I made a child theme for roots and it worked as expected. I can override everything, including footer.php, but not header.php. My header.php looks exactly like the one from roots at the moment, except for the blog title, which I replaced. I googled it, but it seems that I'm the only one facing this problem.
Just to clarify, are you referring to this theme? If so, it doesn't appear to use the architecture of a typical theme - you'll need to copy
child/templates/head.php and modify accordingly.