Noise transmission through wall and floor systems is important because the better the system is at reducing noise transmission the more comfortable the living environment.
The New Zealand Building Code Clause G6 Airborne and Impact Sound specifies minimum requirements for noise
transmission reduction for walls and floors that are common between two occupancies (intertenancy). The code specifies a Sound Transmission Class (STC) of not less than 55 for walls & floors. It also specifies an Impact Insulation Class (IIC)
for floors of not less than 55. STC rating relates to airborne noise transmission whereas IIC rating relates to impact noise transmission.
Although noise transmission requirements of the building code do not apply to stand alone homes, the living environment within these homes can be significantly improved by using concrete wall and floor systems which inherently have good noise
transmission reduction properties.
Typical STC Values for Concrete Walls
The following are typical STC values that have been obtained from testing conducted by the Prestressed Concrete Association in the USA for normal weight concrete.
|100 mm concrete wall
|150 mm concrete wall
|200 mm concrete wall
|150 mm precast or insitu concrete with carpet on underlay
|200 mm precast or insitu concrete with carpet on underlay
Even small openings can significantly reduce effectiveness. It is important to ensure there are no gaps that sound can pass through. Small gaps around services and unfilled joints must be adequately filled
Indirect Noise Transmission
Connection details and sound transmission properties of floors and ceilings are also important. The effectiveness of a wall in reducing sound transmission may be reduced if the sound can travel through
the ceiling into the next room.
The following figure from the New Zealand Concrete Masonry Manual illustrates the relationship between STC and the mass of the wall.
Sealing Masonry Walls
Because concrete masonry blocks are porous there will be some 'leaking' of sound. Sealing a block wall (usually with paint) has been shown to increase the STC rating by 3-5 STC points.
||Kg/m² of wall area
|Block Density 1750 kg/m³
|All cores filled
||2nd cores filled
||3rd cores filled
||4th cores filled
||No cells filled
|Block Density 2200 kg/m³