Round rafters are called chuan, square ones are called jue.
Tips
usage
A 桷 is specifically a square-sectioned roof beam, while a round one is a 椽. The word is largely literary and architectural and rarely heard in everyday speech today.
Supplies the sound. Standalone 角 can also read jué, close to this character's reading. Its 'angle / corner' sense fits faintly, since the rafter it names is square-cornered.
