It depends a lot on where you are. Warm parts of the US will build houses with 2x4s and uninsulated interior walls+floors. In the northern US the exterior and

It depends a lot on where you are. Warm parts of the US will build houses with 2x4s and uninsulated interior walls+floors. In the northern US the exterior and even sometimes interior walls are 2x6 and have high quality insulation in the walls, floors and ceilings, plus nowadays there's quite a thick layer of foam on the outside. The extra strength and rigidity does a ton of work attenuating noise from other parts of the house, and the walls are much harder to transmit sound through.