Ownership of VM docroot (yet again)

I am a professional dev but this is is driving me nuts.
After the two last updates, all my VMS are owned by www-data
Using the fix permissions utility changes the all to owner - ok cool, but the folder is really owned by www-data and it falls down in a sad heap (500)
Change owner back to www-data and it all works again. I have read a dozen posts or more on this, with nothing suggested working.