In construction, a king post is the vertical timber or strut at the centre of a roof truss, running from the ridge beam down to the tie beam or wall plate. The king post supports the ridge and distributes the roof loads to the structure below. This has nothing to do with an estate agent — it is a purely structural component of a roof.
Position in the roof structure
| Component | Function |
|---|---|
| King post | Vertical strut supporting the ridge |
| Ridge beam (ridge purlin) | Horizontal timber at the top of the roof |
| Tie beam (wall plate) | Horizontal timber on the wall on which the roof rests |
| Rafters | Diagonal timbers from ridge to eaves |
| Struts | Diagonal braces that stabilise the king post |
How the king post works
The king post stands as a vertical column within the roof structure:
- The ridge purlin rests on top of the king post
- The rafters bear against the ridge purlin
- The king post transfers forces vertically downward
- Via the tie beam, the loads are transmitted to the walls
- Struts or braces prevent the king post from toppling
Types of roof trusses with a king post
- King post truss: traditional truss with a central king post
- Scissor truss: simple truss with king post and two struts
- Triangular truss: king post with tie beam and two rafters
Tips for the DIYer
- The king post must always stand on a load-bearing wall or beam, never on a free span
- In older roofs, check whether the king post is affected by rot or woodworm
- Connections to the ridge and tie beam must be secure (mortise-and-tenon or steel connectors)
- Never remove a king post without structural advice
Related terms
- Ridge purlin: horizontal timber at the highest point of the roof
- Tie beam / wall plate: timber on the wall on which the roof rests
- Truss: the entire load-bearing framework of a roof
- Brace: short diagonal support timber