If you can communicate random text, you can layer E2E encryption over almost any communication medium. OTR is a great example of this. But it isn't a feature of the protocol.

Many irc servers listen on an ssl port, but this then only encrypts data between client and server. The data is decrypted on the server and sent to other clients. (Maybe encrypted)

Some ircd's support "encrypted only channels" where if you're not connected via ssl, you can't /join