Class 3 - Accommodation or Residence in Public Building

Class 3 buildings are typically buildings where unrelated people may live, such as boarding houses, motels and residential parts of hotels. For a more complete definition refer to Clause A3.2 of the Building Code of Australia.

Sound transmission and Insulation

The objective of providing insulation to reduce sound transmission in a Class 3 Building is to prevent loss of amenity, due to undue sound being transmitted between units, or to a unit, from other parts of the building, such as plant rooms, lift shaft, common corridors, or from a different classification in the same building for example, car park, shops, commercial premises.

 Walls and floors separating a sole occupancy unit from other units must be insulated against the transmission of airborne sound, as well as impact sound. Accordingly the insulation value of these elements of construction must not be compromised by openings such as doors or services.

Compliance with the BCA

To achieve these objectives the walls and floors bounding an SOU must be constructed so as to satisfy the requirements of

  • Part F5 of the Building Code of Australia (BCA)
  • Specification F5.2 of the BCA
  • Manufacturer’s Specification to ensure that the product performs as tested.

Alternative Solution

If any of the above requirements cannot be met, either because of innovative development, or there is a particular construction issue, the building would not comply with the Deemed-to Satisfy Requirements of the Building Code of Australia and consequently a Construction Certificate or an Occupation Certificate will not be able to be issued.

To overcome this situation it may be possible to develop an Alternative Solution, in accordance with the requirements of Clause A0.8, A0.9, & A0.10 of the BCA, demonstrating that the method of construction will satisfy the Performance Requirements of Part F5; by:

  1. Providing evidence that the form of construction satisfies the BCA;
  2. Using a Verification Method as set out in the BCA such as FV 5.1, FV 5.2;
  3. Comparison with the Deemed-to-Satisfy provisions
  4. Expert judgement

Deemed to Satisfy Requirements

Construction considered to satisfy the requirements of the BCA can be achieved either by

  1. Adopting typical construction systems nominated in Specification F5.2 of the BCA, or
  2. By using results form laboratory measurements in accordance with AS/NZS 1276.1 or ISO 717.1 to achieve the following values:

Construction Details

Some typical construction details that must be followed to achieve required sound insulation levels include (but are not limited to):

(a)    Following the manufacturer’s specification;

(b)    Wall systems listed in Table 2 of Specification F.2 of the BCA must be discontinuous, which    
means a wall having a minimum cavity of 20 mm between two leaves, and

  • For masonry wall ties must be of the resilient type;
  • For other than masonry there must be no mechanical linkage between leaves except at the periphery

(c)    For masonry construction joints must be solid filled;

(d)    Joints between concrete slabs or panels and any abutting construction must be solid filled;

(e)    For sheet lining materials joints must be staggered

(f)    Timber or steel framing must be securely fixed and either bedded in a resilient compound, or the joints located between the framing and adjoining structure

(g)    Where a wall is required to have sound insulation, the wall must either extend to the underside of a floor or ceiling that has the required insulation.

(h)    Services must not be chased into concrete or masonry construction.

(i)     Shaft access doors or panels required to have sound insulations must not open into habitable rooms and must be securely fixed with a minimum 10 mm overlap composed of
        - Wood particle board etc at least 33 mm thick;
        - Fibre cement at least 9 mm thick;
        - Or material having a mass per unit area not less than 24.4kg/m2;

(j)    Water pipes only serving one unit located in a cavity wall must be fixed to the unit’s side of the wall, having a minimum clearance of 10 mm from the opposite wall leaf and each wall leaf must be of discontinuous construction;

(k)    Electrical outlets must be offset from each other in
        - Masonry wall by 100 mm and
        - Timber of steel framed wall by 300 mm

(l)    Insulation material used must be of the specified:
        - Material
        - Thickness
        - Density

Learn More

Class 3 BCA Energy requirements

Class 3 BCA Fire Requirements

Class 3 BCA Bushfire Requirements


Discontinuous construction:
Wall systems listed in Table 2 having a minimum 20 mm cavity between 2 separate leaves, with
(i)      For masonry, where wall ties are required to connect leaves, the ties are of the resilient type,
(ii)     For other than masonry, there is no mechanical linkage between leaves except at the periphery, are deemed to be discontinuous construction.

Habitable room means a room used for normal domestic activities, and—
(a) includes a bedroom, living room, lounge room, music room, television room, kitchen, dining room, sewing room, study, playroom, family room and sunroom; but
(b) excludes a bathroom, laundry, water closet, pantry, walk-in wardrobe, corridor, hallway, lobby, photographic darkroom, clothes-drying room, and other spaces of a specialised nature occupied neither frequently nor for extended periods

Verification Method
means a test, inspection, calculation or other method that determines whether a Building Solution complies with the relevant Performance Requirements.