By default, addon and subdomain document roots are restricted to the publich_hml of the account under which they are created. This article covers how to disable this restriction.
1) Log in to WHM and navigate to the following location.
Home » Server Configuration » Tweak Settings
2) Click the "Domains" tab.
3) Change the "Restrict document roots to public_html" setting to "Off."
4) Click the "Save" button at the bottom of the page.