Flat casing can be applied in two ways – with a mitre joint or with a butt joint.
Mitre Joint
A mitre joint is when the head and leg pieces of casing meet at a 45 degree angle.
![](https://learn.reeb.com/wp-content/uploads/2022/04/kb-interior-mitrejoint.jpg)
Butt Joint
A butt joint is when the head and leg pieces of casing meet at a 90 degree angle.
![](https://learn.reeb.com/wp-content/uploads/2022/04/kb-interior-buttjoint.jpg)