A beginner’s guide to Post and Beam

Post and beam was used for London's award-winning Black and White Building; © Waugh Thistleton architects

In this extract from Timber Typologies – TDUK’s handy introduction to the main timber construction methods – we take a look at post and beam construction.

Combining MMC Category 2 and 3 products, and evolving from lightweight timber frame construction, post and beam systems rely upon the load-bearing capabilities of a skeletal framework composed of slabs, beams, and posts. Utilising the enhanced strength of mass timber components means that taller, longer span structures can be built compared to a lightweight frame.

Components
Glued laminated timber and laminated veneer lumber are the materials typically preferred for columns and beams due to their strength over long spans; floor slabs in this system tend to be made of solid CLT panels.

The vertical posts and horizontal beams are usually connected using hidden steel components, however visible steel bolts, large screws and even wooden fasteners can also be used.

As the building increases in height, the total load distributed down the columns is reduced and therefore column sizes can be smaller which optimises material efficiency and reduces cost.

Structural systems
The most cost-effective and materially efficient grid is approximately 6m x 6m, although larger spans are typically used in commercial applications.

post and beam diagram timber typologies

Diagram showing an example of a post and beam design.

Bigger spans necessitate larger components and deeper beams can have a substantial impact on floor to ceiling heights. Reductions in component sizes can be achieved using different configurations – e.g. by using two shallow beams at each column line rather than a single, deep beam or the introduction of service corridors with shorter spans. Columns should be specified to span no more than three storeys vertically due to constraints on transportation and installation.

The post and beam system facilitates larger spans which increases the flexibility of the internal layout. As such, it is ideal for open plan applications like office buildings. Since only the posts and beams provide the load-bearing structure, the system allows for the future adaptability of the building’s interior by facilitating reconfiguration of internal partition walls and allowing vertical connections to be made between floors through voids in the floor slabs.

Level of prefabrication
Post and beam construction is considered Category 3 MMC with structural elements prefabricated off-site before internal partitions, services, insulation, external cladding and internal finishes are installed on-site.

Construction time
Post and beam can offer significant savings due to the prefabricated nature of the structural elements. Additional savings are achieved during construction due to the ease of erection and the accuracy of the finished structure.

Ease of transportation
Beams, columns and floors can be stacked compactly with no wasted space, offering a reduction in the number of deliveries to site compared with concrete frame.

Layout flexibility
Post and beam systems are ideal for applications where flexible layouts are a priority as internal walls aren’t load-bearing, allowing the creation of large open spaces.

Demountability
The detailing of post and beam structures can enable structural elements to be disassembled and then reutilised or reused in alternative applications.

This is an edited and condensed extract from Timber Typologies, a guide to all the major timber construction methods. You can download the whole publication for free from the TDUK website.