I really don't know. I don't recommend this method, but this is what I do:
adduser non-root-user www-data
chmod 2775 /var/www
chown root:www-data /var/www
# Set HTTPd to use umask 0002
# Only work in /var/www with umask 0002 at non-root-user
Not the way to do it, but I don't know much about...