> Homebrew wants it to be 775 root:admin
It's worse than that. Homebrew wants 775 $(whoami):admin.
quesera's reply points-out just how bad it is, but even for just 775 root:admin I would have to use sudo (plus edit the sudoers or /usr/bin/login -p first) anyway:
$ /usr/bin/env -i /bin/sh -c \
'id | grep -lw admin >/dev/null && echo admin || echo non-admin'
non-admin
The problem is I have no problem using sudo, but homebrew does (like it wants make all to happen as me).
People keep writing here as if El Cap removes /usr/local entirely. It does not. /usr/local is there by default. You only have to go into recovery mode if you've somehow removed it yourself.