You may consider to have 1/8" or 3/8" of cork underlayment for sound barrier. Floor Muffler underlayment with a very high IIC and STC rating allows you to use under solid wood naildown too.

Thank you. What do the letters stand for?:)

I don't think that a thin layer of cork will muffle the sound of a garage door. If you really want to deaden the sound, you need to use an insulation designed for this in the joist bays. Hopefully the garage door opening and closing doesn't occur too frequently! Be careful if you do decide to use a soft underlayment like cork - you'll need to make sure that your floor cleats (my preference for solid hardwood floor fasteners) or staples are long enough to penetrate deeply enough into the subfloor.

Here is the link about this ratings. I agree with "dseng"'comment.

Here is a link that might be useful: STC & IIC

I'll be having nail-down, finish-in-place hardwood installed throughout the house except bathrooms, which are tile. To even the transitions, I need to bring up the hardwood by about 1/8" to match the level of the tile.

Is cork underlayment a good choice for this purpose? If so, how should it be installed (glued, stapled, other) ?

I have a similar question along these lines ... we are installing hardwood floors, and an underlayment (attofarad, you might want to investigate Regupol & Nobel Seal).

However, we are trying to figure out what's the best option for installing the hardwood floors -- glue down, or nail down?

We have been told that nail down would require 2 additional layers of subfloor so that the nails do not penetrate the underlayment and so is the more expensive option. Though it was our understanding that nail down was preferable to glue down to let the wood expand/contract.

Thoughts on what is preferable?

"We have been told that nail down would require 2 additional layers of subfloor so that the nails do not penetrate the underlayment "...

Is this suspended wood construction? If so, you already have a subfloor layer. I don't understand the 2 additional subfloor layer recommendation.

Hi glennsfc

it would be hardwood, plywood, green glue, plywood, underlayment, subfloor, then the joists

"(attofarad, you might want to investigate Regupol & Nobel Seal). "

Thanks for the references, bu those materials do not seem to be the correct thickness for what I need -- either too thin or too thick. As I said, I need to "shim" the hardwood by about 1/8"

I'm not really concerning about sound attenuation. I will be nailing through the underlayment.