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Comment by Johnny555 | Hacker News Reader

Can wood buildings provide good sound isolation between floors?

I've lived on the 3rd floor of a wood framed 4 story apartment building, and won't repeat that experience if I can help it -- we could hear the couple upstairs very clearly, footsteps, their dog jumping off the couch and barking out the window, late-night sex, all were easy to hear.

In contrast, I lived on the 5th floor of a 9 story concrete and steel high rise, and couldn't hear anything. I even had the upstairs neighbors ask me if I could hear their new treadmill, and I could not.

I assume that the sheer mass of the concrete floors made it so quiet -- Can a wood framed building be constructed with that same level of isolation?

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I have built my first wood houses since few years, European class A+, short answer is yes however less than concrete houses.

Long answer structure is from lower flat and upper is:

- fibrous plaster + finishing with it's support structure

- mineral wood 100mm think between wood beams (250mmx100mm)

- OSB panel on top of beams, 30mm

- sandwich panel composed of wood wool (20mm) and fibrous plaster (30mm)

- thin (4/5mm) wood wool panel

- laminated floor

If I walk normally I do not hear too much downstairs, otherwise well... Noise passes, far more than classic concrete + rubber coat + background and floor tiles... Also when I move I hear "casual noise" from laminated floor friction. Not much but a bit yes...

IMO sound propagation is due to the fact that wood structures are lighter and elastic than concrete so vibration passes far easier and it's hard to stop them...

Wood framing is not the same as a building built of cross-laminated timber. The architect must get a few details right, but it is straightforward to meet "only able to hear neighbors when jumping off a table on to the floor". OTOH it's not much more difficult to do that with standard wood framing, but they don't usually.

They cannot without involving way more material. The best isolation is the mass of the floor. Try moving around the second floor of a wooden building and check if the glasses in some cupboard start to clash. If they do it is because the floor bends under your weight. The only countermeasure is to increase the mass of the floor and while a wooden wall (if planned for it) could certainly carry that weight it is difficult to obtain that mass from a wooden ceiling.

They can if they purposefully add sound insulation, but it does cost a decent amount more in construction and is hard to add in after the fact. Concrete is quieter without doing anything to it but it also costs from the start.

FWIW, I live in a brick and concrete building and hear all the things you mentioned, sometimes not just from immediately adjacent units, but also often units two or three floors away in some cases, e.g. loud parties or drilling/hammering (the rigid structure conducts the sound around the building I think - kinda like tapping on a metal pole or rail: doesn't matter where you put your ear on the pole you still hear the noise from the tapping)

loud parties or drilling/hammering? in a wooden building (in a pretty regular US home at least) you hear people gently walking or even just coughing on the floor(s) above or below you

Yes there are a few relatively simple things that can be done to vastly improve sound isolation in wood frame buildings. They do cost a little bit so many builders don't do them.

For isolation between rooms the walls can be built with "a hollow core", which means there are, in effect, two separate walls, each facing their respective room with almost no pieces of wood joining the two walls. It's the wood that normally is touching both walls that allows sound transmission. Secondly the "gyp rock" sheets that create the wall can be stood off from the timbers they're anchored to to further improve sound isolation.

For sound isolation between floors it's possible to lay down about four centimeters of concrete over the wood floor and this hugely improves sound isolation.

Obviously these increase costs but they do really work and probably don't increase cost by more that 5 to 10 %.

I've lived in both. In the concrete building I hear nothing. In the wood one I could only hear things that directly made contact with the floor, like people walking, chairs moving etc. I could never hear anything else. But I was slightly paranoid that I was simply the only one in the building who listened to music, had sex etc.

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