St Edwards School Library

Architects, TSH, appointed the Green Oak Carpentry Company post planning for the technical design phase to assist with the timber structure design and to make key decisions prior to tendering the main contract. The carpentry team was able to guide the client team through the decision-making process and advise the use oak glulam for the structure and to assist in the process of specification, procurement and manufacture.

Nigel Challis from AWA was enlisted for structural design expertise and was invaluable to the project, assisting in overcoming the challenge of achieving portal action whilst utilising slender 315 x 120mm oak glulam beams. This we achieved using an unusual joint design, which we nicknamed the ‘Corbett Knuckle,’ after its inventor Steve Corbett. The solution involved machining large steel billets, sitting into recesses in the joint, with threaded bolts, ensuring a tight moment connection to achieve portal action. Not easy in timber. See drawings.

A further complication was that oak glulam does not yet have enough market share to justify the cost of extensive structural testing and grading, therefore the manufacturers were only able to offer a cautious D30 grade. Nigel was willing to take a view, and prepare his calculations based upon a more realistic D40 grade.

The glulam beams were finger jointed, laminated and CNC cut by a specialist company in Germany. A critical component of the job was the production of meticulous data files prepared by the specialist carpentry team’s draftsman. The CNC cutting of the joints allowed the use of a tapered dovetail joint, critical in assisting and enabling the assembly process.