Defining the root directory

[Rich]

Hello,

I am currently working on an addon for one of my sites that doesn't encompass the global.php file from vBulletin. With that said, I am having an issue that I am hoping you all can help me with. (I have been playing and researching now for over an hour.)

This is the basic structure I have:

Root
Sub Folder
Sub Folder 2

Everything is pretty cut and dry when I am using any of my files in the root folder. The issue arises when I am in the Sub Folders.

I have a new page in a sub folder that calls on the header file in the root folder. That is easy enough to get called by simply typing ../header.php. The problem though is that header.php calls on 3 files also in the root folder.

Instead of including the file from the root folder, it is trying to locate the file in the sub folder, which obviously doesn't exist.

How can I go about correcting this without having to duplicate the files being called? I know there is a way to define the roots directory globally, but I haven't been able to figure out how.