Glulam timber roof

A large-span roof structure made of glued-laminated timber — spruce boards glued and pressed into beams, arches or trusses as large and straight as steel, but light and warm. Glulam reaches spans solid timber cannot, with a low self-weight and a fine exposed soffit; heavy timber chars slowly and predictably in fire, while the steel connections are the point to design and protect.

A glulam roof is a large-span roof structure made of beams (or arches, or trusses) of glued laminated timber — spruce boards glued and pressed into elements as large and straight as steel, but light and warm. It is the structure of gyms, churches, pools and halls.

Glulam reaches spans solid timber cannot — tens of metres — with a low self-weight: the roof bears lightly on columns and foundations. The beams can be shaped at will (straight, curved, pitched), and the exposed soffit is warm and fine, part of the architecture.

Against intuition, heavy timber resists fire well: it burns at the surface forming a layer of char that protects the core, and the section reduces slowly and predictably. The beam is therefore sized with a sacrificial oversize for the required time. It is often the steel connections, not the wood, that are the point to protect.

The delicate point is the joints: bearings, splices and connections are made with steel plates, dowels and brackets, to be designed with care because they transfer all the forces. Tall, slender beams must be braced laterally — with purlins and roof bracing — so they do not buckle. The bearings are kept dry and ventilated so the ends do not rot.