Part 4.2 Footings, slabs and associated elements

(1) Excavation for footings, including thickenings for slabs and pads must be clean cut with vertical sides, wherever possible.

(2) The base of the excavation must be—

1. for flat sites, generally level but may slope not more than 1:40 to allow excavations to drain; and
2. for sloping sites at an angle of not more than 1:10; and
3. for stepped footings in accordance with 4.2.7.

(3) Footing excavations must be free of loose earth, tree roots, mud or debris.

(4) Topsoil containing grass roots must be removed from the site of the foundation.

(5) On loose sand sites or sites subject to wind or water erosion, the depth below finished ground level to the bottom of footings must be not less than 300 mm.

(6) The height of a finished slab-on-ground must be in accordance with 3.3.3(b).

(1) A damp-proofing membrane must be installed under slab-on-ground construction for a Class 1 building and for a Class 10 building where the slab is continuous with the slab of a Class 1 building in accordance with (2), (3), (4) and (5).

(2) Materials: A damp-proofing membrane must be—

1. 0.2 mm nominal thickness polyethylene film; and
2. high impact resistant,

determined in accordance with criteria specified in clause 5.3.3.3 of AS 2870.

(3) A damp-proofing membrane must be branded continuously “AS 2870 Concrete underlay, 0.2 mm High impact resistance”.

(4) Installation: A damp-proofing membrane must be installed as follows—

1. Lap not less than 200 mm at all joints.
2. Tape or seal with a close-fitting sleeve around all service penetrations.
3. Fully seal where punctured (unless for service penetrations) with additional polyethylene film and tape.

(5) The damp-proofing membrane must be placed beneath the slab so that the bottom surface of the slab is entirely underlaid and must extend under internal and edge beams to finish at ground level in accordance with Figure 4.2.8.