Page 96 - Build 161

Departments/LBP knowledge By Paul Hobbs, Registrar Building Practitioner Licensing
Reducing noise transmission
With higher-density housing becoming more widespread, designers and builders need to be up to speed with how wall assemblies can limit airborne and impact sound transmission between joined buildings.
AS NEW ZEALAND’S population grows, our district plans and long-term planning rules change to ensure we build enough homes for our residents. In many areas of the country, these changes have resulted in a move away from the traditional stand- alone dwelling to higher-density residential construction such as townhouses, terraced housing or apartments.
Noise reduction in a building
Sound insulation is a building element’s ability to reduce the sound that goes through it. It is generally given in a single unit number as a guide to its e ectiveness at limiting sound transmission, for example, sound transmission class (STC) 55 and impact insulation class (IIC) 55.
This single unit number is a summary of the element’s sound insulation performance over a range of frequencies. It’s important to note the single unit doesn’t give you a full picture at all frequencies. For example, an STC 55 timber wall won’t have exactly the
same performance at all frequencies as an STC 55 concrete wall.
Types of sound transmission
There are generally two types of sound transmission to consider for buildings:
● Airborne sound – noise originating in air,
for example, voices, music, motor tra c
and wind.
● Impact sound – noise originating directly
on a structure by blows or vibration, for example, footsteps above, furniture being moved, drilling and hammering the structure.
For wall assemblies, sound insulation should be thought of in two ways:
● External sound insulation – limiting noise
from outside the building. This is generally
provided by the building envelope.
● Internal sound insulation – limiting sound transmission within the building, for example, inter-tenancy sound insulation
or plumbing sound insulation.
The minimum requirements for preventing
sound transmission through building elements are given in New Zealand Building Code clause G6 Airborne and impact sound. Remember that if you undertake building work, it must comply with the Building Code regardless of whether it requires a building consent.
Wall assembly and sound insulation
As a general rule, reducing sound transmis- sion requires more mass or a separation of elements. Mass can be increased by using a thicker version of the same material or by using a denser material.
A range of factors need to be considered when selecting, installing or detailing noise control in wall, oor and ceiling assemblies (see Table 1). Always keep to the design specification for building elements that contribute to the sound insulation, particu- larly around inter-tenancy walls.
For more Information on Building Code clause G6 is available on MBIE’s Building Performance website at www.building.govt.nz/building-code- compliance/.
94 — August/September 2017 — Build 161