Reconstruction

Thirlings Building A was selected as the first of the experimental reconstructions at Bede's World for three reasons:

It is typical in its overall architectural form of the buildings of the Early Medieval era;
Despite this, it has irregularities in design which posed some interesting problems for analysis and reconstruction;
It is well documented in the archaeological record.

The experimental reconstruction begins with the evidence of the ground plan as recorded in the excavation. The foundation trench was set out to the same shape and dimensions and dug to the depth of the original plus a further 300mm to allow for the topsoil which had been removed pre-excavation. Timbers were set in the trenches in the positions recorded in the excavation, with others added to complete the set where evidence was incomplete in the original in the north-east and south-west sides and at the east end. There are in all 35 wall posts, each the stem of an oak with the bark stripped off, each approximately 300mm in diameter. The 26 side-wall posts (including the four corner posts) were cut to 3.10m in length. A wall plate of square-sectioned oak baulks is attached to the tops of the posts by a loose mortise and tenon joint to give a wall height of 2.0m to the underside of the wall plate. End-wall timbers, which reach into the roof, are longer; the longest being 6.0m in total (including the below-ground element). The nine end-wall timbers (five at the west end, four at the east) are notched for a tie beam to be fitted at each end which sits on top of the wall plates at the corners. The wall cladding in between the timbers is of limewashed wattle and daub. Wattles of hazel and willow are fixed into the wall timbers in small holes drilled with an augur. Daub has been made from mixtures of puddled clay and straw. It shrinks and cracks as it dries and has needed frequent re-patching. The two side-wall entrances are provided with doors of oak planks which pivot about holes cut into the wall plate and a threshold beam at ground level.

The roof support system follows the excavators' analysis, but with some modifications. Three sets of internal posts, a group of three towards the west, two centrally and two towards the east end, carry a ridge beam and two side purlins. In the west group, the central post carries the ridge beam at a height of 5.3 metres above ground level (measured to the top of the ridge beam). The two side posts carry a collar 3.5 metres above ground level (to the top of the collar) and the side purlins rest on the collar. The central post is notched to fit the collar. The uprights and horizontal members are joined by the same loose mortise and tenons used on the wall lines. In the central and east assemblies which have two side posts and no central post, the collars support king posts which carry the ridge beam.

With the irregularities in lay-out of the building and the shortage of detail recovered from the west end-wall, there is some scope for debate as to how the roof is aligned in relation to the walls of the building. On the excavators' analysis, the ridge beam does not extend to the east end wall which has no central post to support it, while the side purlins can be extended from the internal supports to end wall posts. Thus they proposed a half-hipped roof form at the west end and matched it with a similar arrangement at the east. In the Bede's World reconstruction, the roof line is placed at a slightly different angle in order to extend the ridge beam to a west end wall post which is positioned a little to the north of the mid point of the wall line. In this way, a gable end is formed in which the pitch of the roof is slightly steeper on the north side than the south. On this alignment, the side purlins do not precisely meet end wall timbers. A principal rafter is used at the end wall and the side purlins are notched in to this.

At the east end a post is positioned at the centre of the wall line to form another gable. To allow for the narrowing of the building at its east end, the side purlins are angled inwards from the central supports and both the side purlins and ridge beam, which are horizontal in the west half of the building, are angled downwards. In this way, the angle of pitch of the roof is maintained along the building while the height of the ridge beam is 0.45m lower at the east end of the building than the in the western half. The ridge beam, which is formed from two timbers lap-jointed at the central support, is angled slightly at the joint to reconcile misalignments in the two halves of the building. The isometric view shows the full roof timbering and support system.

Common rafters are formed from ash poles which rest on the ridge beam and are notched into the outside edge of the wall plates. Wattles of willow and hazel tied to the rafters to give a base for a thatched roof of reed and, at the apex, sedge.

The excavators' analysis of the building offered little discusssion on how the roof support system was to be tied into the wall structures. They interpreted small pits around the outside edges of the building as placings for timbers which were angled to meet the wall at the level of the wall plate, in this way counteracting any tendency of the walls to collapse outwards. But they showed no connections, other than the rafters, between the roof supports and the side walls. In the Bede's World reconstruction, tie-in to the side walls is achieved by an assembly at both sides of each of the three internal support systems. In each case a horizontal tie beam joins the wall plate and internal upright by means of a tusked tenon assembly and angled braces are set from the top of the upright, below the collar, to bear against a tenon of a side wall timber where it projects through the wall plate. This support system also acts against the possibility of the roof racking. The external post pits are judged to have been supporting system introduced during the life of the building and have not been used in the reconstruction.

A hearth has been formed (a shallow scoop in the ground surface) west of centre in the building (following the evidence of another of the Thirlings buildings) and the smoke percolates out through the roof thatch without the need for a chimney. In this reconstruction, the interior is a single open space, though the internal roof support timbers could form the framework for partitions. To provide light in the building, two window openings have been made high in the west end wall, one on each side of the ridge support post. They have been provided with shutters which open outwards. The flooring in the building is earth which, through constant wear and protection from the rain, has hardened to a smooth surface. On the outer surface, the main wall timbers and the limewashed panels are visible.

The main structural timbers used some 30 tons (30,500kilos) of green oak from trees of 50-60 years old. They were sourced from an estate in County Durham. For the roof, 70 ash poles from Suffolk were interwoven with rods of hazel from Cumbria. 1800 bundles of reed were brought from Tayside and 125 bundles of sedge from Cumbria for the roof covering. Willow, hazel and birch from various sources were used to form wattle panels. About 25 tons of boulder clay and straw, sourced locally, were mixed to make daub for the walls. It is a point of some interest that it has not been possible to source all the wood and other materials for this building locally (say, within a 50 mile radius). This invites reflection on the woodland management regimes which were in place to support the vernacular architecture of the early medieval period. Thirlings alone had nine buildings, some smaller and some larger, of the type reconstructed here.