[rcme]

You shouldn't be sharing any air with you neighbors, so I doubt ducts are to blame. You can build highly sound-proof timber-framed walls, but most people don't because it's more expensive. Like everything in modern construction, the cheapest permissible option usually wins.

> The apartment buildings I've lived in without central A/C (in Atlanta and San Francisco) were consistently quieter than the ones with central A/C.

When were the units built?

[cwzwarich]

> You can build highly sound-proof timber-framed walls, but most people don't because it's more expensive. Like everything in modern construction, the cheapest permissible option usually wins.

Especially when reduced cost is the reason mid-rise wood construction became popular in the first place.

[unethical_ban]

I don't think it's about sharing air. It's about the duct being in the wall at all.

[rcme]

You can puts ducts in a soffit so they don't necessarily need to be inside the walls. I've lived in two apartments with ducts inside soffits. Both were still very loud.

[scythe]

A soffit must necessarily pass through the wall. Unless it is well-designed, it could cause the same problem.

[rcme]

It passes though a wall, but not necessarily a wall you'd share with a neighbor typically. For instance, in my apartment we had an in-unit air handler with soffits running long the ceiling. We could hear every step on neighbors made. Most building codes require fire separation between units, so you generally wouldn't have duct work running through walls like that as it'd be a path for fire to spread.

[scythe]

How old was the building? Currently I'm in a noisy building — it was built in 1890, before rock wool was invented, to say nothing of fiberglass. It definitely tracks that floors tend to be worse than walls (especially bad with Euclidean zoning that encourages low ceilings and thin platforms).

[rcme]

The building was built in the 90s. Ultimately, the construction was very cheap.

[scythe]

>When were the units built?

1962 (Atlanta) and 1978 (San Francisco).