Wordpress集成到现有网站 - 使用php包括现有的网站页脚和标题

I have an existing site using html/css/php. I've integrated a WordPress blog to the site and would like to use my existing site's footer and header includes.

www.existingsite.com/blog

My folder structure is set up with my WordPress blog in a separate folder.

existingsite_root -> blog -> index.php

existingsite_root -> inc --> footer.inc

In my blog's index, how do I go up a layer in code to call my existing site's footer?

I've tried this:

<?php require( dirname( __FILE__ ) . '../inc/footer.inc.php'); ?>

However, since this is a string ../ is appended as text instead of instructing to go up and grab the footer file from my inc folder.