Write permissions problem

I had version 4.3.1 and it was working and I upgraded to 4.6.1 and now I am getting a write permissions problem issue when I try to backup.
I tried uninstalling and reinstalling the plugin and tried again but that didnt work. It seemed that after uninstalling from the dashboard the directories (plugin and upload/db-backup) were not removed and so I removed them and then reinstalled from scratch. However the upload/db-backup directory was not recreated so I created it. I used permissions 775.
The plugin still had an error:

WP Database Backup
Error: Permission denied, make sure you have write permission for /home/mydir/public_html/mydomain.com/wp-content/uploads/db-backup folder

I gave it 777 and tried again and that worked. On putting it back to 775 the error occurs again.
The documentation does not give the exact directory permissions needed. It just says you need to be able to write to it. As far I know from what I have read (and in terms of security), no folder in the uploads directory should have permissions of 777.

What are the correct permissions the directory needs?

How can I fix this if at all?

Thanks!