This was a challenging project involving a broad array of structural design, from building-fabric conservation to careful handling of contemporary details. We organised a detailed survey of the building fabric and defects. Measures were then developed to stabilise the existing structure while incorporating the extensive wall openings.
Finally the new architectural components were developed in detail.
REPAIRS Three patterns of traditional timber trusses were surveyed, analysed and repaired. One of the 'farmer-modified' south-end trusses had a totally decayed principal bearing, turning the roof into an untied mechanism that had slowly pushed the wall at the south-west corner out by 250mm. Preserving the form of this severely damaged structure required the following: localised strengthening of the foundation; fixing a supplementary steel-framed floor diaphragm over the loft floor; casting a reinforced concrete ring beam on the wall tops; reseating all the carpentry joints with new, riven-oak dowels; cutting out and splicing in all decayed timber sections; and generally uprating connections between all new and retained elements with new fixings.
ALTERATIONS Forming the 5.5m horizontal slot opening was subject to a planning condition that the rubble fill wall over be maintained.
We specified a full letterbox frame of an in situ reinforcedconcrete backing beam cast integrally with a galvanised-steel face angle. Other new openings were made with reinforced, cast in situ concrete lintels that had composite-acting cantilevering steel soffit plates to carry the facing stonework. A three-bay-wide opening to the east wall of the smaller barn involved the design of slimline iroko portals, which feature hidden connections to the carpentry joints.
FEATURES Our solution for the timber spiral staircase made use of 50mm-thick, finger-jointed European oak. The grain orientation and cut from the log were carefully specified by us. Specific detailing of the arrangement and fixings provided moment connections at the top and bottom of the stair, while allowing for cross-grain expansion and contraction. We used all available means to verify the stair design: load testing a 1:5 scale model; a 3D beam grillage analysis; and a finite-element analysis model.
The final confirmation, in the form of a load test carried out by us on site, was necessary due to the inherent 3D variation of timber properties. We also designed the 3.5m-high, free-standing curvedglass stair surround screen using FE analysis, as well as the other free-standing and cantilevering stone, glass and steel elements that were involved.
Steve Atkinson, Built Engineers