Homasote® building products have been used successfully for decades to help deaden sound in all types of residential and commercial construction. Combined with - or added to - conventional partition and floor systems, 440 SoundBarrier® will reduce transmission of airborne and impact sounds.

The cellulose fiber structure of 440 SoundBarrier lends itself to the reduction of airborne sound levels (STC rating) by acting as a vibration isolator. Homasote's unique manufacturing process randomly distributes the cellulose fibers in a homogeneous mass which creates a building board with a strong yet discontinuous construction. This internal structure, combined with limited mechanical fasteners, helps break the path of sound vibration.

In addition to breaking the path of airborne noise, the natural resiliency of Homasote reduces and isolates impact noise. This is reflected in high IIC ratings. Used as an underlayment, Homasote separates the finish floor from the base structure, creating a sound barrier.

The following construction procedures should be followed so that the laboratory results obtained by Homasote products can be translated into satisfactory field performance:

• To eliminate noise paths around fixtures, outlets or ducts, pack with acoustical batting material and caulk completely.
• Caulk at floor, wall and ceiling peripheries or wherever walls meet floors and ceilings, to eliminate noise leaks. Apply a continuous sealant over top plates and under bottom plates or track.
• Avoid back-to-back locations for outlets; stagger electrical or antenna outlets so that each is isolated within two studs of the partition. Seal openings around ceiling fixtures air-tight.

Impact Insulation Class (IIC): Single-number rating that indicates the amount of impact noise isolation provided by a floor/ceiling assembly. The higher the number, the better the floor/ceiling assembly.

Sound Transmission Class (STC): A single-number rating that indicates the sound transmission loss of a partition or ceiling system between adjacent closed rooms. STC Ratings are:
 25 Normal speech can be understood quite clearly
 30 Loud speech can be understood fairly well
 35 Loud speech is audible but not intelligible
 42 Loud speech is audible as a murmur
 45 Must strain to hear loud speech
 48 Some loud speech is barely audible
 50 Loud speech is not audible

Homasote sound test results are stated in STC and IIC ratings.