What is post-and-beam construction?
Post-and-beam construction is a building system in which a grid of heavy vertical posts and horizontal beams carries the entire load. The walls between them are infill: they carry nothing and can therefore be arranged freely, closed in or left open. It is one of the oldest building principles there is, and it underlies both the Greek temple and the modern skeleton frame in steel and concrete.
How it works
Load from roof and floors arrives on the beams, which take it through the posts down to the foundation. Because there are few points of support, each point is heavily loaded: every post needs a pad foundation or a pile beneath it, not simply a slab.
The weak point of post-and-beam is stability. A grid of posts and beams can deform into a parallelogram. That is resolved with:
- Knee braces in the corners between post and beam;
- Wind bracing or diagonals in the plane of the wall or roof;
- Diaphragm action, for example sheathing or a masonry wall acting as a stiff plate.
Difference from timber frame
| Post-and-beam | Timber frame | |
|---|---|---|
| Load-bearing elements | Few, heavy | Many, light (studs at 400-600 mm centres) |
| Walls | Infill, non-load-bearing | The wall itself carries load |
| Connections | Often carpentry joints (mortise and tenon) or steel | Nailed and screwed connections |
| Appearance | Structure stays visible | Structure is concealed |
In the northern European tradition the timber-framed barn bent — two posts with a tie beam, joined by braces — is the classic form of post-and-beam.
Application and practical points
- Carports, verandas and garden shelters are the most common DIY application of the principle.
- Keep timber out of the ground. Set each post on an adjustable post base on a concrete pad, with the bottom of the timber a few centimetres above ground level. Timber in contact with soil or standing water rots, durable species included.
- Design the connection, not just the beam. In post-and-beam the beam rarely fails; it goes wrong at the joint. Use through bolts with washers rather than screws alone, and account for uplift in the connection under wind load.
- Allow for shrinkage. Heavy solid timber shrinks mainly across its width and thickness as it dries, hardly at all in length. Bear that in mind when placing several bolts one above the other.
Related terms
- Frame bent
- Column
- Beam
- Post base
- Timber frame construction
Looking for more DIY plans? Check out fredsdiyplans.com.