Specification 28 Sound insulation for building elements

This Specification lists the weighted sound reduction index R_W for some common forms of construction.

The forms of construction listed in NT S28C3 are considered to have the R_W stated in that clause if installed as follows:

1. Masonry: units must be laid with all joints filled solid, including those between the masonry and any adjoining construction.
2. Concrete slabs: joints between concrete slabs and any adjoining construction must be filled solid.
3. Plasterboard—
   1. if one layer is required under this Specification, it must be screw-fixed to the studs with joints staggered on opposite faces; and
   2. if 2 layers are required, the first layer must be fixed according to (i) and the second layer must be fixed to the first layer with nails, screws or adhesive so that the joints do not coincide with those of the first layer; and
   3. joints between sheets or between sheets and any adjoining construction must be taped and filled solid; and
   4. fire-protective grade plasterboard must be the special grade manufactured for use in fire-resisting construction.
4. Steel studs and perimeter members—
   1. the section of steel must be not less than 0.6 mm thick; and
   2. studs must be not less than 63 mm in depth unless another depth is listed in NT S28C3; and
   3. studs must be fixed to steel top and bottom plates of sufficient depth to permit secure fixing of the plasterboard; and
   4. all steel members at the perimeter of the wall must be securely fixed to the adjoining structure and be bedded in resilient compound or the joints must be caulked so that there are no voids between the steel members and the wall.

(1) Construction in accordance with the following has an R^_W of not less than 45:

1. Walls — clay brickwork:
   1. 230 mm thick in one or more leaves and with a mass per unit area of not less than 290 kg/m².
   2. 110 mm thick rendered 13 mm thick on both sides with a mass per unit area of the unrendered wall being not less than 190 kg/m².
   3. 110 mm thick, of semi-dry-pressed bricks and rendering 13 mm on one side, the mass per unit area being not less than 215 kg/m².
   4. 110 mm thick, of extruded brick and rendered 13 mm on one side, the mass per unit area being not less than 180 kg/m².
2. Walls — concrete brickwork: 110 mm thick with a mass per unit area of not less than 195 kg/m².
3. Walls — concrete blockwork:
   1. 190 mm thick with a mass per unit area of not less than 215 kg/m².
   2. 140 mm thick, the wall thickness of the blocks being not less than 44 mm and with—
      1. 50 mm x 50 mm timber battens spaced at not more than 610 mm centres screw-fixed on one face of the blocks into resilient plugs with rubber inserts between the battens and the wall; and
      2. the face of the battens clad with 13 mm thick standard plasterboard; and
      3. a mass per unit area of the whole system of not less than 220 kg/m².
4. Walls — concrete:
   1. In-situ concrete — 125 mm thick and with a density of not less than 2200 kg/m³.
   2. In-situ concrete — 100 mm thick and with a density of not less than 2500 kg/m³.
   3. Precast concrete — 100 mm thick and without joints.
5. Walls — steel stud walling:
   1. With 2 layers of 16 mm thick fire-protective grade plasterboard fixed to each face.
   2. With—
      1. 1 layer of 13 mm thick fire-protective grade plasterboard fixed to one face, and before fixing, 50 mm thick mineral or glass wool blanket or batts stapled to the back of each sheet so that the sheet is completely covered; and
      2. 2 layers of 13 mm thick fire-protective grade plasterboard fixed to the other face.
   3. With—
      1. 1 layer of 16 mm thick fire-protective grade plasterboard fixed to one face; and
      2. 50 mm thick mineral or glass wool blanket or batts wedged firmly between the studs; and
      3. 2 layers of fire-protective grade plasterboard fixed to the other face, the inner layer being 16 mm thick and the outer layer being 13 mm.
   4. With 2 layers of 13 mm plasterboard on both sides of 75 mm studs.
6. Floors — concrete:
   1. In-situ concrete slab — 125 mm thick and with a density of not less than 2200 kg/m³.
   2. In-situ concrete slab — 100 mm thick and with a density of not less than 2500 kg/m³.
   3. Pre-cast concrete slab — 100 mm thick and without joints.
7. Floors — timber, comprising—
   1. timber joists not less than 175 mm x 50 mm; and
   2. 75 mm thick mineral or glass wool blanket or batts cut to fit tightly between joists and laid on 10 mm thick plasterboard fixed to underside of joists; and
   3. 25 mm thick mineral or glass wool blanket or batts laid over entire floor, including tops of joists before flooring is laid; and
   4. tongued and grooved boards not less than 19 mm thick, secured to 75 mm x 50 mm battens; and
   5. the assembled flooring laid over the joists, but not fixed to them, with the battens lying between the joists.

(2) Ducts or other construction separating soil and waste pipes from units, constructed in accordance with the following, have an R_W of not less than 30:

1. Masonry — not less than 90 mm thick.
2. Plasterboard — 2 layers of plasterboard:
   1. Each 10 mm thick, fixed to timber studs not less than 75 mm x 50 mm and spaced at not more than 400 mm centres.
   2. Each 13 mm thick, one on each side of steel studs not less than 50 mm deep and spaced at not more than 400 mm centres.