I had a need for a fixed side navigation bar, so I created this fork and pushed the changes. If anyone has suggestions or improvements, please submit a pull request. I would like to improve it, because I am new to Roots and Wordpress themes.
Roots with Side Navbar on Github
The sidebar can use the Primary Navigation or create a new Menu and use it in the nav bar. This is a basic implementation, allowing for a multitude of changes.
I believe it will help a person new to Roots to show an example of how to add a custom part to the theme. All you have to do is follow the initial commits and see the changes made.