> The sound insulation between flats on a converted office building must be nil.

A lot of the older buildings in SF just have 2x4 walls separating the apartments, with fiberglass insulation. It's not very good at insulating sound either.

If the office conversions are done properly they will be better at sound insulation than much of the existing housing stock in SF.

The real question is, why bother renting in SF when any of the surrounding cities are cheaper? Most of the reasons to live in SF (restaurants, nightlife, cultural events) are shut down indefinitely, and commute distance isn't relevant if you are working from home. Renters can get a lot more for their money in the East Bay or the Peninsula.

> The real question is, why bother renting in SF when any of the surrounding cities are cheaper?

Because the pandemic-related shutdowns are temporary (though of course there will be lasting effects), and rents are 30% off their highs, with many landlords throwing free months and other incentives at people to get them to rent.

Sure, if you need/want to save some money over the span of the next 8-12 months, moving out might be a good idea, but if you want to live in the city, you're going to move back eventually, and moving itself isn't free. I think that's a thing that people seem to be missing: posts like yours seem to suggest that the only or main reason people live in SF is because their jobs are there and they want a short commute. That's... just not the case for many, many people.

I think there are valid arguments for leaving, valid arguments for staying, and valid arguments for moving in. But it depends on each person's individual situation and wants and needs.

Thankfully you can do sound isolation without concrete. If they do that or want to save money is a different topic I guess.

Concrete separation also acts as fire barriers, which is very important in areas where people will be cooking stuff. Office buildings don’t typically have stoves with open flame everywhere.

Most apartment buildings in the Bay Area are made of wood with 2x4 wall framing and sheetrock, except for a relatively small number of high rise buildings. We haven't really had a fire problem.

I would assume that office buildings aren't set up with gas lines running all over them, so likely these retrofits will include electric ranges and stoves.

There's still a fire danger, of course, with any kind of cooking, but at least there shouldn't be open flames all over the place.

Not for low frequencies. You simply need mass for that, no way around it.

Is mass the only way? The building I worked in had problems due to us transmitting a lot of noise up concrete columns, and it was solved by isolating the source from the columns. Rubber feet were used to separate the noisey equipment from the floor.

So couldn’t you isolate the noise with false ceilings and walls that are constructed to minimise transmissions?

Both is best, but typically a 6" deep wall with offset 2x4 studs, insulation in the wall, resilient channel, 5/8" drywall (which is also fire resistant usually, with fiberglass in the core) and the right caulk and electrical install will stop all but very loud low rumbles.

The key is the installation and design of the system, though. Miss one vent, electrical cutout, or gap (or even using the wrong length of screws) makes all that material useless.

sound isolation yes, but vibration isolation (footfalls, washing machines, subwoofers) no way.

source: I tried very hard to soundproof between floors. Sound passage is non-existent but footfalls are plainly heard.

> Concrete separation also acts as fire barriers, which is very important in areas where people will be cooking stuff

Sheetrock (gypsum) can solve this problem if you use enough of it. But that can get expensive.

Usually fire code mandates a 2 hour fire rating for each unit, so you end up with two parallel air gapped 2×4 walls that have sufficient sheetrock on the one side facing the unit the wall was built for to get that 2 hour fire rating.

I've seen one of the offices where I work while it had the ceiling removed for renovations. There were probably 4 feet of space between the ceiling and the floor above. I've also seen the same thing in my apartment and there was about 1 foot of space. I don't think noise will be an insurmountable problem.