Maybe one of SF’s tech companies can invent a technology that would allow housing to be stacked vertically.

> Where do you propose all these new houses be built?

That's your problem right there, when you write "houses". Cities need apartment buildings, which allow more homes per same area than single family houses.

> SF is surrounded by water on 3 sides. Where do you propose all these new houses be built?

Up seems to be the obvious answer.

New construction can replace old construction. In theory.

Let builders tear down old buildings and single dwelling house and build up and denser. NIMBYism prevents this currently because people want to "keep the feel" of the area. Well that's impossible. Things always change, you can't go back, you can only delay and price yourself out of your own house. At least most get to sell at a good profit.

Vertically.

What did Hong Kong do?