timbers would have been slotted in with wooden pegs and the space between these filled with small pieces of wood called laths, or even with slates and plastered over. In 2011 when Sheffield City Council was repairing part of a wall we were able to photograph this rarely-seen part of the structure. See Fig 10.

: Fig 8 – Vertical posts, horizontal beams and angled braces held together by wooden pegs in Bishops’ House

: Fig 9 – A scarf joint pegged together to connect two sections of Purlin in the Chamber above the Hall

: Fig 10 – Wooden laths, tiles and plaster revealed during repairs in 2011

Terms used in the text for the major parts of a timber-framed building

Sources

Brunskill R W (1997) Brick Building in Britain. Victor Gollancz.

Harris R (1999) Discovering Timber-Framed Buildings. Shire Publications Ltd.

Jones M (1989) Sheffield’s Woodland Heritage. Sheffield City Libraries.

Rackham O (1986) The history of the countryside. Weidenfeld & Nicholson, London.

Yorke T (2010) Timber framed buildings explained. Countryside books.

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