Carpet. Seriously.

GreenGlue also makes some tape for between subfloor and the joists.

EasyMat for tile.

Cork underlayment for wood.

Drywall clips for ceiling below.

Insulation in floor doesn't help the structural transfer, which is most of the problem with floors.

FWIW.

Okay, interesting about the structural transfer not being helped by insulation. We are doing wood floors on the main level, so carpet is out. I will look into cork underlayment--does anyone have experience with doing that?

I may have to do a little Googling. ;)

"The goal is just to deaden the sound of footsteps from those walking on the main level, so that those on the lower level (below ground walk-out, truss system) are not bothered."

About a zero chance other than carpet and padding, or very expensive rework that will cost you head room.

Even metal isolation channel is not very effective since the isolated mass is small.

The ultimate solution is to place a complete false ceiling (including joists to the foundation) and have no connections between the upstairs floor and ceiling.
Depending on the span needed the joists and framing can eat up a lot of headroom, though less than the fully weight bearing framing above them. The only load on the false ceiling is the drywall.

I have the same situation. I also don't want to get into the expense of an STC-45, or higher, rated installation. Batts between the joists will absorb some of the sound waves. However, sharp sounds, such as high heels or hard-soled shoes, will still be easily heard.

brickeyee can weigh in here but I have an unfinished space where I would like to lay down either a carpet pad or 1/4" fan-fold EPS insulation (such as polyshield) before installing wood flooring. The EPS insulation is a little spongy and does not "dent" like polyisocyanurate rigid foam board. This should work well for floating flooring but I am not sure about 3/4" hardwood that requires nailing to the subfloor. I don't know if the cost is worth it but my unfinished space is small enough to use as a test case.

This has been discussed here many time. The short answer is to study the tested details and find one that works for your situation.

Here is a link that might be useful: floor acoustic abatement

A good drywall ceiling support system is IsoMAX.

Here is a link that might be useful: IsoMax

One of the principles commonly misunderstood about sound transfer in a floor is that sound energy is transfered by more than one method and that all methods must be addressed for reasonable success. A completely separate ceiling system interrupts structural transfer but not the indirect transfer through the air space between the ceiling and the floor in both directions.

The most effective solution for a floor/ceiling assembly is to not only acoustically separate the ceiling from the structure but to also provide resilient support for the ceiling in order to avoid indirect sound energy transfer between the rigid ceiling and the rigid floor membranes.

The simplest way to do both of these things is to use resilient channels or h hat channel on special mounting pads like IsoMAX.

Macv -- good info on the IsoMAX system. In my previous work designing secure facilities I had to meet STC-50 ratings. An STC of 61 @ $8/sf is an economical option.

lkz-- like you we wanted to lessen the noise from upstairs and figured we couldn't really stop it completely. We put a layer of foam insulation on the underside of the 2nd floor, and it seems to be working ok. (I'm posting this at the risk of being flamed by people who say it won't work.) It doesn't stop all the noise, but we have a washer and dryer upstairs that we can't hear in our LR when they're running despite the fact it sits directly above.

foam or board insulation? on the bottom of the sheathing or the joists?

Spray foam insulation (open-cell). On the bottom of the sheathing.

Foam insulation (in thickness less than 8 inches) is effective in sealing cracks and may absorb sound that is bouncing around due to cracks in the ceiling but it doesn't address the primary paths for sound transfer through the framing and the air. What is needed is some kind of mass and resiliency.

Open cell foam will absorb some sound. Closed-cell will transmit it just like the wood framing. We are very happy with the results we got, and the foam guys sprayed that on at the same time as they did the walls and roof deck.

"One of the principles commonly misunderstood about sound transfer in a floor is that sound energy is transfered by more than one method and that all methods must be addressed for reasonable success. A completely separate ceiling system interrupts structural transfer but not the indirect transfer through the air space between the ceiling and the floor in both directions."

The problem with noise through floors is that it is low frequency impact noise that IS transmitted.
It is the hardest thing to stop.

Sound insulation works well for filling the volume and stopping noise that is NOT conducted.

If you tie to the surface that can conduct noise you end up needing isolated mass to try and limit transmission.
The mass of the light steel framing and drywall are often not adequate.
you can improve the performance by adding more mass to the drywall (thicker or more layers) but you have to play that against the 'stiffness' of the fastening means. More weight requires stiffer fastening, increasing the sound transmitted.

Concrete floors work very well since they are so massive it is very hard for anything much to be conducted, and fiberglass sound insulation takes care of the rest of the problem.

If you are in a framed structure (wood or steel joists) the most effective method that works every time is a false ceiling with separate joists (sometimes you can put them between the existing joists to get back some headroom) and fiberglass sound insulation.

All the various isolation fasteners end up having problems based on the suspended mass and their relative stiffness.

Oh, man. I think any way you slice it this is going to be out of our means, with our already bursting-at-the-seams build budget.

We are a sock-foot family, so that helps, but we have little boys who have two speeds: "run" and "sleep." The running is a little noisy and we have basement bedrooms.

If you study this subject in depth you will find that resilient systems reduce sound transfer more than even a separate ceiling system.

I know brickeye won't agree but that's what I was told and it has worked well for my projects from a restaurant below another restaurant's kitchen in a former mattress factory with wood deck floors, to a simple double-decker house.

If you have a tight budget you can't beat resilient channels (RC-1) whatever else you do to the assembly. It should cost no more than a second layer of drywall and be far more effective against structure borne and low frequency sound.

Resilient channels are like building felt; the manufacturers don't advertise it or defend it against the claims of more modern systems but you can't beat it for cost effectiveness and contractor's don't look at you funny like they do when you try to explain how to install Green Glue.

I forgot the commercial.

Here is a link that might be useful: resilient channels at Amazon.com

"If you study this subject in depth you will find that resilient systems reduce sound transfer more than even a separate ceiling system."

Bovine scatology.

Conducted transmission requires a physical path to occur.

No contact, no path.

There is NO conducted transmission with a separate ceiling.

None.

Without any physical connection there can be no conducted transmission.

Failure to account for non-conducted can still produce lousy isolation however.

Many designers only address half the problem.

Macv, that sounds like it might be a doable option. You and brickeyee can continue to hash out what would be the most ideal and perfect system, but for *some* reduction and a low cost, the resilient channels idea sounds like it might be a good option for our family. It looks like something DH might even be able to do himself, which is a plus.

I am lol at "bovine scatology." I might have to tuck that away for future use.

The difference in performance between the two designs is not worth arguing about; it's entirely a matter of cost and ease of construction. Take your pick.