I find it hard to believe a metal and wood chimney grafted to the top of a brick chimney is preferable to a lined brick one. Quote the ordinance for us.

Thanks for the healthy skepticism. I was just taking the inspector's word on it. Now I've done a bit more looking.

This is almost certainly because of location: the SF bay area, the two key factors being air quality and earthquake risk.

I can't find the rebuild restriction in my town ordinances (which aren't too easy to read online) but:

1. New wood burning fireplaces are pretty much prohibited anywhere in the SF bay area by the Bay Area Air Quality Management District. I knew this.
2. Reconstruction from the top of the firebox is what FEMA recommends for repair of earthquake damage.

I had a masonry liner pumped into my 100+ year old chimney to stabilize from top to almost bottom. It's invisible from the outside.
Flue liner

Somehow I don't think that will fly in California with our earthquake-inspired building codes (e.g., they have no installers in California.)

Thanks though :-)