Flooring underlayment is installed primarily to provide a smooth, even, and predictable surface for flooring installation. Does it work for sound, though?
The Problem of Unwanted Sound
Footfall and other noises seep downward, to the floor below. Sound from below migrates through ceilings. Even within rooms, flooring, walls, and furniture act as sound boards that amplify and help sound to bounce around.
Can underlayment be used to absorb sound between floors and even within rooms?
What Do We Mean By Underlayment?
Underlayment can refer to a soft layer, such as foam or cork, placed on top of the subfloor before installation of the flooring. This type of underlayment is typically installed under carpet or laminate flooring.
Alternatively, underlayment can be a thin, hard layer of cement board or plywood. This underlayment may be used under laminate flooring, ceramic or porcelain tile, solid hardwood, or engineered wood flooring.
It is even possible to use both types of underlayment in conjunction with each other.
Soft flooring underlayments are the type that come in rolls of typically 100 sq. ft. and are made of foam or cork. Keep in mind that any foam underlayment, regardless of its physical properties, will most likely advertise that it is effective against blocking sound. While true, it's important to distinguish between this type of underlayment and others that purport to be "acoustic underlayments."
1. Polyethylene Foam
Foam underlayment which does not purport to have special sound-blocking properties is your best bet economically. This type of closed cell foam is easily obtainable and comes under many different brand names. SimpleSolutions Soundbloc Foam Underlayment is one such brand.
2. Acoustic Foam
Foam underlayment that is marketed at being effective at keeping floors quiet. WhisperStop is one brand of acoustic foam underlayment and runs about $60-$70 per 100 sq. ft. roll. WhisperStop is 3mm thick, half the thickness of many cork underlayments. The Silencer is another one: a fairly dense 20 pounds of sound-absorbing material per cubic foot.
3. Felt Underlayment
Recycled felt underlayment is both green and effective. About twice as expensive as polyethylene foam, felt underlayment is a wise choice if sound absorption is your main objective and your budget can handle the added cost.
1/4" to 1/2" AC grade plywood is a popular wood underlayment for laminate flooring, engineered, or hardwood flooring. Plywood provides a moderately-adequate sound blocker. Red rosin paper, which has no sound-blocking advantages, is sometimes laid on top of the plywood to help control moisture.
2. Cement Board
3. Acoustic Underlayment
You can do better than typical plywood underlayment by installing specialized acoustical underlayment.
This product isn't easy to find (we have listed one distributor in the link section) but is designed specifically to mitigate sound. SoundEater is one such product that is made from 100% recycled wood. At 1 1/16" thick, it's clearly thicker than most ordinary plywood products, though make sure that your home will accommodate it. Installing this underlayment below wood sleepers will further inhibit sound transmission, but your height problems will be even greater.
An aggregate of methods--some quite simple, such as adding area rugs or switching out hollow core doors for solid doors--is your best bet for reducing noise. Underlayment alone will not do it, and some types of underlayment (e.g., foam) are practically worthless for this purpose.
Breaking vibration contact with sleepers under the flooring is the single best method of slowing down sound.
But this is a highly complex method that involves subfloor construction and elevating the floor level.
Easier is installation of thick recycled felt underlayment--400% heavier than foam and thus denser. This is your best bet with engineered wood and laminate flooring.