I’m not talking about rent control as it is currently done in San Francisco. We need more. Like you say, rent control should also apply when a new tenant moves in. A landlord should not be allowed to raise the rent arbitrarily when a new tenant moves in.
Also rent control should not be the only measure. The county should also buy up housing and rent for cheaper to drive the market rate down, price gauging should be illegal (for everyone, not just foreign investors). etc.
>The county should also buy up housing and rent for cheaper to drive the market rate down
Almost, buying up housing is fine if the government changes zoning and upzones existing properties. It is better to go one tiny step further and make the government guarantee housing for a fixed price because then it is truly forced to fix the problem.
Once you have done this important step the government has many options. It can either fix the demand side or the supply side.
The supply side is easy to fix by changing zoning laws to encourage taller residential buildings and then by actually building them.
The demand side can be fixed by changing the tax law so that commercial property is no longer the only source of property tax income. This lead to an imbalance of commercial vs residential property which then lead to lots of workers without housing which then lead to a race for apartments driving up prices.
You're still missing the most important component for affordability: more housing. Not simply conversion of existing market-sold housing to price controlled, but more.
Lets say that everything gets converted to rent-controlled in an area. A child becomes 18, graduates from high school, and wants to stay close to their family to maintain their emotional connections. If everything is rent-controlled, but not enough housing is built, they have to be on some sort of waitlist or lottery to stay in the area. This will push out so many people.
The only solution is to make enough housing for the people that want to live in an area. Without that, we are rationing it by price, by lottery, or by waitlist, and all of those will destroy the emotional connections that both you and I want to maintain.
Also rent control should not be the only measure. The county should also buy up housing and rent for cheaper to drive the market rate down, price gauging should be illegal (for everyone, not just foreign investors). etc.