I have a friend in SF who had a tree fall into her house and destroyed half the house. After it was all fixed, the building code people came in and said they couldn't sign off on her final inspection because she hadn't installed sprinklers, which are now required on any new room additions on existing homes. She hadn't installed sprinklers because they hadn't added square footage. However, the previous owners had added a room -- and the sprinkler law wasn't in place at that time -- and they are enforcing this code on her retroactively. I need to call her to see if it has been resolved yet.