To use both CalDAV and CardDAV in the same account and just using the host name as URL, configure well-known URLs (recommended).
CalDAV/CardDAV path: /remote.php/dav/ (e.g. https://server.example/owncloud/remote.php/dav/)
OwnCloud 8 and below:
CalDAV path: /remote.php/caldav/ (e.g. https://server.example/owncloud/remote.php/caldav/)
CardDAV path: /remote.php/carddav/
Contact group method: groups are per-contact categories
User name and password: same as in ownCloud
(LDAP authentication may cause problems with certain OwnCloud apps)
Most problems can be fixed by upgrading to the newest OwnCloud version (don't forget to update the Contacts, Calendar and Task app, too).