Everything from the floor under your feet to the ceiling in the room below can have an impact on sound transmissions from
one space to another. This includes the floor covering, any underlayments, insulation between floor joists, adhesives,
acoustic sealants, and more. Let's take a look at these materials and how they can be used to reduce sound transmission from
one space to another.
Underlayments
Often laid under floor coverings, underlayments can help to cushion the floor, making them one of the easiest methods of
reducing sound transmissions. Sound deadening underlayments include cork, rubber, foam, plywood, and several other types that
are made specifically for reducing sound transmissions or improving acoustics. Generally, the thicker the underlayment, the
more sound transmission it can block.
Ceiling
Gypsum board is the most commonly used ceiling material. Thicker gypsum board ceilings help to reduce sound transmissions
from the floor above. When vibrations from an impact travel through the floor, subfloor, and flooring joists, they can reach
the ceiling in a room below, causing it to vibrate as well, transferring the impact sound into that room. When the ceiling is
attached directly to flooring joists, there is little to dampen that vibration. For this reason, resilient channels are often
attached to the floor joists, and the ceiling is then attached to these channels. The resilient channels act as a shock
absorber, reducing the transmission of sound waves to the ceiling, and thus reducing unwanted sound transfer to these rooms.
This can increase both STC and IIC ratings by a few points.
Insulation Between Floor Joists
You can also install insulation between floor joists to increase the IIC rating of a floor/ceiling assembly. Examples of
insulation materials include, but are not limited to, fiberglass, cellulose, styrofoam, and spray foam. In addition,
insulation is assigned an R–value depending on its thermal resistance. Higher R values mean less heat loss in the space
which usually means more sound absorption as well.
Adhesives And Acoustic Sealants
Glue down flooring applications can often be installed with flexible adhesives which can reduce vibrations and damped
noise transfer to the subfloor. Acoustic sealants are flexible sealants that are applied around the perimeter of the floor
surface where the subfloor meets the wall and around other obtrusions (air ducts, doors, etc). The purpose of acoustic
sealants is to seal gaps in order to block sound waves from traveling between them. The flexibility of these sealants also
allows them to absorb some sound vibration.
Let's look at some examples of floor/ceiling assemblies and their related IIC and STC ratings.
| Ref | Diagram | Topping | IIC Rating | STC Rating |
| 1–1 |
 |
3/4" wood flooring over 3/4" plywood subfloor. 1/2" gypsum wallboard nailed
to joists from underneath |
52 |
38 |
| 1–2 |
 |
Carpet and foam carpet pad on 1/2" plywood underlayment over 1/2" plywood subfloor.
1/2" gypsum wallboard nailed to joist from underneath |
56 |
45 |
| 1–3 |
 |
Carpet and foam carpet pad on 1/2" plywood underlayment over 3/4" plywood subfloor.
1/2" gypsum wallboard secured to resilient channel attached to joist from underneath |
70 |
52 |
| 1–4 |
 |
Laminate flooring on 1/2" sound deadening board over 3/4" plywood subfloor. 1/2" gypsum
wallboard secured to resilient channel attached to joist from underneath |
77 |
52 |
Caption: The pictures above show examples of different STC and IIC ratings that can be achieved with
floor/ceiling assemblies. The ratings are an estimate and can differ depending on the actual products and installation method
used.
