BuddyPress.org

@1a-spielwiese The better guide to use in making a full-width page for the theme you’re using, https://wordpress.org/themes/reddle, is the one for Twenty Twelve at https://codex.buddypress.org/themes/bp-theme-compatibility-and-the-wordpress-default-themes/twenty-twelve-theme/

HTML structure for Reddle and Twenty Twelve are almost identical. However. for Step 4 of the Full-Width instructions, instead of using body.buddypress .site-content in media query, add the following to your child theme’s stylesheet:

@media screen and (min-width: 600px) {
       body.buddypress #primary {
              width: 100%;
       }
}