Part F5 Sound transmission and insulation (DtS)

Throughout the Part F5 Deemed-to-Satisfy Provisions, some forms of construction are required to have an R_w or R_w + C_tr. R_w and C_tr must be:

• determined under AS/NZSISO 717.1 using laboratory measurements; or

• in compliance with Specification F5.2.

R_w is a measure of airborne sound insulation. C_tr is a spectrum adjustment factor which adjusts for low frequency sound levels. C_tr has been chosen in recognition of the problems caused by the high bass frequency outputs of modern home theatre systems and music reproduction equipment used by occupants of Class 2 and 3 buildings.

The R_w and C_tr must be determined in accordance with either AS/NZS ISO 717.1. These documents outline how to use test results from testing a building element to determine the R_w and C_tr of the building element. The test results must be obtained by testing the building element in accordance with ISO 140-3. ISO 140-3 is the method for testing the airborne sound insulation of building elements in the laboratory.

This part previously referenced Sound Transmission Class (STC) ratings as a measure of sound insulation. The STC rating has been replaced by R_w and R_w + C_tr. A note contained in Schedule 4 under AS/NZS ISO 717.1 states that materials tested in accordance with the previous Standard AS 1276 – 1979 must be considered equivalent to R_w values. These tests are only valid if they were issued prior to AS/NZS 1276.1 – 1999 being referenced in the BCA.

In F5.4(a) floors separating certain areas are required to have an L_n,w. F5.3(a) outlines that the L_n,w must be:

• determined under AS ISO 717.2 using laboratory measurements; or

• in compliance with Specification F5.2.

L_n,w is a measure of impact sound insulation. The types of impact generated noise passing through floors that the requirements are aimed at minimising are noise associated with footsteps and moving of furniture.

F5.3(b)(i) requires walls of Class 2 and 3 buildings required to have an impact sound insulation rating to be of discontinuous construction. This term is defined in F5.3(c) and applies to all of Part F5 including Specifications F5.2 and F5.5.

F5.3(b)(ii) requires walls of a Class 9c building required to have an impact sound insulation rating to:

• for other than masonry, consist of at least two separate leaves that do not have any rigid mechanical connection except at the periphery. (The reason for not allowing rigid connection is to reduce the transmission of impact sound to the sleeping area); or

• be identical with a prototype having at least the same resistance to impact sound as a wall complying with Table 2 of Specification F5.2.

F5.3(c) sets out a definition of discontinuous construction. The definition applies to the whole of Part F5 (including Specifications F5.2 and F5.5) and is a wall having a cavity of at least 20 mm between 2 leaves, and:

• for masonry, only be connected with resilient wall ties (these are a particular type of wall tie and are sometimes referred to as acoustic wall ties); and

• for other than masonry, other than at the periphery, have no mechanical linkage between the leaves. This means that a staggered stud wall is not deemed to be discontinuous construction.

F5.4 contains requirements for Class 2, 3 and 9c buildings.

For Class 2 and 3 buildings, a floor requires both airborne (R_w + C_tr) and impact sound insulation (L_n,w) if it separates:

• sole-occupancy units;

• a sole-occupancy unit from a plant room, lift shaft, stairway, public corridor, public lobby or the like; or

• parts of a different classification.

For Class 9c buildings, a floor requires airborne sound insulation if it separates sole-occupancy units.

The requirements differ between Class 2 and 3 buildings, and Class 9c buildings. This is due to sole-occupancy units in Class 2 and 3 buildings being ‘noisier’ than sole-occupancy units in Class 9c buildings. The reasons include the presence of televisions, stereos and DVDs and activities that may be conducted in Class 2 and 3 buildings. Therefore, C_tr and impact sound insulation only apply to Class 2 and 3 buildings. Also, the level of airborne sound insulation required in Class 9c buildings is less.

F5.5(a) and (b) apply to Class 2 and 3 buildings. F5.5(a) covers walls separating sole-occupancy units, and walls separating sole-occupancy units and certain spaces. F5.5(b) applies to a door assembly in a wall that separates a sole-occupancy unit from a common area. F5.5(c) and (d) apply to Class 9c buildings. F5.5(c) applies to walls which separate sole-occupancy units and sole-occupancy from certain spaces. F5.5(d) applies to a wall that separates a sole-occupancy unit from a kitchen or laundry. F5.5(e) and (f) contains additional requirements for sound insulated walls.

