Why can't I create Community Sites in a Community Portal?

The Communities workload is a fantastic addition to SharePoint 2013; check out here for an overview of the feature set.

When creating a new Community Portal site collection, it's natural to immediately want to create Community Sites. If your planned Communities Information Architecture is very small – or you’re doing testing or development – then you might want to create Community Sites as sub-sites of the Community Portal.

Unfortunately I've seen several SharePoint 2013 environments now where this is simply not possible out-of-the-box. Attempting to create a sub-site of a brand new Community Portal only offers a limited set of site templates which does not include Community Site:

There's no Community Site option...

This is a little frustrating, but it is easily fixed!

Go into Site Settings for your Community Portal, and select Site Collection Features. Make sure that SharePoint Server Standard Site Collection Features is activated - by default this may not be active:

Once this is done, you can create Community sites:

That's better!

From here, you may find that you receive the following error when attempting to create a Community Site:

Dependency feature 'Ratings' (id: 915c240e-a6cc-49b8-8b2c-0bff8b553ed3) for feature 'CommunitySite' (id: 961d6a9c-4388-4cf2-9733-38ee8c89afd4) is not activated at this scope.

This one is also pretty easy to solve; just run the following PowerShell command will activate the dependent hidden Feature referenced in the above message:

Enable-SPFeature –Identity Ratings –url [site collection URL]

Now you're good to go!