Timber post and beam construction

Timber has been the main building material under hundreds of years. It was widely available in Europe and was overwhelmingly used until steel and concrete became the materials of predilection at the beginning of the 20th century. In the history of bridges, even though timber was probably the first material used, the use of stones and masonry has lasted as the dominant bridge material from the ancient Romans time to the introduction of steel and concrete at the end of the 18th century.

The ductile behaviour of timber connectors and their ability to dissipate energy have also played a major role in the wide use of structure made of wooden timber in earthquake region like Japan. In Europe, most of the bridges in service today have either steel or concrete superstructures. Few main road or pedestrian bridges are made of timber. It is nevertheless important to point out that some of these timber bridges have successfully shown the possibility to design heavily loaded bridges with timber (Vihantasalmi bridge, Finland; Flisa Bridge, Norway).

These achievements would not have been possible without the introduction of Engineered Wood Products (EWP) in the arena of timber materials in order to overcome the natural limits of timber as a structural material. Early use of EWP like glulaminated timber (glulam) in structure is for instance visible at the railway station in Stockholm, which has been standing for more than 80 years. Since the beginning of the 1960’s, researches have been carried out in order to reintroduce timber as a competitive material in structural design. A further step in increasing the mechanical properties of glulam was to reinforce it with stronger or stiffer materials. Wandgaard (1964) used metallic plate, and reported positive results.

Timber post and beam construction is a building method that comprises vertical structural posts and horizontal beams, jointed to form a structural frame into which walls are ‘placed’. As this frame is structural, and carrying the roof load, the number of interior walls can be reduced, making it suitable for creating open plan spaces.

Timber post and beam construction differs from the technique referred to as ‘timber frame’ construction, which is a system of panelised structural walls and floors constructed from small section timber studs and clad with board products. For more information, see Timber frame.

Post and beam construction dates back to the 1600s, and typically comprised timbers which were hand-hewn and jointed using hardwood pegs or slotted on top or alongside one another. Oak timber was traditionally used for the beams and columns, as well as the floors and roofing. Sometimes, diagonal posts would be required to resist lateral loads. Contemporary post and beam construction often uses engineered glulam, or modular techniques whereby sub-sections are prefabricated before being hoisted and bolted in place on-site.

It is usual for beams to be visible inside the building, while an exterior skin fully conceals them on the outside which may be rendered or otherwise clad. This can means that post and beam buildings are difficult to recognise when viewed from outside.

Post and beam construction is very flexible and can be used to create interesting and dramatic features. For example, an entire gable end can be used for a double-height window, using beams at the top of the glazing to bear the load of the roof. Late changes and modifications can also be made during the construction phase.

However, post and beam construction can be more expensive than timber frame, due mainly to the additional labour that is required to erect it. It can also be more time-consuming to construct.