Timber Frame: Light vs. Heavy
A framed structure in any material is one that is made stable by a skeleton that is able to stand by itself as a rigid structure without depending on floors or walls for stability. Materials such as wood, steel, and reinforced concrete, which are strong in both tension and compression, make the best members for framing. The heavy timber frame, in which large posts, spaced relatively far apart, support thick floor and roof beams, was the most common type of construction in eastern Asia and northern Europe from prehistoric times to the mid-19th century.
In North America, which has abundant softwood forests, light timber frames descended from the 19th-century heavier timber frame. These present-day “platform” frames are made of standard-dimension timbers, usually two or four centimetres (0.75 or 1.5 inch) thick which are joined together by machine-made nails and other metal fasteners using hand tools. The older and traditional heavy timber frames used only wood dowels and pegs to create the post and beam bonds. Cheaper and better production of metal fasteners and nails have led the way towards a more modern approach to building.
The American light wood frame (balloon frame), composed of many small and closely spaced members could be handled easily and assembled quickly by nailing instead of by the slow joinery and dowelling of the past. Construction in the two systems is similar, since they are both based on the post and beam principle. Posts rest on a level, waterproof foundation, composed predominantly of masonry or concrete, on which the base member is then attached. Each upper story is laid on crossbeams that are supported on the exterior wall by horizontal beams. Interior walls give additional beam support. Folllowing the creation of the skeleton, the walls are sheathed on the outside with panels of plywood or particleboard to provide a surface to attach the exterior cladding and for lateral stability against wind. The light frame is then usually enclosed with vertical or horizontal overlapping shingling or boarding for weather protection.
In the heavy timber frame system, the beams are strong enough to allow the upper story and roof to project beyond the plane of the ground-floor posts, increasing the space and weather protection. The members, like in light frame construction, are usually exposed on the exterior. In China, Korea, and Japan, spaces between are enclosed by light screen walls, while in northern Europe these spaces are partly by thinner bracing members and partly by boards, panels, or (in half-timbered construction) bricks or earth.