Building frontend + backend : best practices ?

[eluser]Isuka[/eluser]
Hi guys,

I'm thinking about my development process and I want to know how you guys doing things when you build a website with a backend.

Since I build website with CI, I make 2 separate applications : one for the frontend and one for the backend.

My structure look like this :

Code:

.htaccess
admin
  .htaccess
  .htpasswd
  index.php
applications
  - backend
    - config
    - controllers
    - helpers
    - models
    - modules
    - views
    - ...
  - frontend
    - config
    - controllers
    - helpers
    - models
    - modules
    - views
    - ...
index.php
skins
  - backend
    - css
    - img
    - js
  - frontend
    - css
    - img
    - js
system

I like this structure because the frontend and the backend are dissociated.
I can quickly protect the backend with an .htaccess in the admin folder for exemple.

But the boring things is that I need to duplicate some frontend and backend common libraries and helpers or duplicate models for each app when models are almost the same.

Of course I could make an unique application and make an admin controller in it but I don't like this idea because I think a backend is an application on its own.
I need also to duplicate my config files when there are the same. Kind of things annoying.

(Is this possible to have a common libraries or helpers folder or config file accessible from both frontend and backend app ?)

I'm curious how you guys handles that.