So I am using WordPress for a long time but now I've stumbled accross a problem and looking for some advice.
I have my own PHP website running in root, it has index.php page and several sub-pages (help.php, contact.php, search.php, about.php, ...). It is a fully functional website written with my own code.
Now I'd like to add WordPress and use it in several subdirectories for more dynamic content or news categories. In the style of http://www.sitename.com/dir1, http://www.sitename.com/dir2, http://www.sitename.com/dir3, http://www.sitename.com/dir4
Where my own PHP script would remain like it is (on root sitename/index.php with several .php pages unrelated to WP).
My question is, where to install WP (to root, subdir?) and how to set it up properly so it does not mess up my own PHP part of a website?
(Shortly... I have my own website that runs index and several other sub-pages, with wordpress running for all categories / subdirectories.)