As with the requirements for floors, the requirements for walls differ between Class 2 and 3 buildings, and Class 9c buildings. This is due to sole-occupancy units in Class 2 and 3 buildings being ‘noisier’ than sole-occupancy units in Class 9c buildings. The reasons include the presence of televisions, stereos and DVDs and activities that may be conducted in Class 2 and 3 buildings. Therefore, Ctr only applies to Class 2 and 3 buildings. Also, the level of airborne sound insulation required in Class 9c buildings is less.

F5.5(a) outlines airborne and impact sound insulation requirements for walls. The airborne sound requirements apply to walls separating sole-occupancy units and a sole-occupancy unit from a plant room, lift shaft, stairway, public corridor, public lobby or the like, or parts of a different classification. For walls separating sole-occupancy units, the wall must have a R_w + C_tr not less than 50. For walls separating a sole-occupancy unit from a plant room, lift shaft, stairway, public corridor, public lobby or the like, or parts of a different classification, the wall must have a R_w not less than 50. For walls separating habitable areas (excluding a kitchen) in one sole-occupancy unit from a bathroom, laundry, kitchen or sanitary compartment in an adjoining unit, the wall must be discontinuous construction. For the purpose of the BCA, discontinuous construction is a wall having a minimum 20 mm cavity between 2 separate leaves, with:

• for masonry, where wall ties are required to connect leaves, the ties are of the resilient type; and

• for other than masonry, there is no mechanical linkage between leaves, except at the periphery.

Mechanical linkage at the periphery is referring to the connection of the wall to the floor/roof and adjoining walls such as an external wall etc. A staggered stud wall with common top/bottom plates is not considered to be discontinuous construction.

F5.5(b) provides a concession for a door assembly located in a wall that separates a sole-occupancy unit from public corridor or the like. The door requires an R_w of not less than 30 whereas the wall requires R_w of not less than 45. This concession does not apply to a door assembly in a wall separating sole-occupancy units. In this case the door assembly would need to meet the same requirements for the wall, i.e. R_w + C_tr 50.

F5.5(c) applies to Class 9c buildings and covers sound transmission through sole-occupancy units from certain adjoining rooms and spaces. The list of adjoining rooms and spaces does not include the words ‘or the like’ because it is intended to be specific to only those areas.

The list of other spaces in F5.5(c) does not include stairways, public corridors, hallways, etc. The reason is that aged care buildings are to be provided with a level of sound insulation around the resident bedroom/sleeping areas to ensure a level of privacy, but still allow the residents to be reassured they are not alone. If the R_w of the wall is too high it may create a feeling of isolation for the residents and this can be detrimental to their well being. Being able to hear sounds that are outside their bedroom provides reassurance that assistance is available. The walls of sole-occupancy units prescribed in F5.5(c) must be at least R_w 45.

F5.5(d) applies to Class 9c buildings and deals with reducing the level of impact sound through the walls of the sole-occupancy units from adjoining kitchens and laundries. To comply with F5.5(d), it is necessary for the wall to have an R_w not less than 45 (as required by F5.5(c)) and:

• for other than masonry, consist of at least two separate leaves that do not have any rigid mechanical connection except at the periphery. (The reason for not allowing rigid connection is to reduce the transmission of impact sound to the sleeping area); or

• be identical with a prototype having at least the same resistance to impact sound as a wall complying with Table 2 of Specification F5.2.

F5.5(e) and (f) requires sound insulated walls to extend to either the roof/floor above or a ceiling that provides the required level of sound insulation. This is to ensure that there is no space above the wall which provide a flanking path for sound to travel through.

F5.6 details separation requirements for services. The requirements only apply to services which pass through more than one sole-occupancy unit or are located in a wall or floor cavity which separates sole-occupancy units. F5.6 does not apply if the pipe is only located in a single unit, or any part of a Class 2, 3 or 9c building which is not part of a sole-occupancy unit.

The R_w + C_tr values do not take account of the inherent acoustic properties of a pipe material.

F5.7 requires flexible couplings at connection points to or from a pump to minimise vibration and any consequent sound transmission along the piping.